TABLE OF METRIC AND ENGLISH MEASURES. 
The measures of length, volume and weight most frequently employed in micro- 
scopical and histological work are the following: 
1000 Microns (/u) = 1 Millimeter. 
10 Millimeters (m.m.) = 1 Centimeter. 
100 Centimeters (cm. or ctm.) = 1 Meter (unit of length). 
1 M = 0.000039 inch, in. approximately. 
1 cm. = 0.3937 in. 
1 Meter =-= 39.3704 in. 
LENGTH. 
VOLUME. 
1000 Cubic centimeters (cc. or cctm.) or milliliters = 1 Liter (1000 grams of 
water) (unit of volume). 
1 Fluid ounce (8 Fluidrachms) = 29.578 cc. 
WEIGHT. 
1000 Grams = 1 Kilogram (the weight of 1000 cc. or 1 liter of water). 
1 Gram (unit of weight) = 15.432 Grains. 
1 Kilogram = 2.204 Avoirdupois pounds. 
1 Ounce Avoirdupois (437)4 grains) = 28.349 Grams. 
1 Ounce Troy or Apothecaries (480 grains) = 31.103 Grams. 
TEMPERATURE. 
To change Centigrade to Farenheit: (C. X f) + 32 = F. For example, to find 
the equivalent of io° Centigrade C. = io° (io° X f) 4- 32 = 50° F. 
To change Farenheit to Centigrade : (F. — 320) X f = C. For example, to re- 
duce 50° Farenheit to Centigrade, F. = 50°, and (50° — 320) X | = io° C. ; or — 40 
Farenheit to Centigrade : F. = — 40° (— 40° — 320) = — 720, whence — 720 X f 
= - 40° C. 
For the price 
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R. Spencer & THE 
MICROSCOPE AND HISTOLOGY 
, FOR THE USE OF LABORATORY STUDENTS IN THE ANATOMICAL 
DEPARTMENT OF CORNELL UNIVERSITY, ' 
BY 
SIMON HENRY GAGE, 
Associate Professor of Physiology 
THIRD EDITION, ENTIRETY RE-WRITTEN. 
Part I. 
THE MICROSCOPE 
AND 
MICROSCOPICAL METHODS. 
ILLUSTRATED. 
ITHACA, NEW YORK, 
1891. Copyright, 1891, 
By Simon Heney Gage. 
All Rights Reserved. 
Printed and for sale by 
Andrus & Church, 
Ithaca, N. Y. PREFACE TO PART I. 
This, the third edition of “Notes on Microscopical Methods for the Use of Stu- 
dents in the Anatomical Department of Cornell University,” has been entirely re- 
written, enlarged, and more fully illustrated ; and while elementary matters have 
received fuller treatment than in previous editions, in this, an especial effort has 
been made to give a more adequa'e account of Homogeneous Immersion Object- 
ives, the Sub-Stage Illuminator. Camera Lucidas, the Micro-Spectroscope and 
Micro-Polariscope, that is to apparatus which is coming to be used more and more 
in the higher fields of investigation in pure science and in practical medicine. 
It is thoroughly believed by the writer that simply reading a work on the micro- 
scope, and looking a few times into an instrument completely adjusted by another, 
is of very little value in giving real knowledge. In order that the knowledge shall 
be made alive, it must be made a part of the student’s experience by actual experi- 
ments carried out by the student himself. Consequently exercises illustrating the 
principles of the microscope and the methods of its employment have been made 
an integral part of the work. 
In considering the real greatness of the microscope, and the truly splendid serv- 
ice it has rendered, the fact has not been lost sight of that the microscope is, after 
all, only an aid to the eye of the observer, only a means of getting a larger image 
on the retina than would be possible without it; but the appreciation of this retinal 
image, whether it is made with or without the aid of a microscope, must always 
depend upon the character and training of the seeing and appreciating brain behind 
the eye. The microscope simply aids the eye in furnishing raw material, so to 
speak, for the brain to work upon. 
The necessity for doing a vast deal of drudgery or “dead work,” as it has been 
happily styled by Prof. Leslie, before one has the training necessary for the appre- 
ciation and the production of original results, has been well stated by Beale : 
“The number of original observers emanating from our schools will vary as prac- 
tical work is favored or discouraged. It is certain that they who are most fully 
conversant with elementary details and most clever at demonstration, will be most 
successful in the consideration of the higher and more abstruse problems, and will 
feel a real love for their work which no mere superficial inquirer will experience. 
It is only by being thoroughly grounded in first principles, and well practised in 
mechanical operations, that any one can hope to achieve real success in the higher 
branches of scientific enquiry, or to detect the fallacy of certain so-called experi- 
ments.” 
In preparing this manual it has been taken for granted that the student is al- 
ready familiar with elementary physics, especially the subject of optics. 
The experiments in micro-chemistry (Ch. V.) are given for the sake of practice 
for the junior chemical students who take the course in order to gain a knowledge 
of the microscope as an aid to chemistry. 
In Part II will be given the application of the microscope to study and investi- 
gation in Vertebrate Histology. 
SIMON HENRY GAGE, 
Corneee University, 
Ithaca, New York, U. S. A. 
October i, 1891. THE MICROSCOPE AND HISTOLOGY. 
CONTENTS OF PART I. 
CHAPTER I. 
PAGE 
|| 1-74. The Microscope and its Parts—Care and Use, 1-28 
CHAPTER II. 
|| 75-96. Interpretation of Appearances, 29-35 
CHAPTER III. 
|| 97-127. Magnification, Micrometry and Drawing, 36-53 
CHAPTER IV. 
|| 128-157. The Micro-Spectroscope and Micro-Polariscope, 54-65 
CHAPTER V. 
1% 158-200. Slides and Cover-Glasses, Mounting, Labeling, Cataloging and 
Storing Microscopical Preparations ; Experiments in Micro- 
Chemistry, 66-85 
Bibliography, 86-90 
Index, 91-96 LIST OF ILLUSTRATIONS. 
All of the Figures, except when otherwise indicated, are original, and were drawn 
by Mrs. Gage. 
PLATES. 
Fig. 
PLATE I. 
1. Double convex lens showing the principal plane, the principal focus, and the 
focal distance. 
2. Converging lens showing formation of a virtual image. 
3. Converging lens showing formation of a real image. 
4. Simple microscope with retinal image, and its projection as a virtual image. 
5. Compound microscope, tracing the rays from the object to the final, virtual 
image. 
6. Huygenian ocular or eye-piece, showing action of field-lens (Ross). 
7. Huygenian ocular showing the eye-point. 
PLATE II. 
9. Tripod magnifier. 
10. Stand of a compound microscope with names of parts. 
11. Section of stage of compound microscope showing proper position of dia- 
phragms. 
12. Section of a low, dry objective and reflected light. 
13. Section of an adjustable, immersion objective, transmitted axial and oblique 
light. • 
14. Diagram showing how to put on a cover-glass. 
15. Slides showing how to enclose the lines of a micrometer or of some part of a 
preparation by a small ring. 
16. Double eye-shade. 
PLATE III. 
20-22. Sectional views of the Abbe illuminator showing various methods of illu- 
mination,—with parallel rays of central light, with oblique light, with con- 
verging rays, and for dark-ground illumination. 
23. Letters mounted in stairs to show order of coming into focus. 
24. Glass rod in air and in glycerin. 
25. Glass rod coated with collodion to show double contour. 
26. Blood corpuscles on edge, to show surface and optical sections. 
27. Wollaston’s camera lucida in section, showing the overlapping fields. 
28. Position of the microscope for determining magnification with Wollaston’s 
camera lucida ; also the necessity of a standard distance at which to measure 
the image. 
29. Figures of the image of the stage and ocular micrometers, showing correct mu- 
tual arrangement of lines in determining the ocular micrometer valuation. PLATE IV. 
30. Sectional view of the Abbe camera lucida with a 450 mirror and a horizontal 
drawing surface. 
31. Geometrical figure of the preceding showing the angles made by the axial ray 
with the drawing surface and with the mirror. 
32. Sectional view of the Abbe camera lucida with a 350 mirror, showing the nec- 
essary elevation of the drawing surface to avoid distortion. 
33. Geometrical figure of the preceding showing angles of axial ray and of draw- 
ing board, and that the drawing board must be raised twice as many degrees 
as the mirror is depressed below 450. 
34. Diagram showing arrangement of drawing board with mirror at 350 and with 
the microscope inclined 30° (Mrs. Gage). 
35. Upper view of the prism of the camera lucida. 
36. Eye-point of an ocular. 
37. Quadrant with graduations to be added to the mirror of the Abbe camera lucida 
to determine the inclination of the mirror. 
PLATE V. 
41. Effect of the cover-glass on the rays from the object to the objective (Ross). 
42. Direction of the rays from an object through a cover-glass in a dry objective. 
43. Direction of the rays with a water immersion objective. 
44. Direction of the rays with a homogeneous immersion objective. (Fig. 42-44 
are modified from Ellenberger). 
45. Absorption spectrum of arterial and venous blood; some of the principal 
Fraunhofer lines and an Angstrom scale are also shown. (From Gamgee 
and MacMunn). 
46. Centering card. 
47. Small spirit lamp used as a reagent bottle for Canada balsam, glycerin jelly, 
shellac cement, etc. 
48. Pipette or dropper for delivering small quantities of any liquid. 
49. Slide and cover-glass showing the method of irrigation. 
50. Showing the method of anchoring the cover-glass previous to sealing glycerin- 
mounted objects. # 
51-56. Various apparatus for the study of fibrin and the counting of blood corpus- 
cles. (These figures appertain to Part II). 
Fig. 
FIGURES IN THE TEXT. 
Page. 
8. Triplet for the pocket (Bausch & Lomb Optical Company), 2 
8a. Simple microscope with stand (R. & J. Beck), 2 
8b. Figure showing parts included in tube-length by various opticians, ... 6 
17. Double nose-piece or revolver (Bausch & Domb Optical Co.), 11 
18. Ward’s eye-shade (Bausch & Lomb Optical Co.), 27 
19. Oil-globule and air-bubble, with oblique light, 32 
38. Cover-glass measurer (Edward Bausch), 69 
38a. Turn-table for sealing cover-glass, etc., (James W. Queen & Co.),. . . . 71 
39. Cabinet for specimens, 80 
40. Cabinet drawer, face and sectional view, . 81 
57. Arranging and labeling serial sections, 78 THE MICROSCOPE AND HISTOLOGY. 
CHAPTER I. 
THE MICROSCOPE AND ITS PARTS—CARE AND USE. 
APPARATUS AND MATERIAL FOR THIS CHAPTER. 
A simple microscope ($ 2, 4); A compound microscope with nose-piece (Fig. 17), 
eye-sliade (Fig. 16, 18', achromatic ($ 12), apochromatic ($ 14), dry 9), immersion 
($10), unadjustable and adjustable objectives (§ 15, 16), Huygenian or negative 
(§ 20, 22), positive (§ 21) and compensation oculars ($ 23), Abbe illuminator (54), 
homogeneous immersion liquid (§ 10, 65-69), benzine and distilled water (§ 64, 
69). Mounted letters or figures ($ 34) ; Ground-glass and Japanese filter or bib- 
ulous paper ($ 34, 72); Mounted preparation of fly’s wing ($ 50) ; Mounted prepa- 
ration of Pleurasigma (§ 52, 53, 58) ; Stage or ocular micrometer with lines 
filled with graphite (§ 52, 53, 59) ; Glass slides and cover glasses (§ 52) ; 10 per ct. 
solution of salicylic acid in 95 per ct. alcohol (§ 60); Preparation of stained mi- 
crobes (§ 67) ; Vial of equal parts olive or cotton seed oil and benzine (§ 71). 
Of the above, the laboratory furnishes all except the tripod magnifier, the glass 
slides and cover-glasses ; these must be obtained by the student. 
A MICROSCOPE. 
$ i. A Microscope is an optical apparatus with which one may obtain a clear 
image of a near object, the image being always larger than the object; that is, it 
enables the eye to see an object under a greatly increased visual angle, as if the 
object were brought very close to the eye without affecting the distinctness of 
vision. Whenever the microscope is used for observation, the eye of the observer 
forms an integral part of the optical combination (PI. I, Fig. 4 and 5). 
| 2. A Simple Microscope.—With this an enlarged, erect image of an object may 
be seen. It always consists of one or more converging lenses or lens-systems (PI. 
I, Fig. 1, 2 and 4), and the object must be placed within the principal focus (£ 4). 
The simple microscope may be held in the hand or it may be mounted in some way 
to facilitate its use (Fig. 8a). 
| 3. A Compound Microscope.—This enables one to see an enlarged, inverted 
image. It always .consists of two optical parts,—an objective, to produce an en- 
larged, inverted, real image of the object, and an ocular acting in general like a 
simple microscope to magnify this real image (PI. I, Fig. 5). There is also usually 
present a mirror, or both a mirror and some form of condenser or illuminator for 
lighting the object. The stand of the microscope consists of certain mechanical 
arrangements for holding, the optical parts and for the more satisfactory use of 
them (PI. II, Fig. 10). EXPLANATION OF PLATE I. 
In all of the figures, Virtual Images and rays traced backward or produced rays, 
are indicated by dotted or broken lines, real rays or paths of rays by full or un- 
broken lines. 
Fig. i. Sectional view of a double convex lens showing : (A B) the principal 
plane at which the refractions of the curved surfaces are most conveniently shown ; 
(c) Optical Center of the lens. Rays traversing this center undergo no deviation. 
Axis. Principal optic axis of the lens, i. e., line connecting the centers of cur- 
vature of the two surfaces of the lens. The axis traverses the optical center and 
the principal focal point or focus (F). F. Principal focal point or focus, i. e., the 
point where central parallel rays are brought to a focus. 
F I). Principal focal distance, or focal length, i. e., the distance between the cen- 
ter of the lens (c) and the principal focus (F). 
Fig. 2. Convex lens showing the position of the object (A B) within the princi- 
pal focus and the course of rays in the formation of a virtual image. 
A B. The object placed between the lens and its focus ; A' W virtual image 
formed by tracing the rays backward. It appears on the same side of the lens as 
the object, and is erect ($ 4). 
Axis. The optic axis of the lens. The principal focus is represented by a dot 
on the axis between the object and virtual image. 
1, 2, 3. Rays from the point B of the object. They are diverging after travers- 
ing the lens, but not so divergent as if no lens were present, as is shown by the 
dotted lines. Ray 1 traverses the center of the lens, and is therefore not deviated. 
Fig. 3. Convex lens showing the position of the object (A-B) outside the princi- 
pal focus (F), and the course of the rays in the formation of real images. To avoid 
confusion the rays are drawn from only one point, as in Fig. 2. 
A B. Object outside the principal focus. B/ A'. Real, enlarged image on the op- 
posite side of the lens. 
Axis. Principal optic axis. 1, 2, 3. Rays after traversing the lens. They are 
converging, and consequently form a real image. The dotted lines and the line 2 
give the direction of the rays unaffected by the lens. F. The principal focus. 
Fig. 4. Diagram of the simple microscope showing the course of the rays and all 
the images, and that the eye forms an integral part of it. 
A B. The object within the principal focus. A' B/. The virtual image on the same 
side of the lens as the object. It is indicated with dotted lines, as it has no actual 
existence. 
A2 B '. Retinal image of the object (A B). The virtual image is simply a projec- 
tion of the retinal image in the field of vision. 
Axis. The principal optic axis of the microscope and of the eye. Cr. Cornea 
of the eye. D Crystalline lens of the eye. R. Ideal refracting surface at which 
all the refractions of the eye may be assumed to take place. 
Fig. 5. Diagram of a compound microscope, showing the course of the rays from 
the object (A’B1) through the objective to the real image (BA), thence through 
the ocular and into the eye to the retinal image (A2 B2), and the projection of the 
retinal image into the field of vision as the virtual image (B/ A/). 
A3 B\ The object. A2 B2. The retinal image of the inverted real image, BA, formed by the objective. B' A.'. The inverted virtual image, a projection of the 
retinal image. 
Axis. The optic axis of the microscope and the eye. 
Cr. Cornea of the eye. h. Crystalline lens of the eye. R. Single, ideal, refract- 
ing surface at which all the refractions of the eye may be supposed to take place. 
F. The principal focus of the positive ocular. F'. The principal focus of the ob- 
jective. 
Mirror. The mirror reflecting parallel rays to the object. The light is central 
($ 42). 
Pos. Ocular. An ocular in which the real image is formed outside the ocular. 
Compare the positive ocular with the simple microscope (Fig. 4). 
Fig. 6. Hg. Ocular. Huygenian ocular showing the general character of a neg- 
ative ocular, and the action of the field and eye-lenses. (From Carpenter, after 
A. Ross). 
B B. Blue image, convex to the eye-lens, that would be formed if no field-lens 
were present. 
R R. Red image, convex to the eye-lens, that would be formed but for the pres- 
ence of the field-lens. B B and R R show also that the objective is over-corrected 
for the blue rays, as the blue image is formed farther from the objective than the 
red image. As blue rays are more refrangible than red, the image would naturally 
be nearer the objective than the red image. 
B/ B' R' Rr. Blue and red real images as actually formed under the influence of 
the field-lens. Both are concave to the eye-lens, and “ as the focus of the eye- 
lens is shorter for blue rays than for red rays by just the amount of the difference 
in the place of these images, their rays, after refraction by it, enter the eye in a 
parallel direction, and produce a picture free from false color.” The field-lens 
also aids in rendering the field flat. 
E F. Eye-lens. F F. Field-lens. 
Fig. 7. Sectional view of a Huygenian ocular (Hg. ocular), to show the forma- 
tion of the Eye-Point. 
Axis. Optic axis of the ocular. D. Diaphragm of the ocular. E F. Eye-lens. 
F F. Field-lens. 
E P. Eye-point. As seen in section, it appears something like an hour-glass. 
When seen as in looking at the ocular, i. e., in transection, it appears as a circle of 
light It is at the point where most rays cross. EXPLANATION OF PLATE II. 
Fig. 9. Tripod Magnifier. The frame holding the lenses may be raised or low- 
ered (focused) by screwing it up or down in the outside ring. 
Fig. 10. Stand. That is the mechaical parts of a simple form of compound mi- 
croscope, with the names of the parts written upon them. 
Arm. The part connecting the body or tube to the pillar. 
Base. The part of the stand on which it rests. It should be heavy and so formed 
that it will give steadiness, and not be in the way of the mirror. 
Body. The tube and draw-tube together. Also frequently called the tube. 
Coarse Adjustment. The rack and pinion for moving the tube or body rapidly 
up or down. 
Fine Adjustment. The micrometer screw arrangement for moving the body or 
tube of the microscope slowly up or down. 
Compressor. One of the pair of light springs to hold the preparation in position 
on the stage. 
Flexible Pillar. The pillar of the microscope, with a ioint to incline the micro- 
scope. 
Mirror. The movable mirror with plane and concave face for lighting the object. 
Mirror Bar. The bar supporting the mirror. 
Society Screw. The screws at the lower end of the draw-tube and the main tube 
or body tube for receiving the objective. 
Stage. The horizontal plate for supporting the object. 
Substage. The cylinder below the stage for diaphragms, the illuminator and 
other substage accessories. 
Fig. 11. Sectional view of the stage to show the relative position of the prepara- 
tion and the diaphragms necessary to insure the most satisfactory lighting when a 
mirror is used. 
F'ig. 12. Section of a dry objective showing working distance and lighting by 
reflected light. 
Axis. The optic axis of the objective. 
B C. Back Combination, composed of a plano-concave of flint glass (F), and a 
double convex of crown glass (c). 
F C. Front Combination. 
C O si. The cover-glass, object and slide. 
Mirror. The mirror is represented as above the stage, and as reflecting paral- 
lel rays from its plane face upon the object. 
Stage. Section of the stage of the microscope. 
W. The Working Distance, that is the distance from the front of the objective 
to the object when the objective is in focus (£ 38). 
Fig. 13. Sectional view of an Immersion Adjustable Objective, and the object 
lighted with axial or central and with oblique light. 
Axis. The optic axis of the objective. 
B C, M C, F C. The back, middle and front combinations of the objective. In 
this case the front is not a combination, but a single plano-convex lens. 
A B. Parallel rays reflected by the mirror axially or centrally upon the object. 
C. Ray reflected to the object obliquely. 
I. Immersion fluid between the front of the objective and the cover-glass or ob- 
ject O). 
Mirror. The mirror of the microscope. 
O. Object. It is represented without a cover-glass. Ordinarily objects are cov- 
ered whether examined with immersion or with dry objectives. 
Stage. Section of the stage of the microscope. 
Fig. 14. Diagram showing how to place a cover-glass upon an object with fine 
forceps. 
F'ig. 15. Diagram showing how to enclose the lines of a micrometer, or of some 
part of a preparation by a small ring to facilitate finding it under the microscope 
(3 32). 
Fig. 16. Double eye-shade (g 73). This is made by cutting a hole slightly larger 
than the tube near one edge. A rubber band is then used to loop around the tube 
and holding the screen from falling over in front. It is desirable to have the 
screen covered with velveteen. 2 
MICROSCOPE AND ACCESSORIES. 
SIMPLE MICROSCOPE : EXPERIMENTS. 
§ 4- Employ a tripod or other simple microscope, and for object a 
printed page. Hold the eye about two centimeters from the upper sur- 
face of the magnifier, then alternately raise and lower the magnifier until 
a clear image may be seen. (This mutual arrangement of microscope 
and object so that a clear image may be seen, is called focusing, see § 
37). When a clear image is seen, note that the letters appear as with 
the unaided eye except that they are larger, and the letters appear erect 
or right side up, instead of being inverted, as with the compound mi- 
croscope (§ 3, 34). 
Hold the simple microscope directly toward the sun and move it away 
from and toward a piece of printed paper until the smallest bright point 
on the paper is obtained. This is the burning point or focus, and as 
the rays of the sun are nearly parallel, the burning 
point represents approximately the principal focus 
(Fig. i). Without changing the position of the paper 
or the magnifier, look into the magnifier and note that 
the letters are very indistinct or invisible. Move the 
magnifier a centimeter or two farther from the paper 
and no image can be seen. Now move the magnifier 
closer to the paper, that is, so that it is less than the fo- 
cal distance from the paper, and the letters will appear 
distinct. This shows that in order to see a distinct image 
with a simple microscope, the object must always be 
nearer to it than its principal focal point. Or, in other words, the object 
must be within the principal focus. Compare § 34. 
After getting as clear an image as possible with a simple microscope, 
do not change the position of the micro- 
scope but move the eye nearer and farther 
from it, and note that when the eye is in 
one position, the largest field may be seen 
(§ 33)- This position corresponds to the 
eye-point (§ 36) of an ocular, and is the 
point at which the largest number of rays 
from the microscope enter the eye. Note 
that the image appears on the same side of 
the magnifier as the object (§ 34). 
Simple microscopes are very convenient 
when only a small magnification (Ch. Ill) 
is desired, as for dissecting. Achromatic 
triplets are excellent and convenient for the 
pocket (Fig. 8). For use in conjunction 
with a compound microscope, the tripod 
Fig. 8. — Achromatic 
Triplet for the Pocket. 
Fig.8“.—Simple Microscope with Special 
Mechanical Mounting to Hold and 
Focus the Magnifier and to Support 
and Light the Object. 3 
MICROSCOPE AND ACCESSORIES. 
magnifier (Plate II, Fig. 9) is one of the best forms. For many pur- 
poses a special mechanical mounting like that of Fig. 8a is to be pre- 
ferred. 
COMPOUND MICROSCOPE. 
MECHANICAL PARTS. 
\ 5. The Mechanical Parts of a laboratory, compound microscope are shown in 
PI. II, Fig. 10, and are described in the explanation of that figure. The student 
should study the figure with a microscope before him and become thoroughly fa- 
miliar with the names of all the parts. 
OPTICAL PARTS. 
\ 6. Microscopic Objectives.—These consist of a converging lens or of one or 
more converging lens-systems, which give an enlarged, inverted, real image of the 
object (PI. I, Fig. 3 and 5). And as for the formation of real images generally, the 
object must be placed outside the principal focus, instead of within it, as for the 
simple microscope. (See \\ 4, 34). 
Modern microscopic objectives usually consist of two or more systems or com- 
binations of lenses, the one next the object being called the front combination or 
lens, the one farthest from the object and nearest the ocular, the back combina- 
tion or system. There may be also one or more intermediate systems. Each 
combination is, in general, composed of a convex and a concave lens. The com- 
bined action of the systems serves to produce an image free from color and from 
spherical distortion. In the ordinary achromatic objectives the convex lenses are 
of crown and the concave lenses of flint glass (Pi. II, Fig. 12, 13). 
NOMENCLATURE OR TERMINOLOGY OF OBJECTIVES. 
\ 7. Equivalent Focus.—In America, England, and sometimes also on the 
Continent, objectives are designated by their equivalent focal length. This 
length is given either in inches (usually contracted to in.) or in millimeters (mm.). 
Thus : An objective designated in. or 2 mm., indicates that the objective pro- 
duces a real image of the same size as is produced by a simple converging lens 
whose principal focal distance is j inch or 2 millimeters (PI. I, Fig. 1). A11 
objective marked 3 in. or 75 mm., produces approximately the same sized real im- 
age as a simple converging lens of 3 inches or 75 millimeters focal length. And 
in accordance with the law that the relative size of object and image vary directly 
as their distance from the center of the lens (PI. I, Fig. 2, 3), it follows that the 
less the focal distance of the simple lens or of the equivalent focal distance of the 
objective, the greater is the size of the real image. 
\ 8. Numbering or Lettering Objectives.—Instead of designating objectives by 
their equivalent focus, many Continental opticians use letters or figures for this 
purpose. With this method the smaller the number, or the earlier in the alpha- 
bet the letter, the lower is the power of the objective. (See further in Ch. Ill, 
for the power or magnification of Objectives.) This method is entirely arbitrary 
and does not, like the one above, give direct information concerning the ob- 
jective. 4 
MICROSCOPE AND ACCESSORIES. 
| 9. Dry Objectives.—These are objectives in which the space between the 
front of the objective and the object or cover-glass is filled with air (Pi. II, Fig. 
12). Most objectives of low and medium power (i. e.f j4th in. or 3 mm. and 
lower powers) are dry. 
\ 10. Immersion Objectives.—An immersion objective is one with which there 
is some liquid placed between the front of the objective and the object or cover- 
glass. The most common immersion objectives are those (A) in which water is 
used as the immersion fluid, and (B) where some liquid is used having the same 
refractive and dispersive power as the front lens of the objective. Such a liquid 
is called homogeneous, as it is optically homogeneous w’itli the front glass of the 
objective. It may consist of thickened cedar-wood oil or of glycerin containing 
some salt, as stannous chloride, in solution. When oil is used as the immersion 
fluid the objectives are frequently called oil-immersion objectives. The disturb- 
ing effect of the cover-glass ($$ 16, 63) is almost wholly eliminated by the use of 
homogeneous immersion objectives. 
The course of the rays of light from the object to the objective with dr}' and 
different forms of immersion objectives is shown in PI. V, Fig. 42, 43, 44. 
| 11. Non-Achromatic Objectives.—These are objectives in which the chro- 
matic aberration is not corrected, and the image produced is bordered by colored 
fringes. They show also spherical aberration and are used only on very cheap 
microscopes. 
§ 12. Achromatic Objectives.—In these the chromatic and the spherical aber- 
ration are both largely eliminated by combining concave and convex lenses of 
different kinds of glass “so disposed that their opposite aberrations shall correct 
each other.” All the better forms of objectives are achromatic and also aplanatic 
(§ 13). 
\ 13. Aplanatic Objectives, etc.—These are objectives or other pieces of optical 
apparatus (oculars, illuminators, etc.), in which the spherical distortion is wholly 
or nearly eliminated, as in \ 12. Such pieces of apparatus are usually achromatic 
also. 
§ 14. Apochromatic Objectives.—A term used by Abbe to designate a new form 
of objectives made by combining new kinds of glass with a natural mineral (Cal- 
cium fluoride, Fluorite, or Fluor-spar). The name, Apochromatic, is used to in- 
dicate the higher kind of achromatism in which rays of three spectral colors are 
combined at one focus, instead of rays of two colors, as in the ordinary achromatic 
objectives. 
The special characteristics of these objectives, when used with the “compen- 
sating oculars” ($ 23), are as follows: 
(1) Three rays of different color are brought to one focus, leaving a small ter- 
tiary spectrum only, while with objectives as formerly made from crown and flint 
glass, only two different colors could be brought to the same focus. 
(2) In these objectives the correction of the spherical aberration is obtained for 
two different colors in the brightest part of the spectrum, and the objective shows 
the same degree of chromatic correction for the marginal as for the central part of 
the aperture. I11 the old objectives, correction of the spherical aberration was 
confined to rays of one color, the correction being made for the central part of the 
spectrum, the objective remaining under-corrected spherically for the red rays 
and tfzw-corrected for the blue rays. 
(3) The optical and chemical foci are identical, and the image formed by the 
chemical rays is much more perfect than with the old objectives, hence the new 
objectives are well adapted to photography. MICROSCOPE AND ACCESSORIES. 
5 
(4) These objectives admit of the use of very high oculars, and seem to be a 
considerable improvement over those made in the old way with crown and flint 
glass. According to Dippel (Z. w. M. 1886, p. 300), dry apochromatic objectives 
give as clear images as the same power water immersion objectives of the old form. 
§ 15. Non-Adjustable or Unadjustable Objectives.—Objectives in which the 
lenses or lens systems are permanently fixed in their mounting so that their rela- 
tive position always remains the same. Low power objectives and those with 
homogeneous immersion are mostly 11011-adjustable. For beginners and those un- 
skilled in manipulating adjustable (§ 16) objectives, nou-adjustable ones are more 
satisfactory, as the optician has put the lenses in such a position that the most 
satisfactory results may be obtained when the proper thickness of cover-glass and 
tube-length are employed. (See \ 17 and table and figure of tube-length and 
thickness of cover-glass below ) 
§ 16. Adjustable Objectives.—An adjustable objective is one in which the dis- 
tance between the systems of lenses (usually the front and the back systems) may 
be changed by the observer at pleasure. The object of this adjustment is to cor- 
rect or compensate for the displacement of the rays of light produced by the 
mounting medium and the cover-glass after.the rays have left the object. It is 
also to compensate for variations in “tube length.” See § 17. As the displace- 
ment of the rays by the cover-glass is the most constant and important, these ob- 
jectives are usually designated as having cover-glass adjustment or correction. 
(PI. II, Fig. 13. See also practical work, $ 63.) 
$ 17. Tube-Length and Thickness of Cover-Glasses.—“In the construction of 
microscopic objectives, the corrections must be made for the formation of the 
image at a definite distance, or in other words the tube of the microscope on 
which the objective is to be used must have a definite length. Consequently the 
microseopist must know and use this distance or ‘ microscopical tube-length’ to 
obtain the best results in using any objective in practical work.” Unfortunately 
different opticians have selected different tube-lengths and also different points 
between which the distance is measured, so that one must know what is meant by 
the tube-length of each optician whose objectives are used. See table. 
The thickness of cover-glass used on an object, (see Ch. V, on mounting), ex- 
cept with homogeneous immersion objectives, has a marked effect on the light 
passing from the object (PI. V, Fig. 41). To compensate for this the relative 
positions of the systems composing the objective are different from what they 
would be if the object were uncovered. Consequently, in non-adjustable objec- 
tives some standard thickness of cover-glass is chosen by each optician and the 
position of the systems arranged accordingly. With such an objective the image 
of an uncovered object would be less distinct than a covered one, and the same 
result would follow the use of a cover-glass much too thick (| 63, Fig. 41). 6 
MICROSCOPE AND ACCESSORIES. 
Length in Millimeters and Parts Included in “Tube-Length ” by 
Various Opticians.* 
Pts. included 
in “Tube- “Tube-length” in 
length.” Millimeters. 
See Diagram. 
' Grunow, New York 203 mm. 
Nachet et Fils, Paris 146 or 200 mm. 
Powell and Lealand, London .... 254 mm. 
C. Reichert, Vienna i6j to 180 mm. 
_ W. Wales, New York 254 mm. 
a-d 
b-d- 
Bausch & Loinb Opt. Co., Rochester .216 mm. 
B6zu, Hausser et Cie, Parisf 220 mm. 
Klonne und Miiller, Berlin 160-180 or 254 mm. 
W. & H. Seibert, Wetzlar 190 mm. 
Swift & Son, London 165 to 228 mm. 
C. Zeiss, Jena 160 or 250 mm. 
a-g . Gundlacli Optical Co., Rochester. . . 254 mm. 
a-g . R. Winkel, Gottingen 220 mm. 
c-d . Ross & Co., London 254 mm. 
c-e . R. & J. Beck, London 254 mm. 
c-g . H. R. Spencer & Co., Geneva, N. Y. . 254 mm. 
c-f . J. Green, Brooklyn J 254 mm. 
c'-e 
F. Leitz, Wetzlar 125-180 mm. 
For oil immersions 160 mm. 
Fig. 8b. 
Thickness of Cover Glass for which Non-Adjustable Objectives are Corrected 
by Various Opticians. 
'J. Green, Brooklyn. 
J. Grunow, New York. 
Powell and Lealand, London. 
H. R. Spencer & Co., Geneva, N. Y. 
W. Wales, New York. 
TO5?111111- 
Klonne und Muller, Berlin. 
F. Leitz, Wetzlar (when tube 160-170 mm.). 
xVomm- R. Winkel, Gottingen, Germany. 
1'm5mm. Ross & Co., London. 
Bausch & Lomb Optical Co., Rochester. 
C. Zeiss, Jena for apochromatic oil immersions), 
C. Reichert, Vienna. 
Gundlach Optical Co., Rochester. 
W. & H. Siebert, Wetzlar. 
R. & J. Beck, London. 
TUomm' 
Hur mm. J. Zentmayer, Philadelphia. 
10-12 54mm. 
THU 
f Nachet et Fils, Paris. 
L B£zu, Hausser et Cie, Paris. 
Swift & Son, London. 
§ 18. Aperture of Obje<5tives.—The angular aperture or angle of aperture of an 
objective is the angle “contained, in each case, between the most diverging of the 
rays issuing from the axial point of an object [i.e., a point in the object situated 
on the extended optic axis of the microscope], that can enter the objective and 
take part in the formation of an image.” (C.) 
* The information contained in these tables was very kindly furnished by the opticians named, 
f Successors to Hartnack. 
t Successor to Tolies. 7 
MICROSCOPE AND ACCESSORIES. 
According to some other authors the angle of aperture is the angle between the 
extreme rays from the focal point which can be transmitted through the entire 
objective. This would give a somewhat greater angle than by the first method as 
the focal point of the objective is nearer to it than the axial point of the object 
(PI. I, Fig. i, 3 and 5). 
In general, the angle increases with the size of the lenses forming the objective 
and the shortness of the equivalent focal distance ($ 7). If all objectives were dry 
or all water or homogeneous immersion a comparison of the angular aperture 
would give one a good idea of the relative number of image forming rays trans- 
mitted by different obj ectives ; but as some are dry, others water and still others 
homogeneous immersion, one can see at a glance (see PI. V, Fig. 42, 43, 44) that 
other things being equal, the dry objective (Fig. 42) receives less light than the 
water immersion, and the water immersion (Fig. 43) less than the homogeneous 
immersion (Fig. 44). In order to render comparison accurate between different 
kinds of obj ectives, Professor Abbe takes into consideration the rays actually pass- 
ing from the back combination of the objective to form the real image ; he thus 
takes into account the medium in front of the objective as well as the angular 
aperture. The term “ numerical aperture ” was introduced by Abbe to indicate 
the capacity of an optical instrument “for receiving rays from the object and 
transmitting them to the image, and the aperture of a microscopic objective is 
therefore determined by the ratio between its focal length and the diameter of the 
emergent pencil at the point of its emergence, that is the utilized diameter of a 
single-lens objective or of the back lens of a compound objective.” 
Numerical Aperture (abbreviated N.A.) is then the ratio of the diameter of the 
emergent pencil to the focal length of the lens, or as usually expressed, the factors 
being more readily obtainable, it is the index of refraction of the medium in front 
of the objective (i.e., air for dry, and water or homogeneous fluid for immersion 
objectives) multiplied by the sine of half the angle of aperture. The usual form- 
ula is N. A. = n sin u ; N.A. representing numerical aperture, n the index of refrac- 
tion of the substance in front of the objective, and u the semi-angle of aperture. 
For example, take three objectives each of 3 mm. equivalent focus, one being a 
dry, one a w7ater immersion, and one a homogeneous immersion. Suppose that 
the dry objective has an angular aperture of 106°, the water immersion of 940 and 
the homogeneous immersion of 90°. Simply compared as to their angular aper- 
ture, without regard to the medium in front of the objective, it would look as if 
the dry objective would actually take in and transmit a wider pencil of light than 
either of the others. However, if the medium in front of the objective is con- 
sidered, that is to say, if the numerical instead of the angular apertures are com- 
pared, the results would be as follows ; Numerical Aperture of a dry objective of 
1060, N.A. =11 sin u. In the case of dry objectives the medium in front of the 
objective being air the index of refraction is unity, whence n—1. Half the angular 
aperture is J-§-0 = 53°. By consulting a table of natural sines it will be found 
that the sine of 530 is 0.799, whence N.A. — sin n or 1 X sin u or 0.799 = 0.799. 
With the water immersion objective in the same way N. A. = « sin u. In this 
case the medium in front of the objective is water, and its index of refraction is 
1.33, whence 72 = 1.33. Half the angular aperture is -p° = A7°, and by consult- 
ing a table of natural sines, the sine of 470 is found to be 0.731 i.e. sin 72 = 0.731, 
whence N.A. =n or 1.33 X sin u or 0.731 =0.972. 
With the oil immersion in the same way N.A. —n sin u ; n or the index of refrac- 
tion of the homogeneous fluid in front of the objective is 1.52, and the semi-angle 8 
MICROSCOPE AND ACCESSORIES. 
of aperture is -9/° = 450. The sine of 450 is 0.707 whence N.A. — n or 1.52 X sin 
11 or o 707 = 1.074. 
By comparing these numerical apertures: Dry 0.799, water 0.972, homogene- 
ous immersion 1.074 the same idea of the real light efficiency and image power of 
the different objectives is obtained, as in the graphic representations shown in 
PI. V., Fig. 42, 43, 44. 
THE OCUEAR. 
\ 19. A Microscopic Ocular or Eye-Piece consists of one or more converging 
lenses or lens systems, the combined action of which is, like that of a simple mi- 
croscope, to magnify the real image formed by the objective. 
Depending upon the relation and action of the different lenses forming oculars, 
they are divided into two great groups, negative and positive. 
20. Negative Oculars, are those in which the real, inverted image is formed 
within the ocular, the lower or field-lens serving to collect the image-forming rays 
somewhat so that the real image is smaller than as if the field-lens were absent 
(PI. I, Fig. 6). As the field-lens of the ocular aids in the formation of the real 
image it is considered by some to form a part of the objective rather than of the 
ocular. The upper or eye-lens of the ocular magnifies the real image. 
\ 21. Positive Oculars are those in which the real, inverted image of the object- 
ive is formed outside the ocular, and the entire system of ocular lenses magnifies 
the real image like a simple microscope (PI. I, Fig. 5). 
Positive and negative oculars may be readily distinguished, as a positive ocular 
may be used as a simple microscope, while a negative ocular cannot be so used 
when its field glass is in the natural position toward the object. By turning the 
eye-lens toward the object and looking into the field-lens an image may be seen, 
however. 
Special names have also been applied to oculars, depending upon the designer, 
the construction, or the special use to which the ocular is to be applied. The fol- 
lowing are used in the anatomical department of Cornell University :—* 
works and catalogues concerning the microscope and microscopic apparatus, 
and in articles upon the microscope in periodicals, various forms of oculars or eye- 
pieces are so frequently mentioned, without explanation or definition, that it 
seemed 'worth while to give a list, with the French and German equivalents, and 
a brief statement of their character. 
Achromatic Ocular; Fr. oculaire achromatique; Ger. achromatisches Okular. 
Oculars in which chromatic aberration is wholly or nearly eliminated. Aplanatic 
Ocular; Fr. Oculaire aplanatique; Ger. aplauatisches Okular (see $ 13). Bi- 
nocular, stereoscopic Ocular ; Fr. Oculaire binoculaire stereoscopique ; Ger. stere- 
oskopisches Doppel-Okular. An ocular consisting of two oculars about as far 
apart as the two eyes. These are connected with a single tube which fits a monoc- 
ular microscope. By an arrangement of prisms the image forming rays are divided, 
half being sent to each eye. The most satisfactory form was worked out by 
Tolies and is constructed on true stereotomic principles, both fields being equally 
illuminated. His ocular is also erecting. CampanVs Ocular (See Huygenian 
Ocular). Compound Ocular ; Fr. Oculaire composd ; Ger. zusammengesetztes Ok- 
ular. An ocular of two or more lenses, e. g., the Huygenian (see Fig. 5 and 6). 
Deep Ocular, see high ocular. Erecting Ocular; Fr. Oculaire redresseur; Ger. 
bildumkehrendes Okular. An ocular with which an erecting prism is connected 9 
MICROSCOPE AND ACCESSORIES. 
| 22. Huygenian Ocular.—A negative ocular designed by Huygens for the tel- 
escope, but adapted also to the microscope. It is the one now most commonly 
employed. It consists of a field-lens or collective (Pi. I, Fig. 6), aiding the ob- 
jective in forming the real image, and an eye-lens which magnifies the real image. 
While the field-lens aids the objective in the formation of the real, inverted im- 
age, and increases the field of view ; it also combines with the eye-lens in ren- 
dering the image achromatic ($ 35). 
§ 23. Compensating Oculars.—These are oculars specially constructed for use 
with the apochromatic objectives. They compensate for aberrations outside the 
axis which could not be so readily eliminated in the objective itself. Oculars of 
this kind, magnifying but once or twice, are made for use with high powers, for 
the sake of the large field in finding objects ; they are called searching oculars ; 
those ordinarily used for observation are in contradistinction called working ocu- 
lars. Part of the compensating oculars are positive and part negative. 
| 24. Projection Oculars.—These are oculars especially designed for projecting 
a microscopic image on the screen for class demonstrations, or for photographing 
so that the image is erect as with the simple microscope. Such oculars are most 
common on dissecting microscopes. Goniometer Ocular; Fr. Oculaire a gonio- 
metre ; Ger. Goniometer-Okular. An ocular with goniometer for measuring the 
angles of minute crystals. High Ocular, sometimes called a deep ocular. One 
that magnifies the real image considerably, i. e., io to 20 fold. Huygenian Ocu- 
lar, Huygens’ O., Campani’s O. ; Fr. Oculaire d’Huygens, o. de Campani; Ger. 
Huygens’sches Okular, Campaniches Okular, see $ 22. Kellner's Ocular, see 
orthoscopic ocular. Low Ocular, also called shallow ocular. A11 ocular which mag- 
nifies the real image only moderately, i. e., 2 to 8 fold. Micrometer or micromet- 
ric Ocular; Fr. Oculaire micrometrique or a micrometre ; Ger. Mikrometer-Oku- 
lar, see $ 25. Microscopic Ocular; Fr. Oculaire microscopique; Ger. Mikroskop- 
isches Okular. An ocular for the microscope instead of one for a telescope. 
Negative Ocular, see \ 21. Orthoscopic Oculars ; also called Kellner’s Ocular ; Fr. 
Oculaire orthoscopique ; Ger. Kellner’sches oder Orthoskopisches Okular. An 
ocular with an eye-lens like one of the combinations of an objective (PI. II, Fig. 
12, 13) and a double convex field-lens. The field-lens is in the focus of the eye- 
lens and there is no diaphragm present. The field is large and flat. Periscopic 
Ocular; Fr. Oculaire periscopique ; Ger. Periskopisches Okular. A positive ocu- 
lar devised by Gundlach. It consists of a double convex field-lens and a triplet 
eye-lens. It gives a large fiat field. Positive Ocular, see $ 21. Projection Ocu- 
lar ; Ger. Projections-Okular, see \ 24. Ramsden's Ocular ; Fr. Oculaire de Rams- 
den ; Ger. Ramsdeu’sclies Okular. A positive ocular devised by Ramsden. It 
consists of two plano-convex lenses placed close together with the convex sur- 
faces facing each other. Only the central part of the field is clear. Searching 
Ocular; Ger. Sucher-Okular, see § 23. Shallow Ocular, see low ocular. Solid 
Ocular, holosteric O. ; Fr. Oculaire holostere ; Ger. Holosterisclies Okular, Voll- 
glass-Okular. A negative eye-piece devised by Tolies. It consists of a solid piece 
of glass with a moderate curvature at one end for a field-lens, and the other end 
with a much greater curvature for an eye-lens. For a diaphragm, a groove is cut 
at the proper level and filled with black pigment. It is especially excellent 
where a high ocular is desired. Spectral or spectroscopic Ocular; Fr. Oculaire 
spectroscopique ; Ger. Spectral-Okular, see Microspectroscope, Ch. IV. Working 
Ocular; Ger. Arbeits-Okular, see g 23. 10 
MICROSCOPE AND ACCESSORIES. 
with the microscope. While they are specially adapted for use with apochromatic 
objectives, they may also be used with ordinary achromatic objectives of large 
numerical aperture. 
§ 25. Micrometer Ocular.—This is an ocular connected with an ocular microme- 
ter. The micrometer may be removable, or it may be permanently in connection 
with the ocular, and arranged with a spring and screw, by which it may be moved 
back and forth across the field. (See Ch. Ill, under Micrometry). 
§ 26. Spedtral or Specftroscopic Ocular.—(See Micro-Spectroscope, Ch. IV). 
DESIGNATION OF OCULARS. 
$ 27. Equivalent Focus.—As with objectives some opticians designate the ocu- 
lars by their equivalent focus (§ 7). With this method the power of the ocular 
varies inversely with the focal length, i. e., the less the equivalent focus the greater 
the power, and the greater the focal length the lower the power. 
I 28. Numbering and Lettering.—Oculars like objectives may be numbered or 
lettered arbitrarily. When so designated, the smaller the number, or the earlier 
the letter in the alphabet, the lower the power of the ocular. 
$ 29. Magnification or Combined Magnification and Equivalent Focus.—The 
compensating oculars are marked both with their equivalent focus and the amount 
they magnify the real image. Thus, an occular marked x4, 45 mm., indicates 
that the equivalent focus is 45 milimeters, and that the real image of the objective 
is multiplied four-fold by the ocular. 
The projection oculars are designated simply by the amount they multiply the 
real image of the objective. Thus for the short or 160 mm. tube-length they are, 
x 2, x 4 ; and for the long, or 250 mm. tube, they are x 3 and x 6. That is, the 
final image on the screen or the ground glass of the photographic camera will be 
2, 3, 4, or 6 times greater than it would be if no ocular were used. 
COMPOUND MICROSCOPE. 
EXPERIMENTS 
§ 30- Putting an Objective in Position and Removing it. —Ele- 
vate the body of the microscope by means of the coarse adjustment 
(Fig. io), so that there may be plenty of room between its lower end 
and the stage. Grasp the objective lightly near its lower end with two 
fingers of the left hand, and hold it against the nut in the lower end of 
the body (Fig. io). With two fingers of the right hand take hold of 
milled ring near the back or upper end of the objective, and screw it 
into the body of the microscope. Reverse this operation for removing 
the objective. By following this method the danger of dropping the 
objective will be avoided. 
§ 31. Putting an Ocular in Position and Removing it.—Elevate 
the body of the microscope with the coarse adjustment (Fig. 10), so that 
the objective will be 2 cm. or more from the object—grasp the ocular 
by the milled ring next the eye-lens (Fig. 5), and the coarse adjust- 
ment or the tube of the microscope and gently force the ocular into MICROSCOPE AND ACCESSORIES. 
11 
position. In removing the ocular, reverse the operation. If the above 
precautions are not taken, and the oculars fit snugly, there is danger in 
inserting them of forcing the body of the micro- 
scope downward and the objective upon the object. 
§ 32. Putting an Object under the Micro- 
scope.—This is so placing an object under the 
simple microscope, or on the stage of the com- 
pound microscope, that it will be in the field of 
view when the microscope is in focus (§ 33). 
With low powers, it is not difficult to get an ob- 
ject under the microscope. The difficulty increases, 
however, with the power of the microscope and the 
smallness of the object. It is usually necessary to 
move the object in various directions while look- 
ing into the microscope, in order to get it into the 
field. Time is usually saved by getting the object 
in the center of the field with a low objective be- 
fore putting the high objective in position. This 
is greatly facilitated by using a double nose-piece, 
or revolver.* 
§ 33. Field or Field of View of a Micro- 
scope.—The area visible through a microscope 
when it is in focus. When properly lighted, and there is no object un- 
der the microscope, the field appears as a circle of light. When exam- 
ining an object it appears within the light circle, and by moving the ob- 
ject, if it is of sufficient size, different parts are brought successively 
into the field of view. 
In general, the greater the magnification of the entire microscope, 
whether the magnification is produced mainly by the objective, the 
ocular, or by increasing the tube-length, or by a combination of all 
three (see Ch. Ill, under magnification), the smaller is the field. 
The size of the field is also dependent, in part, without regard to 
magnification, upon the size of the opening in the ocular diaphragm. 
Fig. 17.—Double Nose-Piece 
or Revolver for Quickly 
Changing Two Objectives. 
* As specimens are sometimes very small, or some part of a large specimen 
shows a particular structure with special excellence, it is desirable to mark the 
preparation so that the minute object or the part of a large object may be found 
quickly and with certainty. A simple way to do this is to find the object under 
the microscope, and then place a minute spot of black ink at one side. After this 
is done, remove the slide from the stage and surround the object with a ring of 
shellac cement, making the ring as small as possible and not cover the object. It 
will then always be known that the part to be examined is within the ring (B. i, 
47, C. 117). The enclosure in a ring may also be very elegantly done by the use 
of a marking apparatus like that of Winkel’s (B. K. & S., p. 48), making use of 
either a diamond point or a delicate brush dipped in shellac or other cement. 12 
MICROSCOPE AND ACCESSORIES. 
Some oculars, as the orthoscopic and periscopic, are so constructed as to 
eliminate the ocular diaphragm, and in consequence, although this is 
not the sole cause, the field is considerably increased. The exact size 
of the field may be read off directly by putting a stage micrometer 
under the microscope and noting the number of spaces required to meas- 
ure the diameter of the light circle. 
The size of the field of the microscope as projected into the field of 
vision of the normal human eye (i. e., the virtual image) may be de- 
termined by the use of the camera lucida with the drawing surface 
placed at the standard distance of 250 millimeters (Ch. III). 
FUNCTION OF AN OBJECTIVE. 
§ 34- Put a 2-in. (50 mm.) objective on the microscope, or screw off 
the front combination of a (18 min.), and put the back-combina- 
tion on the microscope for a low objective. 
Place some printed letters or figures under the microscope, and light 
well. In place of an ocular, put a screen of ground glass, or a piece of 
Japanese or tissue paper, over the upper end of the body of the micro- 
scope.* 
Lower the body by means of the coarse adjustment (Fig. 10), until 
the objective is within 2-3 cm. of the object on the stage. Look at the 
screen on the top of the body, holding the head about as far from it as 
for ordinary reading, and slowly elevate the body by means of the 
coarse adjustment until the image of the letters appears on the screen. 
The image can be more clearly seen if the object is in a strong light 
and the screen in a moderate light, i. e., if the top of the microscope is 
shaded. 
The letters will appear as if printed on the ground glass or paper, but 
will be inverted (Fig. 5). 
If the objective is not raised sufficiently, and the head is held too near 
the microscope, the objective will act as a simple microscope. If the 
letters are erect, and appear to be down in the microscope and not on 
the screen, hold the head farther from it, shade the latter, and raise the 
body of the microscope until the letters do appear on the screen. 
To demonstrate that the object must be outside the principal focus 
with the compound microscope, remove the screen and turn the tube of 
the microscope directly toward the sun. Move the tube of the micro- 
scope with the coarse adjustment until the burning or focal point is 
* Ground glass may be very easily prepared by placing some fine emery between 
two pieces of glass, wetting it with water and then rubbing the glasses together for 
a few minutes. If the glass becomes too opaque, it may be rendered more trans- 
lucent by rubbing some oil upon it. 13 
MICROSCOPE AND ACCESSORIES. 
found (§ 4). Measure the distance from the paper object on the stage 
to the objective, and it will represent approximately the principal focal 
distance (PI. I, Fig. 1). Replace the screen over the top of the tube, 
no image can be seen. Slowly raise the tube of the microscope and the 
image will finally appear. If the distance between the object and the 
objective is now taken, it will be found considerably greater than the 
principal focal distance (compare § 4). 
Aerial Image.—After seeing the real image on the ground-glass, or 
paper, use the Japanese paper over about half of the opening of the 
tube of the microscope. Hold the eye about 250 mm. from the micro- 
scope as before and shade the top of the tube by holding the hand be- 
tween it and the light, or in some other way. The real image can be 
seen in part as if on the paper and in part in the air. Move the paper so 
that the image of half a letter will be on the paper and half in the air. 
Another striking experiment is to have a small hole in the paper 
placed over the center of the tube opening, then if a printed word ex- 
tends entirely across the diameter of the tube its central part may be 
seen in the air, the lateral parts on the paper. The advantage of the 
paper over part of the opening is to enable one to accommodate the 
eyes for the right distance. If the paper is absent the eyes adjust 
themselves for the light circle at the back of the objective, and the 
aerial image appears low in the tube. Furthermore, it is more diffi- 
cult to see the aerial image in space than to see the image on the 
ground-glass or paper, for the eye must be held in the right position to 
receive the rays projected from the real image, while the granular sur- 
face of the glass and the delicate fibers of the paper reflect the rays ir- 
regularly, so that the image may be seen at almost any angle, as if the 
letters were actually printed on the paper or glass. 
The function of an objective, as seen from these experiments, is to 
form an enlarged, inverted, real image of an object, this image being 
formed on the opposite side of the objective from the object (Fig. 5). 
FUNCTION OF AN OCULAR. 
§ 35- Using the same objective as for § 34, get as clear an image of 
the letters as possible on the Japanese paper screen. Look at the 
image with a simple microscope (Fig. 8 or 9) as if the image were an 
object. Observe that the image seen through the simple microscope 
is merely an enlargement of the one on the screen, and that the letters 
remain inverted, that is they appear as with the naked eye (§ 4). 
Remove the screen and observe the aerial image with the tripod. 
Put an A, No. 1, 2 in. or 45 mm. ocular (i. e., an ocular of low mag- 
nification) in position (§ 31). Hold the eye about 10 to 20 millimeters 
from the eye-lens and look into the microscope. The letters will ap- 14 
MICROSCOPE AND ACCESSORIES. 
pear as when the simple microscope was used (see above), the image 
will become more distinct by slightly raising the body of the micro- 
scope with the coarse adjustment. 
The function of the Ocular, as seen from the above, is that of a 
simple microscope, viz.: It magnifies the real image formed by the ob- 
jective as if that image were an object. Compare the image formed 
by the ocular (Fig. 5), and that formed by a simple microscope (Fig. 4). 
It should be borne in mind, however, that the rays from an object as 
usually examined with a simple microscope, extend from the object in 
all directions, and no matter at what angle the simple microscope is 
held, provided it is sufficiently near and points toward the object, an 
image may be seen. The rays from a real image, however, are con- 
tinued in certain definite lines and not in all directions ; hence, in 
order to see the image with an ocular or simple microscope, or in order 
to see the aerial image with the unaided eye, the simple microscope, 
ocular or eye must be put in the path of the rays. 
The field-lens of a Huygenian ocular makes the real image smaller 
and consequently increases the size of the field ; it also makes the im- 
age brighter by contracting the area of the real image (PI. I, Fig. 6). 
Demonstrate this by screwing off the field-lens and using the eye-lens 
alone as in the ocular, refocusing if necessary. Note also that the let- 
ters or other image is bordered by a colored haze (§ 22). 
When looking into the ocular with the field-lens removed, the eye 
should not be held so close to the ocular, as the eye-point is consider- 
ably farther away than when the field-lens is in place (PI. I, Fig. 7, 
and § 36). 
§ 36. The Eye-Point.—This is the point above an ocular or simple 
microscope where the greatest number of emerging rays cross. Seen 
in profile, it may be likened to the narrowest part of an hour-glass. 
Seen in section (PI. I, Fig. 7), it is the smallest and brightest light 
circle above the ocular. This is called the eye-point, for if the pupil 
of the eye is placed at this level, it will receive the greatest number of 
rays from the microscope, and consequently see the largest field. 
Demonstrate the eye-point by having in position an objective and 
ocular as above (§ 35). Tight the object brightly, focus the micro- 
scope, shade the ocular, then hold some ground-glass or a piece of 
the Japanese paper (§ 72) above the ocular and slowly raise and lower 
it until the smallest circle of light is found. By using different oculars 
it will be seen that the eye-point is nearer the eye-lens in low than in 
high oculars. 15 
MICROSCOPE AND ACCESSORIES. 
LIGHTING AND FOCUSING. 
§ 37. Focusing is mutually arranging an object and the microscope so that a 
clear image may be seen. 
With a simple microscope (§ 4) either the object or the microscope or both may 
be moved in order to see the image clearly, but with the compound microscope 
the object more conveniently remains stationary on the stage, and the tube or 
body of the microscope is raised or lowered (PI. II, Fig. 10). 
In general, the higher the power of the whole microscope whether simple or 
compound, the nearer together must the object and objective be brought. With 
the compound microscope, the higher the objective, and the longer the body of the 
microscope, the nearer together must the object and the objective be brought. If 
the oculars are not par-focal (£ 48), the higher the magnification of the ocular, the 
nearer must object and objective be brought. 
$ 38. Working Distance.—By this is meant the space between the simple mi- 
croscope and the object, or between the front-lens of the compound microscope 
and the object, when the microscope is in focus. This working distance is always 
considerably less than the equivalent focal length of the objective. For example, 
the front-lens of a Xth in., or 6 mm. objective would not be %t\\ inch, or 6 milli- 
meters from the object when the microscope is in focus, but considerably less than 
that distance. If there were no other reason than the limited working distance of 
high objectives, it would be necessary to use very thin cover glasses over the ob- 
ject. (See \ 16, 17). If too thick covers are used, it may be impossible to get an 
objective near enough an object to get it in focus. For objects that admit of ex- 
amination with high powers it is always better to use thin covers. 
FOCUSING. 
LIGHTING. 
§ 39- Unmodified sunlight should not be employed except in special cases. 
North light is best and most uniform. When the sky is covered with white 
clouds the light is most favorable. The light should come from the left; but if 
it is necessary to face the window a vertical, adjustable screen between the face 
and the window is desirable. If artificial illumination must be employed, use a 
lamp that gives a brilliant and steady light ($ 57). 
It is of the greatest importance and advantage for one who is to use the micro- 
scope for serious work that he should comprehend and appreciate thoroughly the 
various methods of illumination, and the special appearances due to different 
kinds of illumination. 
Depending on whether the light illuminating an object traverses the object or 
is reflected upon it, and also whether the object is symetrically lighted, or lighted 
more on one side than the other, light used in microscopy is designated as re- 
flected and transmitted, axial and oblique. 
\ 40. Reflected, Incident or Direct Light.—By this is meant light reflected upon 
the object in some way and then irregularly reflected from the object to the mi- 
croscope. By this kind of light objects are ordinarily seen by the unaided eye, 
attd the objects are mostly opaque. Invertebrate Histology (Part II), reflected 
light is but little used; but in the study of opaque objects, like whole insects, 
etc., it is used a great deal. For low powers, ordinary daylight that naturally 
falls upon the object, or is reflected or condensed upon it with a mirror or con- 16 
MICROSCOPE AND ACCESSORIES. 
densing lens, answers very well. For high powers and for special purposes, 
special illuminating apparatus has been devised (Fig. 12). (See Carpenter). 
\ 41. Transmitted Light.—By this is meant light which passes through an ob- 
ject from the opposite side. The details of a photographic negative are in many 
cases only seen or best seen by transmitted ligbt, while the print made from it is 
best seen by reflected light (§ 40). 
Almost all objects studied in Vertebrate Histology are lighted by transmitted 
light, and they are in some way rendered transparent or semi-transparent. The 
light traversing and serving to illuminate the object in working with a compound 
microscope is usually reflected from a plane or concave mirror, or from a mirror 
to an illuminator ($ 54), and thence transmitted to the object from below (PI. 
II, Fig. 10, 13 ; PI. Ill, Fig. 20). 
\ 42. Axial or Central Light.—By this is understood light reaching the object, 
the rays of light being parallel to each other and to the optic axis of the micro- 
scope, or a diverging or converging cone of light whose axial ray is parallel with 
the optic axis of the microscope. In either case the object is symmetrically 
illuminated. 
£ 43. Oblique Light. This is light in which parallel rays from a plane mirror 
form an angle with the optic axis of the microscope (PL II, Fig. 12, 13 c). Or 
if a concave mirror or a condenser is used, the light is oblique when the axial 
ray of the cone of light forms an angle with the optic axis (PI. Ill, Fig. 20a). 
DIAPHRAGMS. 
I 44. Diaphragms and their Proper Employment.—Diaphragms are opaque 
disks with openings of various sizes, which are placed between the source of light 
or mirror and the object. In some cases an iris diaphragm is used, and then the 
same one is capable of giving a large range of openings. The object of a dia- 
phragm, in general, is to cut off all adventitious light and thus to enable one to light 
the object in such a way that the light finally reaching the microscope shall all 
come from the object or its immediate vicinity. 
\ 45. Size and Position of Diaphragm Opening.—The size of the opening in the 
diaphragm should be about that of the front lens of the objective used. For 
some objects and some objectives this rule may be quite widely departed from ; 
one must learn by trial. 
When lighting with a mirror the diaphragm should be as close as possible to the 
object in order, (a) that it may exclude all adventitious light from the object; (b) 
that it may not interfere with the most efficient illumination by the mirror by 
cutting off a part of the illuminating pencil. If the diaphragm is a considerable 
distance below the object, (1) it allows considerable adventitious light to reach 
the object and thus injures the distinctness of the microscopic image; (2) it pre- 
vents the use of very oblique light unless it swings with the mirror; (3) it cuts off 
a part of the illuminating cone from a concave mirror (Fig. n). 
With an illuminator (PI. Ill, Fig. 20), the diaphragm serves to narrow the pen- 
cil to be transmitted through the condenser, and thus to limit the aperture 
or for any special purpose to be served (see \ 61). Furthermore, by 
making the diaphragm opening excentric, oblique light may be used, or by using 
a diaphragm with a slit around the edge (central stop diaphragm), the center re- 
maining opaque, the object may be lighted with a hollow cone of light all of the 
rays having great obliquity. In this way the so-called dark-ground illumination 
may be produced ($ 60; PI. Ill, Fig. 20). 17 
MICROSCOPE AND ACCESSORIES. 
LIGHTING AND FOCUSING : EXPERIMENTS- 
§ 46. Lighting with a Mirror.—Put a mounted fly’s wing (see Cli. 
V, under mounting), under the microscope, put the in. (18 mm..) or 
other low objective in position, also a low ocular. With the coarse ad- 
justment (Fig. 10), lower the body of the microscope within about 1 
cm. of the object. Use an opening in the diaphragm about as large as 
the front lens of the objective ; then with the plane mirror try to reflect 
light up through the diaphragm upon the object. One can tell when 
the field (§ 33) is illuminated, by looking at the object on the stage, but 
more satisfactorily by looking into the microscope. It sometimes re- 
quires considerable manipulation to light the field well. After using 
the plane side of the mirror turn the concave side into position and light 
the field with it. A.s the concave mirror condenses the light, the field 
will look brighter with it than with the plane mirror. Is it especially 
desirable to remember that the excellence of lighting depends in part 
on the position of the diaphragm (§ 45). If the greatest illumination 
is to be obtained from the concave mirror, its position must be such that 
its focus will be at the level of the object. This distance can be very 
easily determined by finding the focal point of the mirror in full sun- 
light. 
§ 47. Use of the Plane and of the Concave Mirror.—The mirror 
should be freely movable, and have a plane and a concave face. The 
concave face is used when a large amount of light is needed, the plane 
face when a moderate amount is needed or when it is necessary to have 
parallel rays or to know the direction of the rays. 
§ 48. Focusing with Low Objectives.—Place a mounted fly’swing 
under the microscope ; put the three-fourths (18 mm.) objective in po- 
sition, and also the lowest ocular. Select the proper opening in the 
diaphragm and light the object well with transmitted light (§41, 48). 
Hold the head at about the level of the stage, look toward the win- 
dow, and between the object ahd the front of the objective ; with the 
coarse adjustment lower the body (Fig. 10), until the objective is within 
about half a cm. of the object. Then look into the microscope and 
slowly elevate the body with the coarse adjustment. The image will 
appear dimly at first, but will become very distinct by turning the body 
still higher. If the body is raised too high the image will become in- 
distinct, and finally disappear. It will again appear if the body is 
lowered the proper distance. 
When the microscope is well focused try both the concave and the 
plane mirrors, in various positions and note the effect. Put a high oc- 
ular in place of the low one (§ 27, 29, 31). If the oculars are not par- 18 
MICROSCOPE AND ACCESSORIES. 
focal it will be necessary to lower the tube somewhat to get the image 
in focus.* 
Pull out the draw-tube (Fig. io) 4-6 cm., thus lengthening the body 
of the microscope, and it will be found necessary to lower the tube of 
the microscope somewhat. 
§ 49. Pushing in the Draw-Tube.—To push in the draw-tube, 
grasp the large milled ring of the ocular with one hand, and the milled 
head of the coarse adjustment with the other, and gradually push the 
draw-tube into the tube. If this were done without these precautions 
the objective might be forced against the object and the ocular thrown 
out by the compressed air. 
§50. Focusing with High Objectives.—Employ the same object 
as before, elevate the body of the microscope and remove the in. 
(18 mm.) objective as indicated. Put the in., (5 mm.) or a higher 
objective in place, and use a low ocular. 
Eight well, and employ the proper opening in the diaphragm, etc. 
(§ 45). Look between the front of the objective and the object as be- 
fore (§ 48), and lower the body with the coarse adjustment till the ob- 
jective almost touches the cover-glass over the object. Look into the 
microscope, and, with the coarse adjustment, raise the body very slowly 
until the image begins to appear, then turn the milled head of the fine 
adjustment (Fig. 10), first one way and then the other, if necessary, 
until the image is sharply defined. 
Note that this high objective must be brought nearer the object than 
the low one, and that by changing to a higher ocular, if the oculars 
are not par-focal, or lengthening the body it will be found necessary 
to bring the objective still nearer the object, as with low objective 
(§ 48). 
§ 51. Always Focus Up, as directed above. If one lowers the body 
only when looking at the end of the objective as directed above, there 
will be no danger of bringing the objective in contact with the object, 
as may be done if one looks into the microscope and focuses down. 
When the instrument is well focused, move the object around in order 
to bring different parts into the field of view (§ 33). It may be neces- 
sary to re-focus with the fine adjustment every time a different part is 
brought into the field. In practical work, one hand is kept on the fine 
adjustment constantly, and the focus is continually varied. 
* Par-focal oculars are so constructed, or so mounted, that those of different 
powers may be interchanged without the microscopic image becoming wholly out 
of focus. When high objectives are used, while the image may be seen after 
changing oculars, the instrument nearly always needs slight focusing. With low 
powers this may not be necessary. 19 
MICROCSOPE AND ACCESSORIES. 
CENTRAL and OBLIQUE LIGHT WITH A MIRROR. 
§ 52. Axial Light, (§ 42).—Place a preparation containing minute 
air-bubbles under the microscope. (The preparation may be easily 
made by beating a drop of mucilage on a slide and covering it. See 
Ch. II). Use a inch (3 mm.) or No. 7 objective, and a medium 
ocular. Remove all the diaphragms and the sub-stage. Focus the 
microscope and select a very small bubble, one whose image appears 
about 1 nun. in diameter, then arrange the plane mirror so that the 
light spot in the bubble appears exactly in the center. Without chang- 
ing the position of the mirror in the least, replace the air-bubble pre- 
paration by one of Pleurasigma angulatum or some other finely marked 
diatom. Study the appearance very carefully. 
§ 53. Oblique Light, (§ 43).—Swing the mirror far to one side so 
that the rays reaching the object may be very oblique to the optic axis 
of the microscope. Study carefully the appearance of the diatom with 
the oblique light. Compare the different appearance with that of central 
light. The effect of oblique light is not so striking with histological 
preparations as with diatoms. 
It should be especially noted in §§ 52, 53, that one cannot determine 
the exact direction of the rays by the position of the mirror. This is 
especially true for axial light, (§ 52). To be certain that the light is 
axial some such test as that given in § 52 should be applied. (See also 
Ch. II, under Air-bubbles). 
ABBE IEEUMINATOR OR CONDENSER. 
§ 54- For all powers; but especially for high power objectives, a con- 
denser or illuminator is of great advantage. The one most generally 
useful was designed by Abbe. It consists of two or three very large 
lenses which are placed in some form of mounting beneath the stage. 
It serves to concentrate a very wide pencil of light from the mirror 
upon the object. For the best work in modern histology the Abbe il- 
luminator is almost as indispensable as the homogeneous immersion 
objectives (PI. Ill, Fig. 20). 
§ 55. Centering and Arrangement of the Illuminator.—The 
proper position of the illuminator for high objectives is one in which 
the beam of light traversing it is brought to a focus on the object. If 
parallel rays are reflected from the plane mirror to it, they will be 
focused only a few millimeters above the upper lens of the illuminator ; 
consequently the illuminator should be about on the level of the top of 
the stage and therefore almost in contact with the lower surface of the 
slide. For some purposes, when it is desirable to avoid the loss of light 
by reflection or refraction, a drop of water or homogeneous immersion 20 
MICROSCOPE AND ACCESSORIES. 
fluid is put between the slide and condenser, forming the so-called 
immersion illuminator. This is necessary only with objectives of 
high power and large aperture or for dark-ground illumination. 
Centering the Illuminator.—The illuminator should be centered to 
the optic axis of the microscope, that is the optic axis of the condenser 
and of the microscope should coincide. If one has a pin-hole dia- 
phragm to put over the end of the condenser (Fig. 20)—that is a dia- 
phragm with a small central hole—the central opening should appear 
to be in the middle of the field of the microscope. If it does not, the 
condenser should be moved from side to side by loosening the center- 
ing screws until it is in the center of the field. In case no pin-hole 
diaphragm accompanies the condenser, one may put a very small drop 
of ink, as from a pen-point, on the center of the upper lens and look at 
it with the microscope to see if it is in the center of the field. If it 
is not, the condenser should be adjusted until it is. The microscope 
and illuminator axes may not be entirely coincident even when the cen- 
ter of the upper lens appears in the center of the field, as there may be 
some lateral tilting of the condenser, but the above is the best the ordi- 
nary worker can do, and unless the mechanical arrangements of the 
illuminator are very deficient, it will be very nearly if not absolutely 
centered. 
§ 56. Mirror and Light for the Abbe Illuminator.—It is best to 
use daylight for this as for all other means of illumination. The rays 
of daylight are practically parallel, and it is best, therefore, to employ 
the plane mirror for all but the lowest powers. If low powers are used 
the whole field might not be illuminated with the plane mirror and the 
condenser close to the object; furthermore, the image of the window 
frame, objects outside the building, as trees, etc., would appear with 
unpleasant distinctness in the field of the microscope. To overcome 
these defects, one can lower the condenser and thus light the object 
with a diverging cone of light, or use the concave mirror and attain 
the same end when the condenser is close to the object (PI. Ill, 
Fig. 20). 
§ 57. Lamplight.—If one must use lamplight, it is recommended 
that a large condensing lens be placed in such a position between the 
light and the mirror that a picture of the lamp flame is thrown upon the 
mirror. If one does not have a condensing lens the concave mirror may 
be used to render the rays less divergent. It may be necessary to lower 
the illuminator somewhat in order to illuminate the object in its focus. 
ABBE ILLUMINATOR : EXPERIMENTS. 
§ 58. Abbe Illuminator, Axial and Oblique Light.—Use a dia- 
phragm a little larger than the front lens of the yi (3 nun.) or No. 7 21 
MICROSCOPE AND ACCESSORIES. 
objective, have the illuminator on the level or nearly on the level of the 
upper surface of the stage, and use the plane mirror. Be sure that the 
diaphragm carrier is in the notch indicating that it is central in position. 
Use the Pleurasigma as object. Study carefully the appearance of the 
diatom with this central light, then make the diaphragm excentric so 
as to light with oblique light. The differences in appearance will prob- 
ably be even more striking than with the mirror alone (§§ 52, 53). 
§ 59. Lateral Swaying of the Image.—Frequently in studying an 
object, especially with a high power, it will appear to sway from side 
to side in focusing up or down. A glass stage micrometer or fly’s wing 
is an excellent object. Make the light central or axial and focus up 
and down and notice that the lines simply disappear or grow dim. Now 
make the light oblique, either by making the diaphragm opening excen- 
tric or if simply a mirror is used, by swinging the mirror sidewise. On 
focusing up and down, the lines will sway from side to side. What is 
the direction of apparent movement in focusing down with reference to 
the illuminating ray ? What in focusing up ? If one understands this 
experiment it may sometime save a great deal of confusion. 
§ 60. Dark-Ground Illumination.—When an object is lighted with 
rays of a greater obliquity than can get into the front-lens of the objec- 
tive, the field will appear dark (PI. Ill, Fig. 22). If now the ob- 
ject is composed of fine particles, or is semi-transparent, it will refract 
or reflect the light which meets it, in such a way that a part of the very 
oblique rays will pass into the objective, hence as light reaches the ob- 
jective only from the object, all the surrounding field will be dark and 
the object will appear like a self-luminous one on a dark back ground. 
This form of illumination is only successful with low powers and objec- 
tives of small aperture. It is well to make the illuminator immersion 
for this experiment, see § 55. 
(A) With the Mirror.—Remove all the diaphragms so that very 
oblique light may be used, employ a stage micrometer in which the 
lines have been filled with graphite, use a (18 mm.) or No. 4 
objective, and when the light is sufficiently oblique the lines will ap- 
pear something like streaks of silver on a black back-ground. A 
specimen like that described below in (B) may also be used. 
(B) With the Abbe Illuminator.—Have the illuminator so that the 
light would be focused on the object (see above § 55) and use a dia- 
phragm with the slit opening ; employ the same objective as in (A). 
For object place a drop of a 10% solution of salicylic acid in alcohol 
on the middle of a slide and allow it to dry and crystallize. The crys- 
tals will appear brilliantly lighted on a dark back-ground. Put in an 
ordinary diaphragm and make the light oblique by making the dia- 
phragm eccentric. The same specimen may also be tried with a 22 
MICROSCOPE AND ACCESSORIES. 
mirror and oblique light. In order to appreciate the difference between 
this dark ground and ordinary transmitted light illumination, use an 
ordinary diaphragm and observe the crystals. 
A very striking and instructive experiment may be made by adding 
a very small drop of the solution to the dried preparation, putting it 
under the microscope very quickly, lighting for dark-ground illumina- 
tion and then watching the crystallization. 
REFRACTION AND COLOR IMAGES. 
| 61. Refraction Images are those mostly seen in studying microscopic objects. 
They are the appearances due to the refraction of the light in passing from the 
mounting medium into the object and from the object back into the mounting 
medium. With such images the diaphragms should not be too large (see § 45). 
If the color and refractive index of the object were exactly like the mount- 
ing medium it could not be seen. In most cases both refractive index and color 
differ somewhat, there is then a combination of color and refraction images which 
is a great advantage. This method of illumination is mostly used in histology. 
£ 62. Color Images.—These are images of objects which are strongly colored 
and lighted with so wide an aperture that the refraction images are drowned in 
the light. Such images are obtained by removing the diaphragm or by using a 
larger opening. This method of illumination is specially applicable to the study 
of stained microbes. (See below \ 67). 
ADJUSTABLE, WATER AND HOMOGENEOUS OBJECTIVES. 
EXPERIMENTS. 
§ 63. Adjustment for Objectives.—As stated above (§ 16), the ab- 
erration produced by the cover-glass (PI. V., Fig. 41), is compensated 
for by giving the combinations in the objective a different relative posi- 
tion than they would have if the objective were to be used on uncovered 
objects. Although this relative position cannot be changed in uuad- 
justable objectives, one can secure the best results of which the object- 
ive is capable by selecting the thickness for which the object- 
ive was corrected. (See table in § 17). Adjustment may be made 
also by increasing the tube-length (§ 17) for covers thinner than the stand- 
ard, and by shortening the tube-length for covers thicker than the 
standard (§ 17). 
Adjustable Objectives.—The proper adjustment of objectives, that is, 
the adjustment which gives the truest image, requires both insight and 
experience ; for the structure of an object does not appear the same 
with different adjustments of the objective. And as the opinion of 
different observers on the structure of objects varies, they adjust the 
objectives differently, and try to obtain the adjustment which will show 
a structure in accordance with their opinion. Eyes also differ, and two 
observers might find it necessary to adjust the same objective differently 
to produce an identical appearance for each of them. 23 
MICROSCOPE AND ACCESSORIES. 
In learning to adjust objectives, it is best for the student to choose 
some object whose structure is well agreed upon, and then to practice 
lighting it, shading the stage and adjusting the objective, until the 
proper appearance is obtained. The adjustment is made by turning a 
ring or collar which acts on a screw and increases or diminishes the dis- 
tance between the systems of lenses, usually the front and the back 
systems (Fig. 13). In adjustable objectives the back systems should be 
movable, the front one remaining fixed so that there will be no danger 
of bringing the objective down upon the object. If the front system is 
movable, the body of the microscope should be raised slightly every 
time the adjustment is altered. 
General Directions.—(A) The thinner the cover-glass the further 
must the systems of lenses be separated, i. e., the adjusting collar is 
turned nearer the zero or the mark “uncovered,” and conversely, (B) 
the thicker the cover-glass, the closer together are the systems brought 
by turning the adjusting collar from the zero mark. This also increases 
the magnification of the objective (Cli. III). 
The following specific directions for making the cover-glass adjust- 
ment are given by Mr. Wenham [(C. 166)] : “ Select any dark speck or 
opaque portion of the object, and bring the outline into perfect focus ; 
then lay the finger on the milled-head of the fine motion, and move it 
briskly backwards and forwards in both directions from the first posi- 
tion. Observe the expansion of the dark outline of the object, both 
when within and when without the focus. If the greater expansion or 
coma, is when the object is without the focus, or farthest from the ob- 
jective [z. e., in focusing up], the lenses must be placed further asunder, 
or toward the mark uncovered [z. e., the adjusting collar is turned toward 
the zero mark as the cover-glass is too thin for the present adjustment]. 
If the greater expansion is when the object is within the focus, or near- 
est the objective, [i. e., in focusing down], the lenses must be brought 
closer together or toward the mark covered [i. <?., the adjusting collar 
should be turned away from the zero mark, the cover-glass being too 
thick for the present adjustment].” In most objectives the collar is grad- 
uated arbitrarily, the zero (O) mark representing the position for uncov- 
ered objects. Other objectives have the collar graduated to correspond to 
the various thickness of cover-glasses for which the objective may be ad- 
justed. This seems to be an admirable plan; then if one knows the 
thickness of the cover-glass on the preparation (C/z. V) the adjusting col- 
lar may be set at a corresponding mark, and one will feel confident that 
the adjustment will be approximately eorrect. It is then only necessary 
for the observer to make the slight adjustment to compensate for the mount- 
ing medium or any variatio7i from the standard length of the tube of the 
microscope. In adjusting for variations of the length of the tube from 24 
MICROSCOPE AND ACCESSORIES. 
the standard it should be remembered that: (A) If the tube of the mi- 
croscope is longer than the standard for which the objective was cor- 
rected, the effect is approximately the same as thickening the cover- 
glass, and therefore the systems of the objective must be brought closer 
together, i. <?., the adjusting collar must be turned away from the zero 
mark. (B) If the tube is shorter than the standard for which the ob- 
jective is corrected, the effect is approximately the same as diminishing 
the thickness of the cover-glass, and the systems must therefore be sep- 
arated, that is, the adjusting collar turned toward the zero mark (Fig. 
57)- 
Furthermore, whatever the interpretation by different opticians of 
what should be included in “tube-length,” and the exact length in 
millimeters, its importance is very great; for each objective gives the 
most perfect image of which it is capable with the “tube-length” for 
which it is corrected, and the more perfect the objective the greater the 
ill effects on the image of varying the “ tube-length ” from this stand- 
ard. The plan of designating exactly what is meant by ‘ ‘ tube-length, ’ ’ 
and engraving on each objective the “ tube-length ” for which it is cor- 
rected, is to be commended, for it is manifestly difficult for each worker 
with the microscope to find out for himself for what “tube-length” 
each of his objectives was corrected. 
§64. Water Immersion Objectives.—Put a water immersion ob- 
jective in position (§ 30) and the fly’s wing for object under the micro- 
scope. Place a drop of distilled water on the cover-glass and with the 
coarse adjustment lower the tube till the objective dips into the water, 
then light the field well and turn the fine adjustment one way and the 
other till the image is clear. Water immersions are exceedingly con- 
venient in studying the circulation of the blood and for many other 
purposes where aqueous liquids are liable to get on the cover-glass. 
If the objective is adjustable, follow the directions given in § 63. 
When one is through using a water immersion objective, remove it 
from the microscope and with some Japanese bibulous paper (§ 72) 
wipe all the water from the front-lens. Unless this is done dust col- 
lects and sooner or later the front-lens would be clouded. It is better to 
use distilled water to avoid the gritty substances that are liable to be 
present in natural waters, as these gritty particles might scratch the 
front-lens. 
HOMOGENEOUS IMMERSION OBJECTIVES : EXPERIMENTS. 
§ 65. As stated above, these are objectives in which a liquid of the 
same refractive index as the front-lens of the objective is placed be- 
tween the front-lens and the cover glass. 25 
MICROSCOPE AND ACCESSORIES. 
Put a 2 mm. (TVth. in.) homogeneous immersion objective in posi- 
tion, employ an Abbe illuminator. 
§ 66. Refraction Images.—Use some histological specimen like a 
muscular fiber as object, make the diaphragm opening only slightly 
larger than the front-lens, add a drop of the homogeneous immersion 
liquid and focus as directed in §§ 64 and 67. The object wall be 
clearly seen in all its details by the unequal refraction of the light 
traversing it. The difference in color between it and the surrounding 
medium will also increase the sharpness of the outline. If an air bub- 
ble preparation (§ 52) were used, one would get pure, refraction 
images. 
§ 67. For Color Images.—Use some stained microbes, as Bacillus 
tuberculosis for object. Put a drop of the immersion liquid 011 the cov- 
er-glass or the front-lens of the homogeneous objective. Remove 
the diaphragms from the illuminator or use a very large opening. 
Focus the objective down so that the immersion fluid is in contact with 
both the front-lens and the cover-glass, then with the fine adjustment 
get the microbes in focus. They will stand out as colored rods on a 
bright field. 
§ 68. Shading the Objecft—To get the clearest image of an object 
no light should reach the eye except from the object. A handkerchief 
or a dark cloth wound around the objective will serve the purpose. 
Often the proper effect may be obtained by simply shading the top of 
the stage with the hand or with a piece of bristol board. Unless one 
has a very favorable light the shading of the object is of the greatest 
advantage, especially with homogeneous immersion objectives. 
§ 69. Cleaning Homogeneous Objectives.—After one is through 
with a homogeneous objective, it should be carefully cleaned as follows : 
Wipe off the homogeneous liquid with a piece of the Japanese paper 
(§ 72), then if the fluid is cedar oil, wet one corner of a fresh piece in 
benzin and wipe the front-lens with it. Immediately afterward wipe 
with a dry part of the paper. The cover-glass of the preparation can 
be cleaned in the same way. If the homogeneous liquid is a glycerin 
mixture proceed as above, but use water instead of benzin to remove 
the last traces of glycerin. 
CARE OF THE MICROSCOPE. 
§ 70. The microscope should be handled carefully, and kept perfectly 
clean. The oculars and objectives should never be allowed to fall. 
When not in use keep it in a place as free as possible from dust. 
All parts of the microscope should be kept free from liquids, especially 
from acids, alkalies, alcohol, benzin, turpentine and chloroform. 
§ 71. Care of the Mechanical Parts.—To clean the mechanical 26 
MICROSCOPE AND ACCESSORIES. 
parts put a small quantity of some fine oil, (olive oil and benzin equal 
parts), on a piece of chamois leather or on the Japanese paper, and rub 
the parts well, then with a clean dry piece of the chamois or paper wipe 
off the oil. If the mechanical parts are kept clean in this way a lubri- 
cator is rarely needed. Where opposed brass surfaces cut, a very slight 
application of equal parts of beeswax and tallowT well melted together 
serves a good purpose. 
In cleaning lacquered parts, benzin alone answers well, but it should 
be quickly wiped off with a clean piece of the Japanese paper. Do not 
use alcohol as it dissolves the lacquer. 
§ 72. Care of the Optical Parts.—These must be kept scrupulously 
clean in order that the best results may be obtained. 
Glass surfaces should never be touched with the fingers, for that will 
soil them. 
The glass of which the lenses are made is quite soft, consequently it 
is necessary that only soft, clean cloths or paper be used in wiping them. 
‘ ‘ Paper for Cleaning the Lenses of Objectives and Oculars.—For the 
last six years the so-called Japanese filter paper (the bibulous paper 
often used by dentists when filling teeth), has been used in the labora- 
tory for cleaning the lenses of oculars and objectives, and especially for 
removing the fluid used with immersion objectives. Whenever a piece 
is used once it is thrown away. It has proved more satisfactory than 
cloth or chamois, because dust and sand are not present; and from its 
bibulous character it is very efficient in removing liquid or semi-liquid 
substances. ’ ’ 
Dust may be removed with a camel’s hair brush, or by wiping with 
the soft paper. 
Cloudiness may be removed from the glass surfaces by breathing on 
them, then wiping quickly with a soft cloth or the bibulous paper. 
Cloudiness on the inner surfaces of the ocular lenses may be removed 
by unscrewing them and wiping as directed above. A high objective 
should never be taken apart by an inexperienced person. 
If the cloudiness cannot be removed as directed above, moisten one cor- 
ner of the cloth or paper with 95 per cent, alcohol, wipe the glass first 
with this, then with the dry cloth or the paper. 
Water may be removed with soft cloth or the paper. 
Glycerin may be removed with cloth or paper saturated with distilled 
water ; remove the water as above. 
Blood or other albuminous material may be removed while fresh with 
a moist cloth or paper, the same as glycerin. If the material has dried 
to the glass, it may be removed more readily by adding a small quan- 
tity of ammonia to the water in which the cloth is moistened, (water 
100 cc., ammonia 1 cc). 27 
MICROSCOPE AND ACCESSORIES. 
Canada Balsam, damar, paraffin, or any oily substance, may be re- 
moved with a cloth or paper wet with chloroform, turpentine or benzin. 
The application of these liquids and their removal with a soft, dry cloth 
or paper should be as rapid as possible, so that none of the liquid will 
have time to soften the setting of the lenses. 
Shellac Cement may be removed by the paper or a cloth moistened in 
95 per cent, alcohol. 
Brunswick Black, Gold Size, and all other substances soluble in chlo- 
roform, etc., may be removed as directed for balsam and damar. 
In general, use a solvent of the substance on the glass and wipe it off 
quickly with a fresh piece of the Japanese paper. 
It frequently happens that the upper surface of the back combination 
of the objective becomes dusty. This may be removed in part by a 
brush, but more satisfactorily by using a piece of the soft paper loosely 
twisted. When most of the dust is removed some of the paper may be 
put over the end of a pine stick (like a match stick) and the glass sur- 
face carefully wiped. 
CARE OF THE EYES. 
§ 73- Keep both eyes open, using the eye-screen if necessary (Fig. 
18, and PI. II, Fig. 16) ; and divide the labor between the two eyes, i. 
e., use one eye for observing the image awhile and then the other. In 
the beginning it is not advisable to look into the microscope continu- 
ously for more than half an hour at 
a time. One never should work w7ith 
the microscope after the eyes feel fa- 
tigued. After one becomes accus- 
tomed to microscopic observation he 
can work for several hours with the 
microscope without fatiguing the eyes. This is due to the fact that 
the eyes become inured to labor like the other organs of the body by 
judicious exercise. It is also due to the fact that but very slight accom- 
modation is required of the eyes, the eyes remaining nearly in a condi- 
tion of rest as for distant objects. The fatigue incident upon using the 
microscope at first is due partly at least to the constant effort to accom- 
modate the eye for a near object. With a microscope of the best quali- 
ty, and suitable light—that is light which is steady and not so bright as 
to dazzle the eyes nor so dim as to strain them in determining details— 
microscopic work should improve rather than injure the sight. 
Fig. 18.— Ward’s Eye-Shade. 
A LABORATORY COMPOUND MICROSCOPE. 
§ 74- For the purpose of modern histological investigation and of advanced mi- 
croscopical work in general, a microscope should have something like the follow- 
ing character : Its optical outfit should comprise, (a) dry objectives of 50 mm. (2 28 
MICROSCOPE AND ACCESSORIES. 
in.), 16-18 mm. in.) and 3 mm. (in.) equivalent focus. There should be present 
also a 2 mm. in.) or 1,5 mm. (x\ in.) homogeneous immersion objective. Of 
oculars there should be several of different power. An Abbe illuminator, and an 
Abbe camera lucida are also necessities. A micro-spectroscope and a micro-polar- 
izer are very desirable. 
Even in case all the optical parts cannot be obtained in the beginning, it is wise 
to secure a stand upon which all may be used when they are finally secured. 
Mechanical Parts or Stand.—The stand should be low enough so that it can be 
used in a vertical position on an ordinary table without inconvenience ; it should 
have a jointed (flexible) pillar for inclination at any angle to the horizontal. The 
adjustments for focusing should be two,—a coarse adjustment or rapid movement 
with rack and pinion, and a fine adjustment by means of a micrometer screw. 
Both adjustments should move the entire body of the microscope. The body or 
tube should be short enough for objectives corrected for the short or 160 millime- 
ter tube-length, and the draw-tube should be graduated in centimeters and milli- 
meters. The lower end of the draw-tube and of the tube should each possess a 
standard screw for objectives (PI. II, Fig. 10). The stage should be quite large 
for the examination of slides with serial sections ; it is also of considerable advan- 
tage to have the stage with a circular, revolving top, and two centering screws 
with milled heads. In this way a mechanical stage with limited motion is se- 
cured, and this is of the highest advantage in using powerful objectives. The 
sub-stage fittings should be so arranged as to enable one to dispense entirely with 
diaphragms, to use ordinary diaphragms, or to use the Abbe illuminator. The il- 
luminator mounting should allow up and down motion, preferably by rack and 
pinion. The base should be sufficiently heavy and so arranged that the micros- 
cope will be steady in all positions, and interfere the least possible amount with 
the manipulation of the mirror and other sub-stage accessories. 
A microscope with all the accessories mentioned above would cost about $ 170 
in Europe. Without the micro-spectroscope and micro-polarizer about $115. 
To get the American price of a foreign instrument or the catalogue price of one 
of American manufacture, the amount of duty (i. e., 60 per cent.) should be added. 
REFERENCES FOR CHAPTER I. 
In the appendix will be given a bibliography, with full titles, of the woiks 
and periodicals referred to. In the text the works are mostly designated by single 
letters, and the periodicals by the initial letters of their titles. 
The works of Beale (B.), Bausch (Bau.), Behrens (Beh.), Carpenter (C.), Dippel 
(D.), Frey (F.), Hogg (H.), Mayall, Nageli mid Schweudeuer, Robin. 
The following special articles in periodicals may be examined with advantage : 
\ 14. Apochromatic Objectives, etc. Dippel in Zeit. wiss. Mikr. 1886, p. 303 ; 
also in the Jour. Roy. Micr. Soc., 1886, pp. 316, 849, 1110 ; same, 1890, p. 480 ; Zeit. 
f. Iustrumentenk., 1890, pp. 1-6; Micr. Built., 1891, pp. 6-7. 
\ 17. Tube-length, etc. Gage, Proc. Amer. Soc. Micrs., 1887, pp. 168-172; also 
in the Microscope, the Jour. Roy. Micr. Soc., and in Zeit. wiss. Mikr., 1887-8, 
Bausch, Proc. Amer. Soc. Micrs., 1890, pp. 43-49 ; also in the Microscope, 1890, 
pp. 289-296. 
$ 18. Aperture. J. D. Cox, Presidential Address, Proc. Amer. Soc. Micrs., 1884, 
PP- 5-39. Jour. R°y- Micr. Soc., 1881, pp. 303, 348, 365, 388 ; 1882, pp. 300, 460; 
1883, p. 790; 1884, p. 20. 
\ 54. The Abbe Illuminator. Arcliiv f. mikr. Anat., Vol. IX, (1873) P- 469- CHAPTER II. 
INTERPRETATION OF APPEARANCES. 
APPARATUS AND MATERIAE FOR CHAPTER II. 
A laboratory, compound microscope (§ 74) ; Preparation of fly’s wing (see ap- 
pendix) ; 50 per cent, glycerin ; Slides and covers ; Preparation of letters in 
stairs (Fig. 23 in PI. Ill) ; Mucilage for air-bubbles and olive or clove oil for oil- 
globules ($ 81) ; Solid glass rod, and glass tube (§ 89) ; Collodion (§ 91) ; Carmine, 
India ink, or lamp black ($ 93) ; Frog, and castor oil or paraffin, micro-polari- 
scope (2 95). 
INTERPRETATION OF APPEARANCES UNDER THE MICROSCOPE 
§ 75- General Remarks.—The experiments in this chapter are 
given secondarily for drill in manipulation, but primarily so that the 
student may not be led into error or puzzled by appearances which are 
constantly met with in microscopical investigation. Any one can look 
into a microscope, but it is quite another matter to interpret correctly 
the meaning of the appearances seen. 
It is especially important to remember that the more of the relations 
of any object are known, the truer is the comprehension of the object. 
In microscopical investigation every object should be scrutinized from 
all sides and under all conditions in which it is likely to occur in nature 
and in microscopical investigation. It is best also to begin with ob- 
jects of considerable size whose character is well known, to look at 
them carefully with the unaided eye so as to see them as wholes and 
in their natural setting. Then a low power is used, and so on step 
by step until the highest power available has been employed. One 
will in this way see less and less of the object as a whole, but every in- 
crease in magnification will give increased prominence to detail, detail 
which might be meaningless when taken alone and independent of the 
object as a whole. The pertinence of this advice will be appreciated 
when the student undertakes to solve the problems of histology ; for 
even after all the years of incessant labor spent in trying to make out 
the structure of man and the lower animals, many details are still in 
doubt, the same visual appearances being quite differently interpreted 
by eminent observers- 
§ 76. Dust or Cloudiness on the Ocular.—Employ the 18 mm. 
(% in.) objective, low ocular, and fly’s wing, as object. 
Unscrew the field-lens and put some particles of lint or dark cloth on 
its upper surface. Replace the field-lens and put the ocular in position EXPLANATION OF PLATE III. 
Fig. 20, 20a, 21 and 22. Sectional views of the Abbe Illuminator of 1.20 N. A. 
18, 54), showing various methods of illumination (Ci 54-59). Fig. 20, axial 
light with parallel rays. Fig. 20a, oblique light. Fig. 21, axial light with con- 
verging beam. Fig. 22, dark-ground illumination with a central stop diaphragm. 
Axis. The optic axis of the illuminator and of the microscope. The illumina" 
tor is centered, that is its optic axis is a prolongation of the optic axis of the mi- 
croscope. 
S. Axis. Secondary axis. In oblique light the central ray passes along a sec- 
ondary axis of the illuminator, and is therefore oblique to the principal axis. 
A. Fig. 21 represents the upper part of the illuminator. 
D D. Diaphragms. These are placed in sectional and in face views. The dia- 
phragm is placed between the mirror and the illuminator. In Fig. 20 the opening 
is excentric for oblique light, and in Fig. 22 the opening is a narrow band, the cen- 
tral part being stopped out, and thus giving rise to dark-ground illumination 
(i 60). 
Obj. Obj. The front of the objective. 
Fig. 23. Showing the method of mounting letters in stairs to show the order of 
coming into focus. 
a, b, c, d. The various letters indicated by the oblique row of black marks in the 
sectional view. 
Slide. The glass slide on which the letters are mounted. 
Fig. 24. Glass rod showing the appearance in air (a), and in 50 per cent, glycerin 
(b), a 80). 
Fig. 25. Glass rod coated with collodion to show Double Contour. At the left 
the collodion is represented as collecting in a drop (i 91). 
Fig. 26. Mammalian blood-corpuscles on edge to show a surface view (a), and an 
optical section (b). 
Fig. 27. Wollaston's Camera Lucida, showing the rays from the microscope and 
from the drawing surface, and the position of the pupil of the eye. 
Axis, Axis. Axial rays from the microscope and from the drawing surface. 
(| 121). 
Camera Lucida. A section of the quadrangular prism showing the course of the 
rays in the prism from the microscope to the eye. As the rays are twice reflected, 
the}' have the same relation on entering the ey e that they would have by looking 
directly into the ocular. 
A B. The lateral rays from the microscope and their projection on the drawing 
surface. 
C D. Rays from the drawing surface to the eye. 
A D, A/ DA Overlapping portion of the two fields, where both the microscopic 
image and the drawing surface, pencil, etc., may both be seen. It is represented 
by the shaded part in the overlapping circles at the right. 
Ocular. The ocular of the microscope. 
P. The drawing pencil. Its point is shown in the overlapping fields. 
Fig. 28. Figure showing the position of the microscope, the camera lucida, and 
the eve, and the different sizes of the image depending upon the distance at which 
it is projected from the eye. (a) The size at 25 cm. ; (b) at 35 cm. (§ 104). 
Fig. 29. Figure showing the appearance of the lines of the stage micrometer 
(the coarse lines) and of the ocular micrometer when using a high objective ($ 117). 
A. One method of measuring the spaces by putting the ocular micrometer line 
opposite the center of the stage micrometer line. 
B. Method of measuring the space of the stage micrometer by putting one line 
of the ocular micrometer at the inside and one at the outside of the lines of the 
stage micrometer ($ 117). 30 
INTERPRETATION OF APPEARANCES. 
(§ 3i)> Light the field well and focus sharply. The image will be 
clear, but part of the field will be obscured by the irregular outline of 
the particles of lint. Move the object to make sure this appearance is 
not due to it. 
Grasp the ocular by the milled ring, just above the tube of the mi- 
croscope, and rotate it. The irregular object will rotate with the ocu- 
lar. Cloudiness or particles of dust on any part of the ocular, may be 
detected in this way. 
§ 77. Dust or Cloudiness on the Objective.—Employ the same 
ocular and objective as before (§ 76), and the fly’s wing as object. 
Focus and light well, and observe carefully the appearance. Rub gly- 
cerin on one side of a slide near the end. Hold the clean side of this 
end close against the objective. The image will be obscured, and can 
not be made clear by focusing. Then use a clean slide, and the image 
may be made clear by elevating the body slightly. The obscurity pro- 
duced in this way is like that caused by clouding the front-lens of the 
objective. Dust would make a dark patch on the image that would 
remain stationary while the object or ocular was moved. 
If too small a diaphragm is employed, only the central part of the 
field will be illuminated, and around the small light circle will be seen 
a dark ring. 
§ 78. Relative Position of Objects or parts of the same object.— 
The general rule is that objects highest up come into focus last in focus- 
ing up, first in focusing down. 
§ 79. Objects Having Plane or Irregular Outlines.—As object 
use three printed letters mounted in stairs in Canada balsam (PI. Ill, 
Fig. 23, Ch. V). The first letter is placed directly upon the slide, and 
covered with a small piece of glass about as thick as a slide. The 
second letter is placed upon this and covered in like manner. The 
third letter is placed upon the second thick cover and covered with an 
ordinary cover-glass. The letters should be as near together as possi- 
ble, but not overlapping. Employ the same ocular and objective as 
above (§ 76). 
Lower the tube till the objective almost touches the top letter, then 
look into the microscope, and slowly focus up. The lowest letter will 
first appear, and then, as it disappears, the middle one will appear, 
and so on. Focus down, and the top letter will first appear, then the 
middle one, etc. The relative position of objects is determined exactly 
in this way in practical work. 
§ 80. Transparent Objects Having Curved Outlines.—The suc- 
cess of these experiments will depend entirely upon the care and skill 
used in preparing the objects, in lighting, and in focusing. 
Employ a 5 mm. in.) or higher objective and a high ocular for all 31 
INTERPRETATION OF APPEARANCES. 
the experiments. It may be necessary to shade the object (§ 66) to get 
satisfactory results. When a diaphragm is used the opening should be 
small (§ 44). 
§ 81. Air Bubbles.—Prepare these by placing a drop of thin mucilage 
on the center of a slide and beating it with a scalpel blade until the muci- 
lage looks milky from the inclusion of air bubbles. Put on a cover- 
glass (Ch. V), but do not press it down. 
§ 82. Air Bubbles with Central Illumination.—Shade the object; 
and with the plane mirror, light the field with central light (PI. II, Fig. 
13, §42). 
Search the preparation until an air bubble is found appearing about 
1 mm. in diameter, get it into the center of the field and if the light is 
central the air bubble will appear with a wide, dark, circular margin 
and a small bright center. If the bright spot is not in the center, ad' 
just the mirror until it is. 
This is one of the simplest and surest methods of telling when the 
light is central or axial (§ 52). 
Focus both up and down, noting that in focusing up the central spot 
becomes very clear and the black ring very sharp. On elevating the 
body still more the center becomes dim, and the whole bubble loses its 
sharpness of outline. 
§ 83. Air Bubbles with Oblique Illumination.—Remove the sub- 
stage of the microscope (Fig. 10), and all the diaphragms. Swing the 
mirror so that the rays may be sent very obliquely upon the object (Fig. 
13, C). The bright spot will appear no longer in the center but on the 
side away from the mirror (Fig. 19). 
§ 84. Oil Globules.—Prepare these by beating a small drop of clove 
oil with mucilage on a slide and covering as directed for air bubbles (§ 
81). 
§ 85. Oil Globules with Central Illumination.—Use the same dia- 
phragm and light as above (§ 82). Find an oil globule appearing about 
1 mm. in diameter. If the light is central the bright spot will appear 
in the center as with air (§ 82). Focus up and down as with air ; and 
note that the bright center of the oil globule is clearest last in focusing 
up. 
§ 86. Oil Globules with Oblique Illumination.—Remove the sub- 
stage, etc., as above, and swing the mirror to one side and light with 
oblique light. The bright spot will be eccentric, and will appear to be 
011 the same side as the mirror (Fig. 19). 
§ 87. Oil and Air Together.—Make a preparation exactly as de- 
scribed for air bubbles (§ 81), and add at one edge a little of the mix- 
ture of oil and mucilage (§ 84) ; cover and examine. 32 
INTERPRETATION OF APPEARANCES. 
The sub-stage need not be used in this experiment. Search the 
preparation until an air bubble and an oil globule, each about i mm. 
in diameter, are found in the same field of view. Tight first with cen- 
tral light, and note that in focusing up the air 
bubble comes into focus first and that the central 
spot is smaller than that of the oil globule. 
Then, of course, the black ring will be wider in 
the air bubble than in the oil globule. Make 
the light oblique. The bright spot in the air 
bubble will move away from the mirror while 
that in the oil globule will move toward it. See 
Fig. 19.* 
§ 88. Air and Oil by Reflected Light.—Cov- 
er the diaphragm or mirror so that no transmitted 
light (§41) can reach the preparation, using the 
same preparation as in (§ 87). The oil and air 
will appear like globes of silver on a dark 
ground. The part that was darkest in each will 
be lightest, and the bright central spot will be somewhat dark.f 
§ 89. Distinctness of Outline.—In refraction images (§§ 61, 66) 
this depends on the difference between the refractive power of a body 
and that of the medium which surrounds it. The oil and air were very 
distinct in outline as each differed greatly in refractive power from the 
medium which surrounded them, the oil being more refractive than the 
mucilage and the air less. 
Place a fragment of a cover-glass on a clean slide, and cover it (see 
Ch. V, under mounting). The outline will be very distinct with the 
unaided eye. Use it as object and employ the 18 mm. (ff in.) objective 
and high ocular. Light with central light. The fragment will be out- 
lined by a dark band. Put a drop of water at the edge of the cover- 
glass. It will run in and immerse the fragment. The outline will re- 
main distinct, but the dark band will be somewhat narrower. Re- 
move the cover-glass, wipe it dry, and wipe the fragment and slide dry 
also. Put a drop of 50% glycerin on the middle of the slide and mount 
Fig. 19.— Very Small Globule of 
Oil (O) and an Air-Bubble 
(A) Seen by Oblique Light. 
The Arrow Indicates the Di- 
rection of the Light Rays . 
*It should be remembered that the image in the compound microscope is in- 
verted (Fig. 5), hence the bright spot really moves toward the mirror for air, and 
away from it for oil. 
t It is possible to distinguish oil and air optically, as described above, only 
when quite high powers are used and very small bubbles are selected for observa- 
tion. If an 18 mm. in.) is used instead of a 3 mm. in.) objective, the ap- 
pearances will vary considerably from that given above for the higher power. It 
is well to use a low as well as a high power. Marked differences will also be seen 
in the appearances with objectives of small and of large aperture. 33 
INTERPRETATION OF APPEARANCES. 
the fragment of cover-glass in that. The dark contour will be much 
narrower than before. 
Draw a solid glass rod out to a fine thread. Mount one piece in air, 
and the other in 50% glycerin. Put a cover-glass on each. Employ 
the same optical arrangement as before. Examine the one in air first. 
There will be seen a narrow, bright band, with a wide dark band on 
each side. 
The one in glycerin will show a much wider bright central band, 
with the dark borders correspondingly narrow (PI. Ill, Fig. 24). 
If the glass rod or any other object were mounted in a medium of 
the same color and refractive power, it could not be distinguished from 
the medium.* 
§ 90. Highly Refractive.—This expression is often used in describ- 
ing microscopic objects, (medulated nerve fibres for example), and 
means that the object will appear to be bordered by a wide, dark 
margin when it is viewed by transmitted light. And from the above 
(§ 89), it would be known that the refractive power of the object, and 
the medium in which it was mounted must differ considerably. 
§ 91. Doubly Contoured.—This means that the object is bounded 
by two, usually parallel dark lines with a lighter band between them. 
In other words the object is bordered by (1) a dark line, (2) a light 
band, and (3) a second dark line (PI. Ill, Fig. 25). 
This may be demonstrated by coating a fine glass rod (§ 89) with 
one or more coats of collodion or celloidin and allowing it to drj% and 
then mounting in 50% glycerin as above (§ 89). Employ a 5 111m. 
(T in.) or higher objective, light with transmitted light, and it will be 
seen that where the glycerin touches the collodion coating there is a 
dark line—next this is a light band, and finally there is a second dark 
line where the collodion is in contact with the glass rodf (PI. Ill, 
Fig- 25). 
§ 92. Optical Section.—The appearance obtained in examining 
transparent or nearly transparent objects with a microscope when some 
plane below the upper surface of the object is in focus. The upper 
part of the object which is out of focus obscures the image but slightly. 
By changing the position of the objective or object, a different plane 
* Some of the rods have air bubbles in them, and then there results a capillary 
tube when they are drawn out. It is well to draw out a glass tube into a fine 
thread and examine it as described. The central cavity makes the experiment 
much more complex. 
t The collodion used is a 5 per cent, solution of gun cotton in equal parts of 
sulphuric ether and 95 per cent, alcohol. It is well to dip the rod two or three 
times in the collodion and to hold it vertically while drying. The collodion will 
gather in drops and one will see the difference between a thick and a thin mem- 
branous covering (Fig. 25). 34 
INTERPRETATION OF APPEARANCES. 
will be in focus and a different optical section obtained. The most 
satisfactory optical sections are obtained with high objectives having 
large aperture (§ 18). 
Nearly all the transparent objects studied may be viewed in optical 
section. A striking example will be found in studying mammalian red 
blood-corpuscles on edge. The experiments with the solid glass rods 
(§§ 89, 91) furnish excellent and striking examples of optical sections 
(PI. Ill, Fig. 24-26). 
§ 93. Currents in Liquids.—Employ the 18 mm. in.) objective, 
and as object put a few particles of carmine on the middle of a slide, 
and add a drop of water. Grind the carmine well with a scalpel blade, 
and then cover it. If the microscope is inclined, a current will be pro- 
duced in the water, and the particles of carmine will be carried along 
by it. Note that the particles seem to flow up instead of dowm, why 
is this (§§ 3, 34) ? 
Lamp-black rubbed in water containing a little mucilage answers 
well for this experiment. 
§ 94. Pedesis or Brownian Movement.—Employ the same object 
as above, but a 5 mm. (A in.) or higher objective in place of the 18 mm. 
Make the body of the microscope vertical, so that there may be no cur- 
rents produced. Use a small diaphragm and light the field well. 
Focus, and there will be seen in the field large motionless masses, and 
between them small masses in constant motion. This is an indefinite 
dancing or oscillating motion. 
This indefinite but continuous motion of small particles in a liquid 
is called Pedesis or Brownian movement. Also, but improperly, molecular 
movement, from the smallness of the particles. 
The motion is increased by adding a little gum arabic solution or a 
slight amount of silicate of soda or of soap ; sulphuric acid and various 
saline compounds retard or check the motion. One of the best objects 
is pumice stone ground finely. I11 this the movement is so active that 
it is difficult to follow the course of single particles. Pedesis is exhibited 
by all solid matter if finely enough divided and in a suitable liquid. 
No adequate explanation of this phenomenon has yet been offered. 
See Carpenter 182-183, Beale 195, Jevons in Quart. Jour. Science, new 
series, Vol. VIII, (1878), p. 167. 
Compare the pedetic motion with that of a current by slightly inclin- 
ing the body of the microscope. The small particles will continue their 
independent leaping movements while they are carried along by the 
current. 
§ 95. Demonstration of Pedesis with the Polarizing Micro- 
scope.—The following demonstration shows conclusively that the pe- 
detic motion is real and not illusive. (Ranvier, p. 173). 35 
INTERPRETATION OF APPEARANCES. 
Open the abdomen of a dead frog (an alcoholic specimen will do) ; 
turn the viscera to one side and observe the small whitish masses at the 
emergence of the spinal nerves. With fine forceps remove one of these 
and place it on the middle of a clean slide. Add a drop of water, or of 
water containing a little gum arabic. Rub the white mass around in 
the drop of liquid and soon the liquid will have a milky appearance. 
Remove the white mass, place a cover-glass on the milky liquid and 
seal the cover by painting a ring of castor oil all around it, half the 
ring being on the slide and half on the cover-glass. This is to avoid 
the production of currents by evaporation. 
Put the preparation under the miroscope and examine with first a low 
then a higher power (3 mm. or in.). In the field will be seen mul- 
titudes' of crystals of carbonate of lime, the larger crystals are motion- 
less but the smallest ones exhibit marked pedetic movement. 
Use the micro-polariscope (see Ch. IV), light with great care and ex- 
clude all adventitious light from the microscope by shading the object 
(§ 66) and also by shading the eye. Focus sharply and observe the 
pedetic motion of the small particles, then cross the polarizer and anal- 
yzer, that is, turn one or the other until the field is dark. Part of the 
large motionless crystals will shine continuously and a part will remain 
dark, but the small crystals between the large ones will shine for an 
instant, then disappear, only to appear again the next instant. This 
demonstration is believed to furnish absolute proof that the pedetic 
movement is real and not illusory. 
§ 96. In addition to the above experiments it is very strongly recom- 
mended that the student follow the advice of Beale, p. 248, and exam- 
ine first with a low then a higher power mounted dry, then in water, 
lighted with reflected light, then with transmitted light, the following : 
Potato, wheat, rice, and corn starch, easily obtained by scraping the 
potato and the grains mentioned ; bread crumbs ; portions of feather. 
Portions of feather accidentally present in histological preparations 
have been mistaken for lymphatic vessels (B. 248). Fibers of cotton, 
linen and silk. Textile fibers accidentally present have been consid- 
ered nerve fibers, etc. Human and animal hairs, especially cat hairs. 
These are very liable to be present in preparations made in this labora- 
tory. The scales of butterflies and moths, especially the common 
clothes moth. The dust swept from carpeted and wood floors. Tea 
leaves and coffee grounds. Dust found in living rooms in places not 
frequently dusted. In the last will be found a regular museum of ob- 
jects. 
For different appearances due to the illuminator see Nelson, in Jour. 
Roy. Micr. Soc., 1891, pp. 90-105. CHAPTER III. 
MAGNIFICATION, MICROMETRY AND DRAWING. 
APPARATUS AND MATERIAL FOR THIS CHAPTER. 
Simple and compound microscope (Ch. I) ; Steel scale or rule divided to milli- 
meters and |ths ; Block for magnifier and compound microscope ($ 98, 102); Divi- 
ders (§ 98, 99, 102); Stage micrometer (§ 101) ; Wollaston’s camera lucida (§ 102, 
121); Ocular micrometer (§ 112); Micrometer ocular ($ 114). Abbe camera lucida 
(U 122-127). 
§ 97. The Magnification, Amplification or Magnifying Power 
of a microscope or any of its parts is the number obtained by dividing 
any linear dimension of the image by the corresponding linear dimen- 
sion of the object magnified. For example, if the image of some ob- 
ject is 40 mm. long, and the actual length of the object magnified is 
2 mm. the magnification is 40-7-2=20. 
Magnification is expressed in diameters or times linear, that is but 
one dimension is considered. In giving the scale at which a microsco- 
pical or histological drawing is made, the word magnification is fre- 
quently indicated by the sign of multiplication thus : X 450, upon a 
drawing would mean that the figure or drawing is 450 times as large as 
the object. 
MAGNIFICATION OF A SIMPLE MICROSCOPE. 
§ 98. The Magnification of a Simple Microscope is the ratio 
between the object magnified (Fig. 4, A B), and the virtual image (Fig. 
4, A'iB'). To obtain the size of the image (Fig. 4, A' B'), place the 
tripod magnifier near the edge of a support of such a height that the 
distance from the upper surface of the magnifier to the table is 250 
millimeters. 
As object, place a scale of some kind ruled in millimeters on the sup- 
port under the magnifier. Put some white paper on the table at the 
base of the support, and on the side facing the light. 
Close one eye, and hold the head so that the other will be near the 
upper surface of the lens. Focus if necessary to make the image clear 
(§ 4). Open the closed eye, and the image of the rule will appear as 
if on the paper at the base of the support. Hold the head very still, 
and, with dividers, get the distance between any two lines of the image. 
This is the so-called method of binocular or double vision in which the 
microscopic image is seen with one eye and the dividers with the other, 
the two images appearing to be fused in a single visual field. EXPLANATION OF PLATE IV. 
Figures showing the use of the Abbe Camera Lucida (§g 122-125). 
Fig. 30. Abbe Camera Lucida with the mirror at 45°, the drawing surface hori- 
zontal, and the microscope vertical. 
Axis, Axis. Axial ray from the microscope and from the drawing surface. 
A B. Marginal rays of the field on the drawing surface, a b. Sectional view of the 
silvered surface in the lower of the triangular prisms composing the cubical prism 
(P). The silvered surface is shown as incomplete in the center, thus giving pas- 
sage to the rays from the microscope. 
Foot. Foot or base of the microscope. 
G. Smoked glass seen in section. It is placed between the mirror and the prism 
to reduce the light from the drawing surface. 
Mirror. The mirror of the camera lucida. A quadrant (Q) has been added to 
indicate the angle of inclination of the mirror, which in this case is 450. 
Ocular. Ocular of the microscope over which the prism of the camera lucida is 
placed. 
P, P. Drawing pencil and the cubical prism over the ocular. 
Fig. 31. Geometrical figure showing the angles made by the axial ray with the 
drawing surface and the mirror. 
A B. The drawing surface. 
Fig. 32. The Abbe Camera Lucida with the mirror at 350, and the position of the 
drawing surface to avoid distortion ($ 124). 
Axis, Axis. Axial ray from the microscope and from the drawing surface. 
A B. Drawing surface raised toward the microscope 20°. 
Foot. The foot or base of the microscope. 
Mirror with quadrant (Q). The mirror is seen to be at an angle of 350. 
Ocular. Ocular of the microscope. 
P, P. Drawing pencil, and the cubical prism over the ocular. 
W. Wedge to support the drawing board. 
Fig. 33. Geometrical figure of the preceding, showing the angles made by the 
axial ray with the mirror and the necessary elevation of the drawing board to avoid 
distortion. From the equality of opposite angles, the angle of the axial ray reflect- 
ed at 350 must make an angle of 1 io° with a horizontal drawing board. The board 
must then be elevated toward the microscope 20° in order that the axial ray mav 
be perpendicular to it, and thus fulfill the requirements necessary to avoid distor- 
tion (?$ 120, 124). 
Fig. 34. This shows the arrangement of the drawing surface for a mirror at 350 
and the microscope inclined 30° (Mrs. Gage). ($ 125). 
Fig. 35. Upper view of the prism of the camera lucida. A considerable portion 
of the face of the prism is covered, and the opening in the silvered surface appears 
oval. 
Fig. 36. Ocular, showing eye-point, E P. It is at this point both horizontally 
and vertically that the hole of the silvered surface should be placed ($ 123). 
Fig- 37- Quadrant to be attached to the mirror of the Abbe Camera Lucida to 
indicate the angle of the mirror. As the angle is nearly always at 450, 40° or 350, 
only those angles are shown. MAGNIFICATION AND DR A WING. 
37 
MAGNIFICATION AND DRAWING. 
§ 99. Measuring the Spread of Dividers.—This should be done 
on a steel scale divided to millimeters and yths. 
As \ mm. cannot be see plainly by the unaided eye, place one arm of 
the dividers at a centimeter line, and then with the tripod magnifier 
count the number of spaces on the rule included between the points of 
the dividers. The magnifier simply makes it easy to count the spaces 
on the rule included between the points of the dividers—it does not, of 
course, increase the number of spaces or change their value. 
As the distance between any two lines of the image of the scale gives 
the size of the virtual image (PI. I, Fig. 4, A' B'), and as the size of 
the object is known, the magnification is determined by dividing the 
size of the image by the size of the object. Thus, suppose the distance 
between the two lines of the image is measured by the dividers and 
found on the steel scale to be 15 millimeters, and the actual size of the 
space between the two lines of the object is 2 millimeters, then the 
magnification must be 15-4-2=7)4. That is, the image is 7 )4 times as 
long or wide as the object. In this case the image is said to be magni- 
fied 7)4 diameters, or 7)4 times linear. 
The magnification of any simple magnifier may be determined ex- 
perimentally in the way described for the tripod. 
MAGNIFICATION OF A COMPOUND MICROSCOPE. 
§ ioo. The Magnification of a Compound Microscope is the 
ratio between the final or virtual image (PI. I, Fig 5, B A), and the 
object magnified (PI. I, Fig. 5, A3 B3). 
The determination of the magnification of a compound microscope 
may be made as with a simple microscope (§ 98), but this is very fa- 
tiguing and unsatisfactory. 
§ 101. Stage, Object or Objective Micrometer.—For determining 
the magnification of a compound microscope and for the purposes of 
micrometry it is necessary to have a finely divided scale or rule on glass 
or on metal. Such a finely divided scale is called a micrometer, and for 
ordinary work one on glass is most convenient. The spaces between 
the lines should be y and millimeter, and when high powers are 
to be used the lines should be very fine. It is of advantage to have the 
coarser lines filled with graphite (plumbago), especially when low pow- 
ers are to be used. If one has an uncovered micrometer the lines may 
be very readily filled by rubbing some of the plumbago on the surface 
with the end of a cork, the superfluous plumbago may be removed by 
using a clean dry cloth or a piece of the Japanese paper. After the 
lines are filled and the plumbago wiped from the surface, the slide 38 
MAGNIFICATION AND DRAWING. 
should be examined and if it is found satisfactory, i. e., if the lines are 
black, a cover-glass on which is a drop of warm balsam may be put 
over the lines to protect them. 
§ 102. Determination of Magnification.—This is most readily ac- 
complished by the use of some form of camera lucida (§§ 121, 122), 
that of Wallaston being most convenient as it may be used for all pow- 
ers, and the determination of the standard distance of 250 millimeters 
at which to measure the image is very readily determined (PI. Ill, 
Fig- 27, § 104). 
Employ the 18 mm. in.) objective and a 50 mm. (2 in., A or No. 
1) ocular and stage micrometer as object. For this power the Xyth mm. 
spaces of the micrometer should be used as object. Focus sharply, and 
make the body of the microscope horizontal, by bending the flexible 
pillar, being careful not to bring any strain upon the fine adjustment 
(§ 7E Fig. 10). 
Put a Wallaston’s camera lucida (§ 121) in position, and turn the 
ocular around if necessary so that the broad flat surface may face di- 
rectly upward as shown in Fig. 27. Elevate the microscope by putting 
a block under the base, so that the perpendicular distance from the up- 
per surface of the camera lucida to the table is 250 mm. (§ 104). Place 
some white paper on the work-table beneath the camera lucida. 
Close one eye, and hold the head so that the other may be very close 
to the camera lucida. Look directly down. The image will appear to 
be on the table. It may be necessary to readjust the focus after the 
camera lucida is in position. If there is difficulty in seeing dividers and 
image consult §121. Measure the image with dividers and obtain the 
power exactly as above (§§ 98, 99). 
Thus : Suppose two of the mm. spaces were taken as object, and 
the image is measured by the dividers, and the spread of the dividers 
is found on the steel rule to be 9f millimeters. If now the object is yyths 
of a millimeter and the magnified image is 9! millimeters the magnifi- 
cation (which is the ratio between size of object and image) must be 
9f -f- y\ = 47. That is, the magnification is 47 diameters or 47 times 
linear. If the fractional numbers in the above example trouble the stu- 
dent, both may be reduced to the same denomination, thus : If the size 
of the image is found to be gi mm. this number may be reduced to tenths 
mm. so it will be of the same denomination as the object. In 9 mm. 
there are 90 tenths, and in £ there are 4 tenths, then the whole length 
of the image is 90 -f 4 = 94 tenths of a millimeter. The object is 2 
tenths of a millimeter, then there must have been a magnification of 
94 -4- 2 = 47 diameters in order to produce an image 94 tenths of a mil- 
limeter long. 
Put the 25 mm. (1 in. C or No. 4) ocular in place of one of 50 mm. 39 
MAGNIFICATION AND DR A WING. 
Focus, and then put the camera lucida in position. Measure the size 
of the image with dividers and a rule as before. The power will be 
considerably greater than when the low ocular was used. This is be- 
cause the virtual image (Fig. 5, B' A'),- seen with the high ocular is 
larger than the one seen with the low one. The real image (Fig. 5, A 
B), remains nearly the same, and would be just the same if positive, 
par-focal oculars (§§ 21, 48 note), were used. 
Lengthen the body of the microscope 50-60 mm. by pulling out the 
draw-tube. Remove the camera lucida, and focus, then replace the 
camera, and obtain the magnification. It will be greater than with the 
shorter body. This is because the real image (Fig. 5, B A) is formed 
farther from the objective when the body is lengthened, and being 
formed farther from the objective it must necessarily be larger (§ 7 and 
Fig. 28). 
§ 103. Varying the Magnification of a Compound Microscope. 
It will be seen from the above experiments (§ 102), that independently 
of the distance at which the microscopic image is measured (§ 104), 
there are three ways of varying the power of a compound microscope. 
These are named below in the order of desirability. 
(1) By using a higher or lower objective. 
(2) By using a higher or lower ocular. 
(3) By lengthening or shortening the hibe of the microscope.* 
§ 104. Standard Distance of 250 Millimeters at which the Vir- 
tual Image is Measured.—For obtaining the magnification of both 
the simple and the compound microscope the directions were to measure 
the virtual image at a distance of 250 millimeters. This is not that the 
image could not be seen and measured at any other distance, but be- 
cause some standard must be selected, and this is the most common 
one. The necessity for the adoption of some common standard will be 
seen at a glance in PI. Ill, Fig. 28, where is represented 
the fact that the size of the virtual image depends directly on the dis- 
tance at which it is projected, and this size is directly proportional to 
the vertical distance from the apex of the triangle, of which it forms a 
base. The distance of 250 millimeters has been chosen on the suppo- 
sition that it is the distance of most distinct vision for the normal 
human eye. 
* Amplifier.—In addition to the methods of varying the magnification given in 
§ 103, tlje magnification is sometimes increased by the use of an amplifier, that is 
a diverging lens or combination placed between the objective and ocular and serv- 
ing to give the image forming rays from the objective an increased divergence. 
This accessory was first made effective by Tolies, who made it in the form of a 
small achromatic concavo-convex lens to be screwed into the lower end of the 
draw-tube (PI. II, Fig. 10) and thus but a short distance above the objective. The 
divergence given the rays increases the size of the real image about two fold. 40 
MAGNIFICATION AND DRAWING. 
Demonstrate the difference in magnification due to the distance at 
which the image is projected, by raising the microscope so that the dis- 
tance will be 350 millimeters, then 150 millimeters. 
In preparing drawings it is often of great convenience to make them 
at a distance somewhat less or somewhat greater than the standard. In 
such a case the magnification must be determined for the special dis- 
tance. 
It may be remarked further that if spectacles are not used, a near- 
sighted (myopic) person would obtain a somewhat greater, and a far- 
sighted (presbyopic) person a somewhat less magnification for the same 
instrument at the standard distance. This is because the eye of the 
observer forms an integral optical part of the microscope at the time of 
observation, and the equivalent focus of the myopic eye is less than 
normal and that of the presbyopic eye greater (§ 7). 
For discussions of the magnification of the microscope, see : B., pp. 
41, 355 5 C., pp. 161, 206 ; N. & S., p. 176 ; R., p. 29 ; Robin, p. 126 ; 
Amer. Soc. Micrs., 1884, p. 183; 1889, p. 22; Amer. Jour. Arts and 
Sciences, 1890, p. 50; Jour. Roy. Micr. Soc., 1888, 1889. 
§ 105. Table of Magnifications and of the Valuations of the 
Ocular Micrometer.— The following table should be filled out by each 
student. In using it for Micrometry and Drawing it is necessary to keep 
clearly hi mind the exact conditions under which the determinations were 
made, and also the ways in which variation in magnification and the val- 
uation of the ocular micrometer may be produced (§§ 103, 104, 114, 116). 
OCULAR OCULAR 
50 mm. 25 mm. 
w -» 
Object- 
ive. 
Tube 
in. 
[Tube 
out 
MM. 
Tube 
IN. 
Tube 
out 
MM. 
Ocuear Micrometer 
Vaeuation. 
TUBE IN. OUT MM. 
y, 18 mm. 
X 
X 
X 
X 
Vs, 3 mm. 
X 
X 
X 
X 
X 
X 
X 
X 
Simpee Microscope. X 
micrometry. 
§ 106. Micrometry is the determination of the size of objects by 
the aid of a microscope. [Table from page 40 of the Microscope and Histology, Part I.] 
§ 105. Table of Magnifications and of the Valuations of the 
Ocular Micrometer.— The following table should be filled out by each 
student. In using it for Micrometry and Drawing it is necessary to keep 
clearly in mind the exact conditions under which the determinations were 
made, and also the ways in which variation in magnification and the val- 
uation of the ocular micrometer may be produced (§§ 103, 104, 114, 116). 
OCULAR OCULAR 
50 mm. - 25 mm. 
w ' 
Object- 
ive. 
Tube 
in. 
Tube 
out 
MM. 
Tube 
IN. 
Tube 
OUT 
MM. 
Ocuear Micrometer 
Valuation. 
TUBE IN. OUT MM. 
18 mm. 
X 
X 
X 
X 
H, 3 mm- 
X 
X 
X 
♦ 
X 
X 
X 
X 
X 
Simple Microscope. 
X 
Each student should fill out this table and hand it in as a part of his 
weekly report. In this report, the results are to be given in the table, 
but this must be accompanied with the full work and explanations on 
extra sheets. 
S. H. GAGE. 41 
MAGNIFICA TION AND DR A WING. 
MICROMETRY WITH THE SIMPEE MICROSCOPE. 
§ 107. With a simple microscope, (A) the easiest and best way is to 
use dividers and then the simple microscope to see when the points of 
the dividers exactly include the object. The spread of the dividers is 
then obtained as above (§ 99). This amount will be the actual size of 
the object, as the microscope was only used in helping to see when the 
divider points exactly enclosed the object, and then for reading the di- 
visions on the rule in getting the spread of the dividers. 
(B) One may put the object under the simple microscope and then as 
determining the power (§ 98), measure the image at the standard dis- 
tance. If now the size of the image so measured is divided by the 
magnification of the simple microscope, the quotient will give the 
actual size of the object. 
Use a fly’s wing or some other object of about that size and try to 
determine the width in the two ways described above. If all the work 
is accurately done the results will agree. 
MICROMETRY WITH THE COMPOUND MICROSCOPE. 
There are several ways of varying excellence for obtaining the size 
of objects with the compound microscope, the method with the ocular 
micrometer (§§ 116, 117) being most accurate. 
§ 108. Unit of Measure in Micrometry.—As most of the objects 
measured with the compound microscope are smaller than any of the 
originally named divisions of the meter, and the common or decimal 
fractions necessary to express the size are liable to be unnecessarily 
cumbersome, Harting, in his work on the microscope (1859), proposed 
the one thousandth of a millimeter mm. or 0.001 mm.) or 
one millionth of a meter (ymnhiinr or 0.000001 meter) as the unit. 
He named this unit micro-millimeter and designated it mmm. In 
1869, Listing (Carl’s Repetorium fur Experimental-Physik, Bd. X, 
P. 5) favored the thousandth of a millimeter as unit and introduced the 
name Mikron or micrum. In English it is most often written Micron, 
plural micra or microns, pronunciation Mic'ron, or Mi'crSn. By uni- 
versal consent the sign or abbreviation used to designate it is the Greek 
}jl. Adopting this unit and sign, one would express five thousandths of 
a millimeter or o.oo5ths mm.) thus, 5/u..* 
*The term Micromillimeter ab. mmm. is very cumbersome, and besides is en- 
tirely inappropriate since the adoption of definite meanings for the prefixes micro 
and mega, meaning respectively one millionth and one million times the unit be- 
fore which it is placed. A micromillimeter would then mean one-millionth of a 
millimeter, not one-thousandth. The term micron, has been adopted by the great 
microscopical societies, the international commission on weights and measures and 
by original investigators, and is in the opinion of the writer the best term to em- 
ploy. Jour. Roy. Micr. Soc., 1888, p. 502 ; Nature, Vol. XXXVII, (1888), p. 388. 42 
MAGNIFICA TION AND DR A WING. 
£ 109. Micrometry by the use of a stage micrometer on which to mount the ob- 
ject.—In this method the object is mounted on a micrometer and then put under 
the microscope and the number of spaces covered by the object is read off directly. 
It is exactly like putting any large object on a rule and seeing how many spaces of 
the rule it covers. The defect in the method is that it is impossible to properly 
arrange objects on the micrometer. Unless the objects are circular in outline they 
are liable to be oblique in position and in every case the end or edges of the object 
may be in the middle of a space instead of against one of the lines, consequently 
the size must be estimated or guessed at rather than really measured. 
§ no. Micrometry by dividing the size of the image by the magnifi- 
cation of the microscope.—For example, employ the 3 mm. objective, 25 
mm. ocular, and a Necturus’ red blood-corpuscle preparation as object.* 
Obtain the size of the image of the long and short axes of three cor- 
puscles with the camera lucida and dividers exactly as in obtaining the 
magnification of the microscope (§ 102). Divide the size of the image 
in each case by the magnification and the result will be the actual size 
of the blood-corpuscle. Thus, suppose the image of the long axis of 
the corpuscle is 18 mm. and the magnification of the microscope 400 
diameters (§ 97), then the actual length of this long axis of the cor- 
puscle is 18 mm. -1-400= .045 mm. or 45 n (§ 108). 
§ in. Micrometry by the use of a Stage Micrometer and a Camera 
Liicida.—Employ the same object, objective and ocular as before. Put 
the camera lucida in position, and with a lead pencil make dots on the 
paper at the limits of the image of the blood-corpuscle. Measure the 
same three that were measured in § 11 o. 
Remove the object, place the stage micrometer under the microscope, 
focus well, and draw the lines of the stage micrometer so as to include 
the dots representing the limits of the part of the image to be meas- 
ured. As the value of the spaces 011 the stage micrometer is known, 
the size of the object is determined by the number of spaces of the mi- 
crometer required to include it. 
This simply enables one to put the image of a fine rule on the image 
of a microscopic object. It is theoretically an excellent method, and 
nearly the same as measuring the spread of the dividers with a simple 
microscope (§§ 99, 117). 
OCULAR MICROMETER. 
§ 112. Ocular Micrometer, Eye-Piece Micrometer.—This, as 
the name implies, is a micrometer to be used with the ocular. It is a 
* As the same three blood corpuscles are to be measured in three ways, it is an 
advantage to put a delicate ring around a group of three or more corpuscles and 
make a sketch of the whole enclosed group, marking on the sketch the corpuscles 
measured. The different corpuscles vary considerably in size, so that accurate com- 
parison of different methods of measurement can only be made when the same 
corpuscles are measured in each of the ways. MAGNIFICATION AND DR A WING. 
43 
micrometer on glass, and the lines are sufficiently coarse to be clearly 
seen by the ocular. The lines should be equidistant and about yg-tli or 
mm. apart and every fifth line should be longer and heavier to facili- 
tate counting. If the micrometer is ruled in squares (net-micrometer) 
it will be very convenient for many purposes. 
The ocular micrometer is placed in the ocular, no matter what the 
form of the ocular (i. e., whether positive or negative), at the level at 
which the real image is formed by the objective, and the image appears 
to be immediately upon or under the ocular micrometer and hence the 
number of spaces on the ocular micrometer required to measure the 
real image may be read off directly. This is measuring the size of the 
real image, however, and the actual size of the object can only be de- 
termined by determining the ratio between the size of the real image 
and the object. In other words it is necessary to get the valuation of 
the ocular micrometer in terms of a stage micrometer. 
§ 113. Valuation of the Ocular Micrometer.—This is the value 
of the divisions of the ocular micrometer for the purposes of microm- 
etry, and is entirely relative, depending upon the magnification of the 
real image formed by the objective, consequently it changes with every 
change in the magnification of the real image and must be specially 
determined for every optical combination (i. e., objective and ocular) 
and for every change in the length of the tube of the microscope. 
That is, it is necessary to determine the ocular micrometer valuation for 
every condition modifying the real image of the microscope (§ 103). 
§ 114. Obtaining the Ocular Micrometer Valuation.—As an ex- 
ample, employ the 25 mm. ocular and 18 mm. objective. Place the 
stage micrometer under the microscope for an object, and put the ocular 
micrometer in position, either through a slit in the ocular, or remove the 
eye-lens and place it upon the ocular diaphragm.* 
Tight the field well, and look into the microscope. The lines on the 
ocular micrometer should be very sharply defined. If they are not, 
raise or lower the eye-lens to make them so ; that is, focus as with the 
simple magnifier. 
When the lines of the ocular micrometer are distinct, focus the mi- 
* It is a great convenience to have a micrometer ocular (§ 25) with a spring and 
screw to enable one to accurately place the ocular micrometer. Any negative ocu- 
lar may, however, be used as a micrometer ocular by placing the ocular micrometer 
at the level of the ocular diaphragm, that is where the real image is formed. This 
is very conveniently arranged for by some opticians by a slit in the side of the ocu- 
lar, and the ocular micrometer is mounted in some way and simply introduced 
through the opening in the side. When no side opening exists the mounting of 
the ocular may be unscrewed and the ocular micrometer, if on a cover-glass, can 
be laid on the upper side of the ocular diaphragm. 44 
MAGNIFICATION AND DR A WING. 
croscope (§§ 32, 37) for the stage micrometer. The image of the stage 
micrometer will appear to be directly under or upon the ocular microme- 
ter. 
Make the lines of the two micrometers parallel by rotating the ocular, 
or changing the position of the stage micrometer, or both if necessary, 
and then make any two lines of the stage micrometer coincide with any 
two on the ocular micrometer. To do this it may be necessary to pull 
out the draw-tube a greater or less distance. See how many spaces are 
included on each of the micrometers. 
Divide the value of the included space or spaces on the stage mi- 
crometer by the number of divisions on the ocular micrometer required 
to include them, and the quotient so obtained will give the valuation of 
the ocular micrometer in fractions of the unit of measure of the stage 
micrometer. For example, suppose the millimeter is taken as the unit 
for the stage micrometer and this unit is divided into spaces of and 
yyyth millimeter. If now, with a given optical combination and tube- 
length, it requires 10 spaces on the ocular micrometer to include the 
real image of Xyth millimeter on the stage micrometer, obviously one 
space on the ocular micrometer would include only one-tenth as much, or 
y’yth mm. -T- 10 = yjj-yth mm. That is, each space on the ocular microme- 
ter would include yyyth of a millimeter on the stage micrometer, or iwth 
millimeter of length of any object under the microscope, the conditions 
remaining the same. Or in other words, it would require 100 spaces on 
the ocular micrometer to include 1 millimeter on the stage micrometer, 
then as before 1 space of the ocular micrometer would have a valuation 
of millimeter for the purposes of micrometry ; and the size of any 
minute object may be determined by multiplying this valuation of one 
space by the number of‘spaces required to include it. For example, 
suppose the fly’s wing or some part of it covered 8 spaces 011 the ocular 
micrometer, it would be known that the real size of the part measured 
is mm- X 8 == yjjyth or 80 //. (§ 108). 
§ 115. Varying the Ocular Micrometer Valuation.—Any change 
in the objective, the ocular or the tube-length of the microscope, that 
is to say any change in the size of the real image, produces a corre- 
sponding change in the ocular micrometer valuation (§ 103, 112). 
§ 116. Micrometry with the Ocular Micrometer.—Use the 3 mm. 
objective and preparation of Necturus blood corpuscles as object. 
Make certain that the tube of the microscope is of the same length as 
when determining the ocular micrometer valuation. In a word be sure 
that all the conditions are exactly as when the valuation was deter- 
mined, then put the preparation under the microscope and find the 
same three red corpuscles that were measured in the other ways (§§ 110, 
in). 45 
MAGNIFICATION AND DR A WING. 
Count the divisions on the ocular micrometer required to enclose or 
measure the long and the short axis of each of the three corpuscles, 
then multiply the number of spaces in each case by the valuation of 
the ocular micrometer for this objective, tube length and ocular, and 
the results will give the actual length of the axes of the corpuscles in 
each case. 
The same corpuscle is, of course, of the same actual size, when meas- 
ured in each of the three ways (§§ no, in, 116), so that if the meth- 
ods are correct and the work carefully enough done the same results 
should be obtained by each method. See general remarks on microm- 
etry (§ 117).* 
* There are three ways of using the ocular micrometer, or of arriving at the size 
of the objects measured with it: 
(A) By finding the value of a division of the ocular micrometer for each 
optical combination and tube-length used, and employing this valuation as a 
multiplier. This is the method given in the text and is the one most fre- 
quently employed. Thus, suppose with a given optical combination and tube- 
length it required five divisions on the ocular micrometer to include the im- 
age of yffths millimeter of the stage micrometer, then obviously one space on the 
ocular micrometer would include yth of mm. or yyth mm. ; and the size of 
any unknown object under the microscope would be obtained by multiplying the 
number of divisions on the ocular micrometer required to include its image by the 
value of one space, or in this case, 2Vth mm. Suppose some object, as the fly’s 
wing required 15 spaces of the ocular micrometer to include some part of it, then 
the actual size of this part of the wing would be 15 X 15 = fths, or 0.6 mm. 
(B) By finding the number of divisions on the ocular micrometer required to in- 
clude the image of an entire millimeter of the stage micrometer, and using this 
number as a divisor. This number is also sometimes called the ocular micrometer 
ratio. Taking the same case as in (A) suppose five divisions of the ocular microm- 
eter are required to include the image of T%ths mm., on the stage micrometer, then 
evidently it would require 5 -4- T2ff = 25 divisions on the ocular micrometer to in- 
clude a whole millimeter on the stage micrometer, then the number of divisions of 
the ocular micrometer required to measure an object divided by 25 would give the 
actual size of the object in millimeters or in a fraction of a millimeter. Thus, sup- 
pose it required 15 divisions of the ocular micrometer to include the image of some 
part of the fly’s wing, the actual size of the part included would be 15 25 = f or 
0.6 mm. This method is really exactly like the one in (A), for dividing by 25 is 
the same as multiplying by 2Vth. 
(C) By having the ocular micrometer ruled in millimeters and divisions of a 
millimeter, and then getting the size of the real image in millimeters. In em- 
ploying this method a stage micrometer is used as object and the size of the image 
of one or more divisions is measured by the ocular micrometer, thus : Suppose 
the stage micrometer is ruled in and mm. and the ocular micrometer is 
ruled in millimeters and mm. Taking y2<ytk mm. on the stage micrometer as 
object, as in the other cases, suppose it requires 10 of the yyth mm. spaces or 
1 mm. to measure the real image, then the real image must be magnified j-g — 
= 5 diameters, that is the real image is five times as great in length as the ob- 
ject, and the size of an object may be determined by putting it under the micro- 46 
MAGNIFICA TION AND DR A WING. 
| 117. Remarks on Micrometry.—In using adjustable objectives (§$ 16, 63), the 
magnification of the objective varies with the position of the adjusting collar, be- 
ing greater when the adjustment is closed as for thick cover-glasses than when 
open, as for thin ones. This variation in the magnification of the objective pro- 
duces a corresponding change in the magnification of the entire microscope and 
the ocular micrometer valuation—therefore it is necessary to determine the mag- 
nification and ocular micrometer valuation for each position of the adjusting collar. 
While the principles of micrometry are simple, it is very difficult to get the ex- 
act size of microscopic objects. This is due to the lack of perfection and uni- 
formity of micrometers, and the difficulty in determining the exact limits of the 
object to be measured. Hence, all microscopic measurements are only approxi- 
mately correct, the error lessening with the increasing perfection of the apparatus 
and the skill of the observer. 
A difficulty when one is using high powers is the width of the lines of 
the micrometer. If the micrometer is perfectly accurate half the width of 
each line belongs to the contiguous spaces, hence one should measure the image 
of the space from the centers of the lines bordering the space, or as this is some- 
what difficult in using the ocular micrometer, one may measure from the inside of 
one bordering line and from the outside of the other. If the lines are of equal 
width this is as accurate as measuring from the center of the lines. Evidently it 
would not be right to measure from either the inside or the outside of both lines 
(PI. Ill, Fig. 29). 
It is also necessary in micrometry, to use an objective of sufficient power to en- 
able one to see all the details of an object with great distinctness. The necessity 
of using sufficient amplification in micrometry has been especially remarked upon 
by Richardson, Monthly Micr. Jour., 1874, 1875 ; Rogers, Proc. Amer. Soc. Micro- 
scopists, 1882, p. 239; Ewell, North American Pract., 1890, pp. 97, 173. 
As to the limit of accuracy in micrometry, one who has justly earned the right 
to speak with authority expresses himself as follows : “ I assume that 0.2H is the 
limit of precision in microscopic measures, beyond which it is impossible to go 
with certainty." W. A. Rogers, Proc. Amer. Soc. Micrs., 1883, p. 198. 
scope and getting the size of the real image in millimeters with the ocular mi- 
crometer and dividing it by the magnification of the real image, which in this 
case is 5 diameters. 
Use the fly’s wing as object as in the other cases,:and measure the image of the 
same part. Suppose that it required 30 of the mm. divisions = mm. or 3 
mm. to include the image of the part measured, then evidently the actual size of 
the part measured would be 3 mm. -4--5 = f mm., the same result as in the other 
cases. 
In comparing these methods it will be seen that in the first two (A and B) the oc- 
ular micrometer may be simply ruled with equidistant lines without regard to the 
absolute size in millimeters or inches of the spaces. In the last method the ocu- 
lar micrometer must have its spaces some known division of a millimeter or inch. 
In the first two methods only one standard of measure is required, viz., the stage 
micrometer; in the last methods two standards must be used,—a stage micrometer 
and an ocular micrometer. Of course the ocular micrometer in the first two cases 
must have the lines equidistant as well as in the last case, but ruling lines equi- 
distant and an exact division of a millimeter or an inch are two quite different 
matters. 47 
MAGNIFICA TION AND DR A WING. 
In comparing the methods of micrometry with the compound microscope, given 
above 109, no, in, 116) the one given in § 109 is impracticable, that given in \ 
no is open to the objection that two standards are required,—the stage microme- 
ter, and the steel rule ; it is open to the further objection that several different 
operations are necessary, each operation adding to the probability of error. Theo- 
retically the method given in $ in is good, but it is open to the very serious ob- 
jection in practice that it requires so many operations which are especially liable to 
introduce errors. The method that experience has found most safe and expedi- 
tious, and applicable to all objects, is the method with the ocular micrometer. If 
the valuation of the ocular micrometer has been accurately determined, then the 
only difficulty is in deciding on the exact limits of the object to be measured and 
so arranging the ocular micrometer that these limits are inclosed by some divisions 
of the micrometer. Where the object is not exactly included by whole spaces on 
the ocular micrometer, the chance of error comes in, in estimating just how far 
into a space the object reaches on the side not in contact with one of the microm- 
eter lines. If the ocular micrometer has some quite narrow spaces, and others 
considerably larger, one can nearly always manage to exactly include the object 
by some two lines. 
For those especially interested in micrometry, as in its relation to medical juris- 
prudence, the following references are recommended. These articles consider the 
problem in a scientific as well as a practical spirit: The papers of Prof. Wm. A. 
Rogers on micrometers and micrometry in the Amer. Quar. Micr. Jour., Vol. I, 
pp. 97, 208; Proceedings Amer. Soc. Microscopists, 1882, 1883, 1887. Dr. M. D. 
Ewell, Proc. Amer. Soc. Micrs., 1890 ; The Microscope, 1889, pp. 43-45 ; North 
Amer. Pract., 1890, pp. 97, 173. Dr. J. J. Woodward, Amer Jour, of the Med. Sci., 
1875. M. C. White, Article Blood-stains, Ref. Hand-Book, Med. Sciences, 1885. 
For the change in magnification due to a change in the adjustment of adjustable 
objectives, see Jour. Roy. Micr. Soc., 1880, p. 702 ; Amer. Monthly Micr. Jour., 
1880, p. 67. 
DRAWING WITH THE MICROSCOPE. 
| 118. Microscopic objects may be drawn free-hand directly from the micro- 
scope, but in this way a picture giving only the general appearance and relations 
of parts is obtained. For pictures which shall have all the parts of the object in 
true proportions and relations, it is necessary to obtain an exact outline of the 
image of the object, and to locate in this outline all the principal details of struc- 
ture. It is then possible to complete the picture free hand from the appearance 
of the object under microscope. The appliance used in obtaining outlines, etc., of 
the microscopic image is known as a camera lucida. 
I 119. Camera Lucida.—This is an optical apparatus for enabling one to see ob- 
jects in greatly different situations, as if in one field of vision, and with the same 
eye. In other words, it is an optical device for superimposing or combining two 
fields of view in one eye. 
As applied to the microscope, it causes the magnified virtual image of the ob- 
ject under the microscope to appear as if projected upon the table or drawing 
board, where it is visible with the drawing paper, pencils, dividers, etc., by the 
same eye, and in the same field of vision. The microscopic image appears like a 
picture on the drawing paper. This is accomplished in two distinct ways : 
(A) By a camera lucida reflecting the rays from the microscope so that their di- 
rection when they reach the eye coincides with that of the rays from the drawing 48 
MAGNIFICA TION AND DR A WING. 
paper, pencils, etc. In some of the camera lucidas of this group (Wollaston’s 
PI. Ill, Fig. 27), the rays are reflected twice and the image appears as when look- 
ing directly into the microscope. In others, the rays are reflected but once and 
the image has the inversion produced by a plane mirror. For drawing purposes 
this inversion is a great objection, as it is necessary to similarly invert all the de- 
tails added free-hand. 
(B) a camera lucida reflecting the rays of light from the drawing paper, etc., 
so that their direction when they reach the eye coincides with the direction of the 
rays from the microscope (PI. IV, Fig. 30, 32). In all of the camera lucidas of 
this group, the rays from the paper are twice reflected and no inversion appears. 
The better forms of camera lucidas (Wollaston’s, Grunow’s, Abbe’s, etc.), may 
be used for drawing both with low and with high powers. Some require the mi- 
croscope to be inclined (Fig. 27), while others are designed to be used on the 
microscope in a vertical position. As in biological work it is often necessary to 
have the microscope vertical, this form is to be preferred. [ (B. 31, 355), (Beh. 
no), (C. 112), Car. 73), (J. R. M. S. nearly every volume). For drawing at a mag- 
nification of from 5 to xoo diameters for large objects see (W. 132), (J. R. M. S. 
1881, p. 819; 1882, p. 402; 1884, p. 115 ; 1888, p. 113), (Amer. Naturalist, 1886, p. 
1071 ; 1887, pp. 1040, 1043)]. 
§ 120. Avoidance of Distortion.—In order that the picture drawn 
by the aid of a camera lucida may not be distorted, it is necessary that 
the axial ray from the image on the drawing surface shall be at right 
angles to the drawing surface (PI. Ill, Fig. 27, PI. IV). 
\ 121. Wollaston’s Camera Lucida.—This is a quadrangular prism of glass put 
in the path of the rays from the microscope, and serves to change the direction of 
the axial ray 90 degrees. In using it the microscope is made horizontal, and the 
rays from the microscope enter one half of the pupil while rays from the drawing 
surface enter the other half of the pupil. As seen in the figure (PI. Ill, Fig. 27) 
the fields party overlap, and where they do so overlap, pencil or dividers and mi- 
croscopic image can be seen together. 
In drawing or using the dividers with the Wollaston camera lucida it is neces- 
sary to have the field of the microscope and the drawing surface about equally 
lighted. If the drawing surface is too brilliantly lighted the pencil or dividers 
may be seen very clearly but the microscopic image will be obscure. On the 
other hand, if the field of the microscope has too much light the microscopic im- 
age will be very definite, but the pencil or dividers will not be visible. Again, as 
rays from the microscope and from the drawing surface must enter independent 
parts of the pupil of the same eye, one must hold the eye so that the pupil is 
partly over the camera lucida and partly over the drawing surface. One can tell 
the proper position by trial. This is not a very satisfactory camera to draw with, 
but it is a very good form to measure the vertical distance of 250 mm. at which 
the drawing surface should be placed when determining magnification ($ 104). 
§ 122. Abbe Camera Lucida.—This consists of a cube of glass cut 
into two triangular prisms and silvered on the lower one. A small oval 
hole is then cut out of the center of the silvered surface and the two 
prisms are cemented together, thus giving a cubical prism with a perfor- 
ated 45-degree mirror (PI. IV, Fig. 30, a b). The upper surface of the 
prism is covered by a perforated metal plate (Fig. 35). This prism is 
placed over the ocular in such a way that the light from the microscope 49 
MAGNIFICA TION AND DR A WING. 
passes through the hole in the silvered face and thence directly to the 
eye. Light from the drawing surface is reflected by a mirror to the sil- 
vered surface of the prism and reflected by this surface to the eye in 
company with the rays from the microscope, so that the two fields ap- 
pear as one, and the image is seen as if on the drawing surface (Fig. 
30). It is designed for use with a vertical microscope, but see § 124. 
§ 123. Arrangement of the Camera Lucida Prism.—In placing 
this camera lucida over the ocular for drawing or the determination of 
magnification, the center of the hole in the silvered surface is placed in 
the optic axis of the microscope. This is done by properly arranging 
the centering screws that clamp the camera to the microscope tube or 
ocular. The perforation in the silvered surface must also be at the level 
of the eye-point (Fig. 36). In other words, the prism must be so ar- 
ranged vertically and horizontally that the hole in the silvered surface 
will be co-incident with the eye -point of the ocular. If it is above or 
below or to one side, part or all of the field of the microscope will be 
cut off. As stated above, the centering screws are for the proper hori- 
zontal arrangement of the prism. The prism is set at the right height 
by the makers for the eye-point of a medium ocular. If one desires to 
use an ocular with the eye-point farther away or nearer, as in using 
high or low oculars (§ 36), the position of the eye-point may be deter- 
mined as directed in § 36 and the prism loosened and raised or lowered 
to the proper level; but in doing this one should avoid setting the prism 
obliquely to the mirror. 
One can determine when the camera is in a proper position by look- 
ing into the microscope through it. If the field of the microscope ap- 
pears as a circle and of about the same size as without the camera 
lucida, then the prism is in a proper position. If one side of the field 
is dark, then the prism is to one side of the center ; if the field is con- 
siderably smaller than when the prism is turned off the ocular (§ 124) 
it indicates that it is not at the correct level, i. e., it is above or below 
the eye-point. 
§ 124. Arrangement of the Mirror and the Drawing Surface.— 
The Abbe camera lucida was designed for use with a vertical micro- 
scope (Fig. 30). On a vertical microscope, if the mirror is set at an 
angle of 450 the axial ray will be at right angles with the table top or 
a drawing board which is horizontal (Fig. 30), and a drawing made 
under these conditions would be in true proportion and not distorted. 
The stage of most microscopes, however, extends out so far at the 
sides that with a 450 mirror the image appears in part on the stage of 
the microscope. In order to avoid this the mirror may be depressed to 
some point below450, at 40° or 350 (Fig. 32, 33). But as the axial ray 
from, the mirror to the prism must still be reflected horizontally, it fol- 50 
MAGNIFICATION AND DRAWING. 
lows that the axial ray will no longer form an angle of 90 degrees with 
the drawing surface, but a greater angle. If the mirror is depressed 
to 350, then the axial ray must make an angle of no° with a hori- 
zontal drawing surface, see the geometrical figure, (Fig. 33). To make 
the angle 90° again so that there shall be no distortion, the drawing 
board must be raised toward the microscope 20°. The general rule 
is to raise the drawing board twice as many degrees toward the 
microscope as the mirror is depressed below 450. Practically the 
field for drawing can always be made free of the stage of the micro- 
scope, at 450, at 40° or at 350. In the first case (450 mirror) the draw- 
ing surface should be horizontal, in the second case (40° mirror) the 
drawing surface should be elevated io°, and in the third case (350 mir- 
ror) the drawing board should be elevated 20° toward the microscope. 
Furthermore it is necessary in using an elevated drawing board to have 
the mirror bar project directly laterally so that the edges of the mirror 
will be in planes, parallel with the edges of the drawing board, other- 
wise there will be front to back distortion, although the elevation of 
the drawing board would avoid right to left distortion. If one has a 
micrometer ruled in squares (net-micrometer) the distortion produced by 
not having the axial ray at right angles with the drawing surface may 
be very strikingly shown. For example, set the mirror at 350 and use 
a horizontal drawing board. With a pencil make dots at the corners of 
some of the squares, and then with a straight edge connect the dots. 
The figures will be considerably longer from right to left than from 
front to back. Circles in the object would appear as ellipses in the 
drawings, the major axis being from right to left. 
The angle of the mirror may be determined with a protractor, but 
that is troublesome. It is much more satisfactory to have a quadrant 
attached to the mirror and an indicator on the projecting arm of the 
mirror. If the quadrant is graduated throughout its entire extent, or 
preferably at three points, 450, 40° and 350, one can set the mirror at a 
known angle in a moment, then the drawing board can be hinged and 
the elevation of io° and 20° determined with a protractor. The draw- 
ing board is very conveniently held up bj? a broad wedge. By marking 
the Iposition of the wedge for io° and 20° the protractor need be used 
but once, then the wedge may be put into position at any time for the 
proper elevation. 
§ 125. Abbe Camera and Inclined Microscope.—It is very fatigu- 
ing to draw continuously with a vertical microscope, and many 
mounted objects admit of an inclination of the microscope, when one 
can sit and work in a more comfortable position. The Abbe camera is 
as perfectly adapted to use with an inclined as with a vertical micro- 
scope. All that is requisite is to be sure that the fundamental law is MAGNIFICA TION AND DR A WING. 
observed regarding the axial ray of the image and the drawing surface, 
viz., that they should be at right angles (PI. IV). This is very easily 
accomplished as follows : The drawing board is raised toward the mi- 
croscope twice as many degrees as the mirror is depressed below 45° 
(§ 124) then it is raised exactly as many degrees as the microscope is 
inclined and in the same direction, that is so the end of the drawing 
board shall be in a plane parallel with the stage of the microscope. 
The mirror must have its edges in planes parallel with the edges of the 
drawing board also (Fig. 34).* 
§126. Drawing with the Abbe Camera Lucida.—(A) The light 
from the microscope and from the drawing surface should be of nearly 
equal intensity so that the image and the drawing pencil can be seen 
with about equal distinctness. This may be accomplished with very low 
powers (18 mm. and lower objectives) by covering the mirror with 
white paper when transparent objects are to be drawn. When opaque 
objects, like dark insects, are to be drawn it may be necessary to con- 
centrate light upon them with a condensing lens or concave mirror. 
For high powers it is best to use an Abbe illuminator. Often the light 
may be balanced by using a larger or smaller opening in the dia- 
phragm. One can tell which field is excessively illuminated, for it is 
the one in which objects are most distinctly seen. If it is the micro- 
scopic, then the image of the microscopic object is very distinct and 
the pencil is invisible or very indistinct. If the drawing surface is too 
brilliantly lighted the pencil can be seen clearly, but the microscopic 
image will be very obscure. 
If the drawing surface is too brilliantly illuminated, it may be shaded 
by placing a book or a ground glass screen between it and the window, 
also by putting one or more smoked glasses in the path of the rays from 
the mirror (Fig. 30, G). If the light in the microscope is too intense, 
it may be lessened by using the white paper over the mirror, or by a 
ground glass screen between the microscope mirror and the source of 
light (Piersol, Amer. M. M. Jour., 1888, p. 103). It is also an excel- 
lent plan to blacken the end of the drawing pencil with carbon ink. 
Sometimes it is easier to draw on a black surface, using a white pencil 
or style. The carbon paper used in manifolding letters, etc., may be 
used, or ordinary black paper may be lightly rubbed on one side with a 
moderately soft lead pencil. Place the black paper over white paper 
and trace the outlines with a pointed style of ivory or bone. A corre- 
sponding dark line will appear on the white paper beneath. (J. R. M. 
S., 1883, p. 423). 
(A) It is desirable to have the drawing paper fastened with thumb 
* This method of using the Abbe camera lucida on an inclined microscope was 
devised by Mrs. Gage. 52 
MAGNIFICA TION AND DR A WING. 
tacks, or in some other way. (B) The lines made while using the 
camera lucida should be very light, as they are liable to be irregular. 
(C) Only outlines are drawn and parts located with a camera lucida. 
Details are put in free-hand. (D) It is sometimes desirable to draw the 
outline of an object with a moderate power and add the details with a 
higher power. If this is done it should always be clearly stated. It is 
advisable to do this only with objects in which the same structure is 
many times duplicated, as a nerve or a muscle. In such an object all 
the different structures could be shown, and by omitting some of the 
fibers the others could be made plainer without an undesirable enlarge- 
ment of the entire figure. 
(E) If a drawing of a given size is desired and it cannot be obtained 
by any combination of oculars, objectives and lengths of the body of 
the microscope, the distance between the camera lucida and the table 
may be increased or diminished until the image is of the desired size. 
The image of a few spaces of the micrometer, will give the scale of en- 
largement, or the power may be determined for the special case (§ 127). 
(F) It is of the greatest advantage, as suggested by Heinsius (Zeit. 
w. Mikr., 1889, p. 367), to have the camera lucida hinged so that the 
prism may be turned off the ocular for a moment’s glance at the pre- 
paration, and then returned in place without the necessity of loosening 
screws and readjusting the camera. This form is now made by Zeiss, 
but as yet no quadrant is added. Any skilled mechanic can add that, 
however. 
[(B. 31, 355). (Beh. (C. 112), (Fol. 70), (Frey 38), (J. R. M. S. 
1883, pp. 283, 560 ; 1886, 516 ; 1888, pp. 113, 809, 798) ; (Amer. M. M. 
Jour., 1888, p. 103; 1890, p. 94); (Z. w. M. 1884, p. 1-21 ; 1889, P- 
367)]- 
§ 127. Magnification of the Microscope and Size of Drawings 
with the Abbe Camera Lucida.—In determining the standard dis- 
tance of 250 millimeters at which to measure the image in getting the 
magnification of the microscope, it is necessary to measure from the 
point marked P on the 'prism (Fig. 30) to the axis of the mirror and 
then vertically to the drawing board. 
In getting the scale at which a drawing is enlarged the best way is to 
remove the preparation and put in its place a stage micrometer, and to 
trace a few (5 or 10) of its lines under one corner of the drawing. The 
value of the spaces of the micrometer being given, thus, 
root11 mm. 
The enlargement of the figure can then be accurately determined at 
any time by measuring with a steel scale the length of the image of 
the micrometer spaces and dividing it by their known width. 53 
MAGNIFICATION AND DR A WING. 
Thus, suppose the 5 spaces of the scale of enlargement given with a 
drawing were found to measure 25 millimeters and the spaces on the 
micrometer were millimeter, then the enlargement would be 
25 -r- = 500. That is, the image was drawn at a magnification of 
500 diameters. 
If the micrometer scale is used with every drawing, there is no need 
of troubling one’s self about the exact distance at which the drawing 
is made, convenience may settle that, as the special magnification in 
each case may be determined from the scale accompanying the picture. 
It should be remembered, however, that the conditions when the scale 
is drawn must be exactly as when the drawing was made. CHAPTER IV. 
MICRO-SPECTROSCOPE AND POEARISCOPE. 
Compound microscope (Ch. I); Micro-spectroscope (g 128); Watch-glasses and 
small vials, slides and covers (gg 143, 144) ; Various substances for examination 
(as blood and ammonium sulphide, permanganate of potash, chlorophyll, some 
colored fruit, etc. (gg 144-145); Micro-polarizer (g 150); Selenite plate (gi57f-); Var- 
ious doubly refracting objects, as crystals, textile fibers, starch, section of bone, etc. 
APPARATUS AND MATERIAL REQUIRED FOR THIS CHAPTER. 
MICRO-SPECTROSCOPE. 
| 128.—A Micro-Spectroscope, Spectroscopic, or Spectral Ocular, is a direct 
vision spectroscope in connection with a microscopic ocular. The one devised by 
Abbe and made by Zeiss consists of a direct vision spectroscope prism of the 
Amici pattern, and of considerable dispersion, placed over the ocular of the micro- 
scope. This direct vision or Amici prism consists of a single triangular prism of 
heavy flint glass in the middle and one of crown glass on each side, the edge of 
the crown glass prisms pointing toward the base of the flint glass prism, i. e., the 
edges of the crown and flint glass prisms point in opposite directions. The flint 
glass prism serves to give the dispersion or separation into colors, while the crown 
glass prisms serve to make the emergent rays parallel with the incident rays, so 
that one looks directly into the prism along the axis of the microscope. 
The Amici prism is in a special tube which is hinged to the ocular and held in 
position by a spring. It may be swung free of the ocular. I11 connection with 
the ocular is the slit mechanism and a prism for reflecting horizontal rays verti- 
cally for the purpose of obtaining a comparison spectrum (§ 137). Finally near 
the top is a lateral tube with mirror for the purpose of projecting an Angstrom 
scale of wave lengths upon the spectrum (§ 138). 
§ 129. Various Kinds of Spectra.—By a spectrum is meant the colored bauds 
appearing when light traverses a dispersing prism or a diffraction grating, or is af- 
fected in any way to separate the different wave lengths of light into groups. 
When daylight or some good artificial light is thus dispersed one gets the appear- 
ance so familiar in the rain-bow. 
(A) Continuous Spectrum.—In case a good artificial light or the electric light is 
used the various rain-bow or spectral colors merge gradually into one another in 
passing from end to end of the spectrum. There are no breaks or gaps. 
(B) Line Spectrum.—If a gas is made incandescent the spectrum it produces 
consists, not of the various rain-bow colors, but of sharp, narrow, bright lines, the 
color depending on the substance. All the rest of the spectrum is dark. These 
line spectra are very strikingly shown by various metals heated till they are in 
the form of incandescent vapor. 
(C) Absorption Spectrum.—By this is meant a spectrum in which there are 
dark lines or bands in the spectrum. The most striking and interesting of the 
absorption spectra is the Solar Spectrum, or spectrum of sun-light. If this is ex- 
amined carefully it will be found to be crossed by dark lines, the appearance be- 55 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
ing as if one were to draw pen marks across a continuous spectrum at various 
levels, sometimes apparently between the colors and sometimes in the midst of a 
color. These dark lines are the so-called Fraunhofer Tines. Some of the princi- 
pal ones have been lettered with Roman capitals, A. B. C. D. E. F. G. H., com- 
mencing at the red end. The meaning of these lines was for a long time enig- 
matical, but it is now known that they correspond with the bright lines of a line 
spectrum (B). For example, if sodium is put in the flame of a spirit lamp it will 
vaporize and become luminous. If this light is examined there will be seen one 
or two bright yellow bands corresponding in position with D of the solar spectrum 
(PI. V, Fig. 45). If now the spirit lamp-flame, colored by the incandescent so- 
dium, is placed in the path of the electric light, and the light examined as before, 
there will be a continuous spectrum, except dark lines in place of the bright 
sodium lines. That is, the comparatively cool yellow light of the spirit lamp cuts 
off or absorbs the intensely hot yellow light of the electric light; and although 
the spirit flame sends yellow light to the spectroscope it is so faint in comparison 
with the electric light that the sodium lines appear dark. It is believed that in 
the sun’s atmosphere there are incandescent metal vapors (sodium, iron, etc.) 
but that they are so cool in comparison with the rays of their wave length in the 
sun that the cooler light of the incandescent metallic vapors absorbs the light of 
corresponding wave length, and are, like the spirit lamp-flame, unable to make up 
the loss, and therefore the presence of the dark lines. 
Absorption spectra from colored substances.—While the solar spectrum is an 
absorption spectrum, the term is more commonly applied to the spectra obtained 
with light which had passed through or has been reflected from colored objects 
which are not self-luminous. 
It is the special purpose of the micro-spectroscope to investigate the spectra of 
colored objects which are not self luminous, as blood and other liquids, various 
minerals, as malazeit, etc. The spectra obtained by examining the light reflected 
from these colored bodies or transmitted through them, possess, like the solar 
spectrum, dark lines or bands, but the bands are usually much wider and less 
sharply defined. Their number and position depend on the substance or its con- 
stitution (PI. V, Fig. 45), and their width, in part, upon the thickness of the body. 
With some colored bodies, 110 definite bands are present. The spectrum is simply 
restricted at one or both ends and various of the other colors are considerably 
lessened in intensity. This is true of many colored fruits. 
\ 130. Angstrom and Stokes Law of Absorption Spectra.—The wave lengths of 
light absorbed by a body when light is transmitted through some of its substances 
are precisely the waves radiated from it when it becomes self-luminous. For ex- 
ample, a piece of glass that is yellow when cool, gives out blue light when it is 
hot enough to be self luminous. Sodium vapor absorbs twTo bands of yellow light 
(D lines) ; but when light is not sent through it, but itself is luminous and exam- 
ined as a source of light its spectrum gives bright sodium lines, all the rest of the 
spectrum being dark. 
§ 131. Law of Color.—The light reaching the eye from a colored, solid, liquid 
or gaseous body lighted with white light, will be that due to white light less the 
light waves that have been absorbed by the colored body. Or in other words, it 
will be due to the wrave lengths of light that finally reach the eye from the object. 
For example, a thin layer of blood under the microscope will appear yellowdsh 
green, but a thick layer will appear pure red. If now7 these two layers are exam- 
ined with a micro-spectroscope, the thin layer will show all the colors, but the red 56 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
end will be slightly, and the blue end considerably restricted, and some of the 
colors will appear of considerably lessened intensity. Finally there may appear 
two shadow-like bands, or if the layer is thick enough, two well-defined dark 
bands in the green (§ 146). 
If the thick layer is examined in the same way, the spectrum will show only 
red with a little orange light, all the rest being absorbed. Thus the spectroscope 
shows which colors remain, in part or wholly, and it is the mixture of this remain- 
ing or unabsorbed light that gives color to the object. 
§ 132. Complementary Spectra.—While it is believed that Angstrom’s law ($ 130) 
is correct, there are many bodies on which it cannot be tested, as they change in 
chemical or molecular constitution before reaching a sufficiently high temperature 
to become luminous. There are compounds, however, like those of didymium, 
erbium and terbium, which do not change with the heat necessary to render them 
luminous, and with them the incandescence and absorption spectra are mutually 
complementary, the one presenting bright lines where the other presents dark 
ones (Daniell). 
ADJUSTING THE MICROSPECTROSCOPE. 
§ 133- The micro-spectroscope or spectroscopic ocular is put in the 
place of the ordinary ocular of the microscope, and clamped to the top 
of the tube by means of a screw for the purpose. 
§ 134. Adjustment of the Slit.—In place of the ordinary dia- 
phragm with circular opening, the spectral ocular has a diaphragm 
composed of two movable knife edges by which a slit-like opening of 
greater or less width and length may be obtained at will by the use of 
screws for the purpose. To adjust the slit depress the lever holding 
the prism-tube in position over the ocular, and swing the prism aside. 
One can then look into the ocular. The lateral screw should be used 
and the knife edges approached till they appear about half a millimeter 
apart. If now the Amici prism is put back in place and the micro- 
scope well lighted, one will see a spectrum by looking into the upper 
end of the spectroscope. If the slit is too wide, the colors will over- 
lap in the middle of the spectrum and be pure only at the red and blue 
ends ; and the Fraunhofer or other bands in the spectrum will be faint 
or invisible. Dust on the edges of the slit gives the appearance of 
longitudinal streaks on the spectrum. 
§ 135. Mutual arrangement of Slit and Prism.—In order that 
the spectrum may appear as if made up of colored bands going directly 
across the long axis of the spectrum, the slit must be parallel with the 
refracting edge of the prism. If the slit and prism are not thus mu- 
tually arranged, the colored bands will appear oblique and the whole 
spectrum may be greatly narrowed. If the colored bands are oblique, 
grasp the prism tube and slowly rotate it to the right or to the left until 
the various colored bands extend across the spectrum. 
§ 136. Focusing the Slit.—In order that the lines or bands in the 
spectrum shall be sharply defined, the eye-lens of the ocular should be 57 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
accurately focused on the slit. The eye-lens is movable, and when the 
prism is swung aside it is very easy to focus the slit as one focused, for 
the ocular micrometer (§ 114). If one now uses daylight there will be 
seen in the spectrum the dark Fraunhofer lines (PI. V, Fig. 45, E. F., 
etc.). 
To show the necessity of focusing the slit, move the eye-lens down 
or up as far as possible, and the Fraunhofer lines cannot be seen. 
While looking into the spectroscope move the ocular lens up or down 
and when it is focused the Fraunhofer lines will reappear. As the 
different colors of the spectrum have different wave lengths, it is neces- 
sary to focus the slit for each color if the sharpest possible pictures are 
desired. 
§ 137. Comparison or Double Spectrum.—In order to compare 
the spectra of two different substances it is desirable to be able 
to examine their spectra side by side. This is provided for in the 
the better forms of micro-spectroscopes by a prism just below the slit, 
so placed that light entering it from a • mirror at the side of the drum 
shall be totally reflected in a vertical direction, and thus parallel with 
the rays from the microscope. The two spectra wrill be side by side 
with a narrow dark line separating them. If now the slit is well fo- 
cused and daylight be sent through the microscope and into the side to 
the reflecting or comparison prism, the colored bands and the Fraun- 
hofer dark lines will appear directly continuous across the two spectra. 
The prism for the comparison spectrum is movable and may be entirely 
thrown out of the field if desired. When it is to be used, it is thrown 
about half way across the field so that the two spectrums shall have 
about the same width. 
§ 138. Scale of Wave Lengths.—In the Abbe micro-spectroscope 
the scale is in a separate tube near the top of the prism and at right angles 
to the prism-tube. A special mirror serves to light the scale, which is 
projected upon the spectrum by a lens in the scale-tube. This scale is 
of the Angstrom form, and the wave lengths of any part of the spec- 
trum may be read off directly, after the scale is once set in the proper 
position, that is, when it is set so that any given wave length on the 
scale is opposite the part of the spectrum known by previous investiga- 
tion to have that particular wave length. The point most often selected 
for setting the scale is opposite the sodium lines where the wave length 
is, according to Angstrom, 0.5892 fx. In adjusting the scale, one may 
focus very sharply the dark sodium line of the solar spectrum and set 
the scale so that the number 0.589 is opposite the sodium or D line, or 
a method that is frequently used and serves to illustrate § 129 C., is to 
sprinkle some salt of sodium (carbonate of sodium is good) in an alco- 
hol lamp flame and to examine, this flame. If this is done in a dark- 58 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
ened place with a spectroscope, two narrow bright yellow bands will be 
seen in the yellow part of the spectrum. If now ordinary daylight is sent 
through the comparison prism, the bright lines of the sodium will be 
seen to be directly continuous with the dark lines at D in the solar spec- 
trum (PI. V, Fig. 45). Now, by reflecting light into the scale-tube, 
the image of the scale will appear on the spectrum, and by a screw just 
under the scale-tube, but in the prism-tube,the proper point on the scale 
(0.589/x) can be brought opposite the sodium bands. All the scale 
will then give the wave lengths directly. Sometimes the scale is 
oblique to the spectrum. This may be remedied by turning the prism- 
tube slightly one way or the other. It may be due to the wrong posi- 
tion of the scale itself. If so, grasp the milled ring at the distal end of 
the scale-tube and, while looking into the spectroscope, rotate the tube 
until the lines of the scale are parallel with the Fraunhofer lines. It is 
necessary in adjusting the scale to be sure that the larger number 0.70 
is at the red end of the spectrum. 
The numbers on the scale should be very clearly defined. If they do 
not so appear, the scale-tube must be focused by grasping the outer tube 
of the scale-tube and moving it toward or from the prism-tube until the 
scale is distinct. In focusing the scale, grasp the outer scale-tube with 
one hand and the prism-tube with the other, and push or pull in opposite 
directions. In this way one will be less liable to injure the spectroscope. 
§ 139. Designation of Wave Length.—Wave lengths of light are 
designated by the Greek letter X, followed by the number indicating 
the wave length in some fraction of a meter. With the Abbe micro- 
spectroscope the micron is taken as the unit as with other .microscopical 
measurements (§ 108). Various units are in use, as the one hundred 
thousandth of a millimeter, millionths or ten millionths of a millimeter. 
If these smaller units are taken, the wave lengths will be indicated 
either as a decimal fraction of a millimeter or as whole numbers. 
Thus, according to Angstrom, the wave length of sodium light is 
5892 ten millionths mm. or 589.2 millionths, or 58.92 one hundred 
thousandths, or 0.5892 of one thousandth mm., or 0.5892/x. The last 
would be indicated thus, X D =0.5892 /x. 
§ 140. Lighting for the Micro-spectroscope.—For opaque objects a 
strong light should be thrown on them either with a concave mirror or a 
condensing lens. For transparent objects the amount of the substance 
and the depth of color must be considered. As a general rule it is well 
to use plenty of light, as that from an Abbe illuminator with a large 
opening in the diaphragm, or with the diaphragm entirely removed. 
For very small objects and thin layers of liquids it may be better to 
use less light. One must try both methods in a given case, and learn 
by experience. For many objects some good artificial light is better 
than daylight. 59 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
The direct and the comparison spectrums should be about equally il- 
luminated. One can manage this by putting the object requiring the 
greater amount of illumination on the stage of the microscope, and 
lighting it with the Abbe illuminator. 
§ 141. Objectives to Use with the Micro-spedtroscope.—If the 
material is of considerable bulk a low objective (18 to 50 mm.) is to be 
preferred. This depends on the nature of the object under examina- 
tion, however. In case of individual crystals one should use sufficient 
magnification to make the real image of the crystal entirely fill the 
width of the slit. The length of the slit may then be regulated by the 
screw on the side of the drum, and also by the comparison prism. If 
the object does not fill the whole slit the white light entering the spec- 
troscope with the light from the object might obscure the absorption 
bands. 
In using high objectives with the micro-spectroscope one must very 
carefully regulate the light (§§ 39, 68), and sometimes shade the object. 
§ 142. Focusing the Objective.—For focusing the objective the 
prism-tube is swung aside, and then the slit made wide by turn- 
ing the adjusting screw at the side. When the slit is open, one can see 
objects when the microscope is focused as with an ordinary ocular. 
After an object is focused, it may be put exactly in position to fill the 
slit of the spectroscope, then the knife edges are brought together till 
the slit is of the right width ; if the slit is then too long it may be 
shortened by using one of the mechanism screws on the side, or if that 
is not sufficient, by bringing the comparison prism farther over the 
field. If one now replaces the Amici prism and looks into the micro- 
scope, the spectrum is liable to have longitudinal shimmering lines. 
To get rid of these focus up or down a little so that the microscope 
will be slightly out of focus. 
§ 143. Amount of Material Necessary for Absorption Spectra 
and its Proper Manipulation.—The amount of material necessary to 
give an absorption spectrum varies greatly with different substances, 
and can be determined only by trial. If a transparent solid is under 
investigation it is well to have it in the form of a wedge, then succes- 
sive thicknesses can be brought under the microscope. If a liquid 
substance is being examined, a watch glass with sloping sides forms an 
excellent vessel to contain it, then successive thicknesses of the liquid 
can be brought into the field as with the wedge shaped-solid. Fre- 
quently only a very weak solution is obtainable, in this case it can be 
placed in a homoeopathic vial or in some glass tubing sealed at the end, 
then one can look lengthwise through the liquid and get the effect of a 
more concentrated solution. For minute bodies like crystals or blood 
corpuscles, one may proceed as described in the previous section. 60 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
MICRO-SPECTROSCOPE—EXPERIMENTS. 
§ 144- Put the micro-spectroscope in position, arrange the slit and 
the Amici prism so that the spectrum shall show the various spectral 
colors going directly across it (§§ 133-135) and carefully focus the slit. 
This may be done either by swinging the prism-tube aside and pro- 
ceeding as for the ocular micrometer (§ 114) or by moving the eye-lens 
of the ocular up and down while looking into the micro-spectro- 
scope until the dark lines of the solar spectrum are distinct. If they 
cannot be made distinct by focusing the slit, then the light is too feeble 
or the slit is too wide (§ 136). With the lever move the comparison 
prism across half the field so that the two spectra shall be of about 
equal width. 
§ 145. Absorption Spectrum of Permanganate of Potash.—Make 
a solution of permanganate of potash in water of such a strength that 
a stratum 3 or 4 mm. thick is transparent. Put this solution in a 
watch-glass with sloping sides, and put it under the microscope. Use 
a 50 mm. or 18 mm. objective and use the full opening of the illumina- 
tor. Light strongly. Look into the spectroscope and slowly move the 
watch-glass into the field. Note carefully the appearance with the 
thin stratum of liquid at the edge and then as it gradually thickens on 
moving the watch-glass still farther along. Count the absorption 
bands and note particularly the red and blue ends. Compare carefully 
with the comparison spectrum. 
§ 146. Absorption Spectrum of Blood.—Obtain blood from a re- 
cently killed animal, or flame a needle, and after it is cool prick the 
finger two or three times in a small area, then wind a handkerchief or 
a rubber tube around the base of the finger and squeeze the finger with 
the other hand. Some blood will ooze out of the pricks. Rinse this 
off in a watch-glass partly filled with water. Continue to add the 
blood until the water is quite red. Place the watch-glass of diluted 
blood under the microscope in place of the permanganate, using the 
same objective, etc. Note carefully the spectrum. It would be advan- 
tageous to determine the wave length opposite the center of the dark 
bands. This may be done easily by setting the scale properly as de- 
scribed in § 138. Make another preparation, but use a homoeopathic 
vial instead of a watch-glass. Cork the vial and lay it down upon the 
stage of the microscope. Observe the spectrum. It will be like that 
in the watch-glass. Remove the cork and look through the whole 
length of the vial. The bands will be very much darker and if the 
solution is thick enough only red and a little orange will appear. Re- 
insert the cork and incline the vial so that the light traverses a very 
thin layer then gradually elevate the vial and the effect of a thicker 61 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
and thicker layer may be seen. Note especially that the two charac- 
teristic bands unite and form one wide band as the stratum of liquid 
thickens. Compare with the following : 
Add to the vial of diluted blood a drop or two of ammonium sul- 
phide, such as is used for a reducing agent in chemical laboratories. 
Shake the bottle gently and then allow it to stand for ten or fifteen 
minutes. Examine it and the two bands will have been replaced by a 
single less clearly defined band in about the same position. The blood 
will also appear somewhat purple. Shake the vial vigorously and the 
color will change to the bright red of fresh blood. Examine it again 
with the spectroscope and the two bands will be visible. After five or 
ten minutes another examination will show but a single band. 
Incline the bottle so that a very thin stratum may be exam- 
ined. Note that the stratum of liquid must be considerably thicker to 
show the absorption band than was necessary to show the two bands 
in the first experiment. Furthermore, while the single band may be 
made quite black on thickening the stratum, in will not separate into 
two bands with a thinner stratum. In this experiment it is very in- 
structive to have a second vial of fresh, diluted blood, say that from 
the watch-glass, before the opening to the comparison prism. The 
two-banded spectrum will then be in position to be compared with the 
spectrum of the blood treated with the ammonium sulphide. 
The two banded spectrum is of oxy-haemoglobm or arterial blood, 
the single banded spectrum is of haemoglobin (sometimes called re- 
duced haemoglobin) or venous blood, that is the respiratory oxj’gen is 
present in the two banded spectrum but absent from the single banded 
spectrum. When the bottle was shaken the haemoglobin took up 
oxygen from the air and became oxy-haemoglobin, as occurs in the 
lungs, but soon the ammonium sulphide took away the respiratory 
oxygen thus reducing the oxy-haemoglobin to haemoglobin. This 
may be repeated many times. For further spectroscopic study of blood, 
see Part II. 
§ 147. Colored Bodies not giving Distinctly Banded Absorp- 
tion Spectra.—Some quite brilliantly colored objects, like the skin of 
a red apple, do not give a banded spectrum. Take the skin of a red 
apple, mount it on a slide, put on a cover-glass and add a drop of water 
at the edge of the cover. Put the preparation under the microscope 
and observe the spectrum. Although no bands will appear, in some 
cases at least, yet the ends of the spectrum will be restricted and vari- 
ous regions of the spectrum will not be so bright as the comparison 
spectrum. Here the red color arises from the mixture of the unab- 
sorbed wave lengths, as occurs with other colored objects. I11 this 
case, however, not all the light of a given wave length is absorbed, 62 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
consequently there are no clearly defined dark bands, the light is 
simply less brilliant in certain regions and the red rays so preponder- 
ate that they give the prevailing color. 
§ 148. Absorption Specftrum of Colored Minerals.—As example 
take some malazeit sand on a slide and either mount it in balsam (see 
§ 176), or cover and add a drop of water. The examination may be 
made also with the dry sand, but it is less satisfactory. Light well with 
transmitted light, and move the preparation slowly around. Absorp- 
tion bands will appear occasionally. Swing the prism-tube off the oc- 
ular, open the slit and focus the sand. Get the image of one or more 
grains directly in the slit, then narrow and shorten the slit so that no 
light can reach the spectroscope that has not traversed the grain of 
sand. The spectrum will be very satisfactory under such conditions. 
It is frequently of great service in determining the character of unknown 
mineral sands to compare their spectra with known minerals. If the 
absorption bands are identical, it is strong evidence in favor of the iden- 
tity of the minerals. 
REFERENCES TO THE MICRO-SPECTROSCOPE AND SPECTRUM ANALYSIS. 
\ 149. The micro-spectroscope is playing an ever increasingly important role in 
the spectrum analysis of animal and vegetable pigments, and of colored mineral 
and chemical substances, therefore a somewhat extended reference to literature 
will be given. Full titles of the books and periodicals will be found in the Bibli- 
ography at the end. 
Angstrom, Recherches sur le spectre solaire, etc. Also various papers in peri- 
odicals. See Royal Soc’s Cat’l Scientific Papers; Anthony & Brackett ; Beale, p. 
269; Behrens, p. 139 ; Behrens, Kossel und Schiefferdecker, p. 63 ; Carpenter p. 
104 ; Browning, How to Work with the Spectroscope, and in Monthly Micr. Jour., 
II, p. 65 ; Daniell, Principles of Physics. The general principles of spectrum 
analysis are especially well stated in this work, pp. 435-455 ; Dippel, p. 277 ; Frey ; 
Gamgee, p. 91 ; Halliburton ; Hogg, p. 122 ; also in Monthly Micr. Jour., Vol. II, 
on colors of flowers ; Jour. Roy. Micr. Soc., 1880, 1883 and in various other vols. ; 
Kraus ; Rockyer ; M’Kendrick ; Macmunn ; and also in Philos. Trans. R. S., 18S6 ; 
Various vols. of Jour. Physiol.; Nageli und Schwendener ; Proctor; Ref. Hand- 
Book Med. Sciences, Vol. I, p. 577, VI, p. 516, VII, p. 426 ; Roscoe ; Schellen ; 
Sorby, in Beale, p. 269, also Proc. R. S., 1874, p. 31, 1867, p. 433 ; see also in the 
Scientific Review, Vol. V, p. 66, Vol. II, p. 419. The larger works on Physiology, 
Chemistry and Physics may also be consulted with profit. 
MICRO-POLARISCOPE. 
§ 150. The micro-polariscope or polarizer is a polariscope used in connection 
with a microscope. 
The most common and typical form consists of two Nicol prisms, that is two 
somewhat elongated rhombs of Iceland spar cut obliquely and cemented together 
with Canada balsam. These Nicol prisms are then mounted in such a way that 63 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
the light passes through them lengthwise, and in passing is divided into two raj7s 
of plane polarized light. The one of these rays obeying most nearly the ordinary 
law of refraction is called the ordinary ray, the one departing farthest from the 
law is called the extra-ordinary ray. These two rays are not only polarized, but 
polarized in planes almost exactly at right angles to each other. The Nicol prism 
totally reflects the ordinary ray at the cemented surface so that only the extra- 
ordinary ray is transmitted. 
§ 151. Polarizer and Analyzer.—The polarizer is one of the Nicol prisms. It is 
placed beneath the object and in this way the object is illuminated with polarized 
light. The analyzer is the other Nicol and is placed at some level above the ob- 
ject, very conveniently above the ocular. 
When the corresponding faces of the polarizer and analyzer are parallel, i. e., 
when the faces through which the oblique section passed are parallel, light passes 
freely through the analyzer to the eye. If these corresponding faces are at right 
angles, that is if the Nicols are crossed, then the light is entirely cut off and the 
two transparent prisms become opaque to ordinary light. There are then, in the 
complete revolution of the analyzer, two points, at o° and at 1800, where the corre- 
sponding faces are parallel and where light freely traverses the analyzer. There 
are also two crossing points of the Nicols, at 90° and 270°, where the light is ex- 
tinguished. In the intermediate points there is a sort of twilight. 
\ 152. Putting the Polarizer and Analyzer in Position.—Swing the diaphragm 
carrier of the Abbe illuminator out from under the illuminator, remove the disk 
diaphragm or open widely the iris diaphragm and place the analyzer in the dia- 
phragm carrier, then swing it back under the illuminator. Remove the ocular, 
put the graduated ring on the top of the tube and then replace the ocular and put 
the analyzer over the ocular and ring. Arrange the graduated ring so that the in- 
dicator shall stand at o° when the field is lightest. This may be done by turning 
the tube down so that the objective is near the illuminator, then shading the stage 
so that none but polarized light shall enter the microscope. Rotate the analyzer 
until the lightest possible point is found, then rotate the graduated ring till the 
index stands at o°. The ring may then be clamped to the tube by the side screw 
for the purpose. 
\ 153. Adjustment of the Analyzer.—The analyzer should be capable of moving 
up and down in its mounting, so that it can be adjusted to the eye-point of the 
ocular with which it is used. If on looking into the analyzer with parallel Nicols 
the edge of the field is not sharp, or if it is colored, the analyzer is not in a 
proper position with reference to the eye-point and should be raised or lowered 
till the edge of the field is perfectly sharp and as free from color as the ocular 
with the analyzer removed. 
\ 154. Objectives to Use with the Polariscope.—Objectives of the lowest power 
may be used and also all intermediate forms up to a 2 mm. homogeneous immer- 
sion. Still higher Objectives may be used if desired. In general, however, the 
lower powers are somewhat more satisfactory. A good rule to follow in this case 
is the general rule in all microscopic work, “ use the power that most clearly and 
satisfactorily shows the object under investigation.'" 
§ 155. Lighting for Micro-Polariscopic Work.—Follow the general directions 
given in Chapter I. It is especially necessary to shade the object so that no un- 
polarized light can enter the objective, otherwise the field cannot be sufficiently 
darkened. No diaphragm is used over the polarizer for most examinations. Direct 
sunlight may be used to advantage with some objects, and as a rule the object 64 
MICRO-SPECTROSCOPE AND POLARISCOPE. 
would best be very transparent. That is, tissues, fibers, etc., should be mounted 
in balsam (Suffolk). 
| 156. Purpose of a Micro-Polariscope.—The object of a micro-polariscope is to 
determine, in microscopic masses, one or more of the following points: (A) 
Whether the body is singly refractive, mono-refriugent or isotropic, that is opti- 
cally homogeneous, as is glass and crystals belonging to the cubical system ; (B) 
Whether the object is doubly refractive, birefringent or anisotropic, uniaxial or bi- 
axial ; (C) Pleochromism ; (D) The rotation of the plane of polarization, as with 
solutions of sugar, etc. ; (E) To aid in petrology and mineralogy ; (F) To aid in 
the determination of very minute quantities of crystallizable substances ; (G) For 
the production of colors. 
For petrological and mineralogical investigations the stage of the microscope 
should possess a graduated rotating stage so that the object can be rotated and the 
exact angle of rotation determined. It is also found of advantage in investigating 
objects with polarized light where colors appear, to combine a polariscope and 
spectroscope (Spectro-Polariscope). 
MICRO-POEARISCOPE—EXPERIMENTS. 
§ 157- Arrange the polarizer and analyzer as directed above (§ 152) 
and use an 18 mm. objective except when otherwise directed. 
(A) Isotropic or Singly Refractive Objects.—Light the micro- 
scope well and cross the Nicols, shade the stage and make the field as 
dark as possible (§ 151). As an isotropic substance, put an ordinary 
glass slide under the microscope. The field will remain dark. As an 
example of a crystal belonging to the cubical system and hence iso- 
tropic, make a strong solution of common salt (sodium chloride Na Cl.), 
put a drop on a slide and allow it to crystallize, put it under the micro- 
scope, remove the analyzer, focus the crystals and then replace the an- 
alyzer and cross the Nicols- The field and the crystals will remain 
dark. 
(B) Anisotropic or Doubly Refracting Objects.—Make a fresh 
preparation of carbonate of lime crystals like that described for pedesis 
(§ 95), or use a preparation in which the crystals have dried to the 
slide, use a 5 or 3 mm. objective, shade the object well, remove the an- 
alyzer and focus the crystals, then replace the analyzer. Cross the 
Nicols. In the dark field will be seen multitudes of shining crystals, 
and if the preparation is a fresh one in water, part of the smaller crys- 
tals will alternately flash and disappear. By observing carefully, some 
of the larger crystals will be found to remain dark with crossed Nicols, oth- 
ers will shine continuously. This shows that the crystals are uniaxial. If 
the crystals are in such a position that the light passes through them par- 
allel with the principal axis, the oystals are isotropic like the salt crys- 
tal and remain dark. If, however, the light traverses them in any 
other direction the ray from the polarizer is divided into two constitu- 
ents vibrating in planes at right angles to each other, and one of these 65 
MICRO-SPECTROSCOPE AND POLARISCOPE: 
will traverse the analyzer, hence such crystals will appear as if self 
luminous in a dark field. The experiment with these crystals from the 
frog succeeds well with a 2 mm. homogeneous immersion. 
As further illustrations of anisotropic objects, mount some cotton 
fibers in balsam (Ch. V), also some of the Japanese paper (§ 72). 
These furnish excellent examples of vegetable fibers. 
Striated muscular fibers are also very well adapted for polarizing ob- 
jects. 
As examples of biaxial crystals, crystallize some borax, or carbonate 
of lead on a slide as directed for the common salt, and use the crystals 
as object. As all these objects restore the light with crossed Nicols, 
they are sometimes called depolarizing. 
(C) Pleochromism.—This is the exhibition of different tints as the 
analyzer is rotated. An excellent subject for this will be found in 
blood crystals (See Part II.). 
(D) For the aid given by the polariscope in micro chemistry, see 
Ch. V. 
(E) See works on petrology and mineralogy for the application of 
the micro-polarizer in those subjects. 
(F) For the production of gorgeous colors a plate of selenite giving 
blue and yellow colors is placed between the polarizer and the object. 
If properly mounted, the selenite is very conveniently placed on the 
diaphragm carrier of the Abbe illuminator, just above the polarizer. 
It is very instructive and interesting to examine' organic and inor- 
ganic substances with a micro-polarizer. If the objects enumerated in 
§ 96 were all examined with polarized light an additional means of de- 
tecting them would be found. 
REFERENCES TO THE POEARISCOPE AND TO THE USE OF POLARIZED 
LIGHT. 
Anthony & Brackett; Behrens, 133 ; Behrens, Kossel und Schiefferdecker ; Car 
noy, 61 ; Carpenter, 131, 839 ; Daniell, 494 ; v. Ebener ; Ganigee ; Halliburton, 36, 
272 ; Hogg, 133, 729 ; Lehmann ; M’Kendrick ; Nageli und Schwendeuer, 299 
Quekett; Suffolk, 125 ; Valentin. CHAPTER V. 
SLIDES AND COVER-GLASSES, MOUNTING, LABELING 
AND STORING MICROSCOPICAL PREPARATIONS—EX- 
PERIMENTS IN MICRO-CHEMISTRY. 
APPARATUS AND MATERIAL FOR THIS CHAPTER. 
Microscope, compound and simple (Ch. I); Micro-Spectroscope and polari- 
scope (Ck. IV); Slides and cover-glasses (§§ 158, 160); Cleaning mixtures for glass 
(§ 164) ; Alcohol and distilled or filtered water ($ 161) ; Fine forceps for handling 
cover-glasses (££ 161, 172) ; Old handkerchiefs or Japanese paper (§§ 72, 161) ; 
Paper boxes for storing cover-glasses i6r, 163) ; Cover-glass measurer ; Mount- 
ing material,—Farrant’s solution, glycerin, glycerin-jelly and Canada balsam 
(§£ 188-191); Centering card and lined card for serial sections ($ 172); Net-mi- 
crometer for arranging minute objects like diatoms (§ 195) ; Labels, ($ 194); Car- 
bon ink for writing labels ($ 182) ; Faber’s pencils for writing on glass, china, etc. 
(§ 186) ; Writing diamond ($ 182) ; Shellac cement (§$ 169, 193) ; Cabinet (§ 183); 
Reagents for experiments in micro-chemistry (£ 196). 
The laboratory furnishes all of the above articles except a simple microscope, 
slides and cover-glasses, fine forceps, handkerchiefs, paper boxes and Faber pen- 
cils. 
SLIDES AND COVER-GLASSES. 
§ 158. Slides, Glass Slides or Slips, Microscopic Slides or 
Slips.—These are strips of clear, flat glass upon which microscopic 
specimens are usually mounted for preservation and ready examina- 
tion. The size that has been almost universally adopted for ordinary 
preparations is 25x76 millimeters (1x3 inches). For rock sections, 
slides 25 x 45 mm. or 32 x 32 mm. are used ; for serial sections, slides 
50 x 75 mm. or 37 x 87 mm. are used. For special purposes, slides of 
the necessary size are employed without regard to any conventional 
standard. 
Whatever size of slide is used, it should be made of clear glass and 
the edges should be ground. It is altogether false economy to mount 
microscopic objects on slides with unground edges. 
§ 159. Cleaning Slides.—For new slides a thorough rinsing in clean 
water with subsequent wiping with a soft towel, and then an old soft 
handkerchief, usually fits them for ordinary use. If they are not satis- 
factorily cleaned in this way, soak them a short time in 50% or 75% 
alcohol, let them drain for a few moments on a clean towel or on blotting 
paper and then wipe with a soft cloth. In handling the slides grasp 
them by their edges to avoid soiling the face of the slide. After the EXPLANATION OF PLATE V. 
Fig, 41. Effect of the cover-glass on the ravs from the object to the objective 
(Ross). 
Axis. The projection of the optic axis of the microscope. 
F. Focus or axial point of the objective. 
F/ and F//. Points on the axis where rays 2 and 3 appear to originate if traced 
backward after emerging from the upper side of the cover-glass (cover). 
It is for the correction of this disturbance or so-called l< negative aberration ” 
produced by the cover-glass that objectives are fixed in their mounting for a given 
thickness of cover, or that the combinations making up the objective are made 
adjustable ; that is so that the back combinations may be brought nearer the front 
lens or combination as the cover thickens, and separated with a thinner cover or 
for uncovered objects. The thicker the cover, the nearer the front and back com- 
binations ; the thinner the cover the farther apart are front and back placed ($ 63). 
Fig. 42. Showing the course of the rays passing through a cover-glass from an 
axial point of the object, and the number that finally enter the front of a dry ob- 
jective. 
Fig. 43. Rays from the axial point of the object traversing a cover of the same 
thickness as in Fig. 42, and entering the front lens of a water immersion objective. 
Fig. 44. Rays from an axial point of the object traversing a cover-glass and en- 
tering the front of a homogeneous immersion objective. 
Figures 42-44, are somewhat modified from Ellenberger, and are introduced to 
illustrate the relative amount of utilized light, with dry, water immersion and 
homogeneous immersion objectives ($$ 9, 10, 18). 
Fig. 45. Absorption Spectrum of Oxy-Haemoglobin or arterial blood (1) and of 
Hcernoglobin or venous blood (2). (From Gamgee and MacMunn.) 
A, B, C, D, E, F, G, H. .Some of the principal Fraunhofer lines of the solar 
spect.um (2 129). 
.90, .80, .70, .60, .50, .40. Wave lengths in microns, as shown in Angstrom’s 
scale ($ 138). It will be seen that the wave lengths increase toward the red and de- 
crease toward the violet end of the spectrum. 
Red, Orange, Yellow, etc. Color regions of the spectrum. Indigo should come 
between the blue and the violet to complete the seven colors usually given. It 
was omitted through inadvertence. 
Fig. 46. Centering card to enable one easily to put objects in the center of a 
slide. It is made by drawing concentric circles in the center of a card and pasting 
pieces of board, or card board in the proper position to serve as guides to the slide. 
Fig. 47. Small spirit lamp modified into a balsam bottle or a glycerin or glycerin- 
jelly bottle. By adding a small brush, it answers well for a shellac bottle also. 
Fig. 48. Pipette for delivering drops or a small stream of any liquid. Made by 
tying sheet rubber over the top of a thistle bulb and connecting the bulb with a 
tapering ulass tube by a piece of rubber tube. 
Fig. 49. Glass slide with cover-glass, a drop of reagent and a bit of absorbent 
paper to show method of irrigation ($ 197). 
Fig. 50. Slide and cover-glass showing method of anchoring a cover-glass with a 
glycerin preparation when no cell is used. A cover-glass so anchored is not liable 
to move when the cover is being sealed ($ 169). 
Fig. 52-56. Various apparatus for the preparation of fibrin and for counting 
blood corpuscles, milk globules, etc. (These figures belong to Part II). 67 
MOUNTING AND LABELING. 
slides are cleaned, they should be stored in a place as free as possible 
from dust. 
For used slides, if only water, glycerin or glycerin jelly has been 
used on them, they may be cleaned with water, or preferably, warm 
water and then with alcohol if necessary. Where balsam or any oily 
or gummy substance has been used upon the slides they may be best 
freed from the balsam, etc., by soaking them for a week or more, in one 
of the cleaning mixtures for glass (§ 164). After «all foreign matter is 
removed the slides should be very thoroughly rinsed in water to remove 
all the cleaning mixture. They may then be treated as directed for 
new slides. 
§ 160. Cover-Glasses or Covering Glasses.—These are circular or 
quadrangular pieces of thin glass used for covering and protecting mi- 
croscopic objects. They should be very thin, to millimeter 
(see table, § 17). It is better never to use a cover glass over y mm. 
thick then the preparation may be studied with a 2 mm. oil immersion 
as well as with lower objectives. Except for objects wholly unsuited 
for high powers, it is a great mistake to use cover-glasses thicker than 
the working distance of a homogeneous objective (§ 38). 
The cover-glass should always be considerably larger than the object 
over which it is placed. 
§ 161. Cleaning Cover-Glasses.—New cover-glasses should be put 
into a glass dish of some kind containing one of the cleaning mix- 
tures (§ 164) and allowed to remain a day or longer. In putting them in, 
push one in at a time and be sure that it is entirely immersed, otherwise 
they adhere very closely, and the cleaning mixture is unable to act 
freely. Soiled covers should be left a week or more in the cleaning 
mixture. An indefinite sojourn in the cleaner does not seem to injure 
the slides or covers. After one day or longer, pour off the cleaning 
mixture into another glass jar, and rinse the cover glasses, moving them 
around with a gentle rotary motion. Continue the rinsing until all the 
cleaning mixture is removed. One may rinse them occasionally, and 
in the meantime allow a very gentle stream of water to flow on them or 
they may be allowed to stand quietly and have the water renewed from 
time to time. When the cleaning mixture is removed rinse the covers 
well with distilled water, and then cover them with 50% to 75 % alcohol. 
Wiping the cover-glasses.—When ready to wipe the cover-glasses re- 
move several from the alcohol and put them on a soft dry cloth or on 
some of the Japanese paper, to let them drain. Grasp a cover-glass by 
its edges, cover the thumb and index of the other hand with a soft 
clean cloth or some of the Japanese paper. Grasp the cover between 
the thumb and index and rub the surfaces. In doing this it is neces- 
sary to keep the thumb and index well opposed of on directly opposite 68 
MOUNTING AND LABELING. 
faces of the cover so that no strain will come on it, otherwise the cover 
is liable to be broken. 
When a cover is well wiped, hold it up and look through it toward 
some dark object. The cover will be seen partly by transmitted and 
partly by reflected light, and any cloudiness will be easily seen. If the 
cover does not look clear, breathe on the faces and wipe again. If it is 
not possible to get a cover clear in this way it should be put again into 
the cleaning mixture. 
As the covers are wiped put them in a clean paper box. Handle 
them always by their edges, or use fine forceps. Do not put the fingers 
on the faces of the covers, for that will surely cloud them. 
§ 162. Cleaning Large Cover-Glasses.—For serial sections and 
especially large sections, large quadrangular covers are used. These 
are to be put one by one into cleaning mixture as for the smaller covers 
and treated in every way the same. In wiping them one may proceed 
as for the small covers, but special care is necessary to avoid breaking 
them. A safe and good way to clean the large covers is to take two 
perfectly flat, smooth blocks considerably larger than the cover- 
glasses. These blocks are covered with soft clean cloth, or with sev- 
eral thicknesses of the Japanese paper ; if now the cover-glass is placed 
on the one block and rubbed with the other the cover may be cleaned 
as by rubbing its faces with the cloth covered finger and thumb. 
§ 163. Measuring the Thickness of Cover-Glasses.—It is of the 
greatest advantage to know the exact thickness of the cover-glass on an 
object; for, (a) One would not try to use objectives in studying the 
preparation of a shorter working distance than the thickness of the 
cover (§ 38) ; (b) In using adjustable objectives with the collar gradu- 
ated for different thicknesses of cover, the collar might be set at a 
favorable point without loss of time ; (c) For unadjustable objectives 
the thickness of cover may be selected corresponding to that for which 
the objective was corrected 9 (see table § 17). Furthermore, if there 
is a variation from the standard, one may remedy it, in part at least, 
by lengthening the tube if the cover is thinner, and shortening it if 
the cover is thicker than the standard (§ 63). 
In the so called No. 1 cover-glasses of the dealers in microsopical 
supplies, the writer has found covers varying from TYV 111m. to T3<f0 
mm. To use cover-glasses of so wide a variation in thickness without 
knowing whether one has a thick or a thin one is simply to ignore the 
fundamental principles on which correct microscopic images are ob- 
tained. 
It is then strongly recommended that every preparation shall be cov- 
ered with a cover-glass whose thickness is known, and that this thick- 
ness should be indicated in some way on the preparation. 69 
MOUNTING AND LABELING. 
For the purpose of measuring cover-glasses two very convenient 
cover-glass measures or cover-glass testers have been devised, one made 
and furnished by Zeiss, Reichert, etc., in Europe, and the other, de- 
vised by Edward Bausch and furnished by the Bausch and Eomb Opti- 
cal Co. of Rochester, N. Y. With either of these the cleaned covers 
may be very quickly and accurately measured. The different thick- 
nesses can then be put into different boxes and properly labeled. 
Unless one is striving for the most accurate possible results, cover- 
glasses not varying more than yjy mm. may be put in the same box. 
For example, if one takes mm. as a standard, covers' varying T-|y 
mm. on each side may be put into the same box. In this case the box 
would contain covers of TW, TV\, TVV> tW and xVd mm. 
Fig. 38. Cover-Glass Measurer (.Edward Bausch). 
The cover-glass is placed in the notch between the two screws, and the 
drum is turnea by the milled head at the right till the cover is in contact 
with the screws. The thickness is then indicated by the knife edge on the 
drum, and may be read off directly in jffth mm. or jxnroth inch. In 
other columns is given the proper tube-length for various unadjustable ob- 
jectives (y, i, and Ty, in.) made by the Bausch and Lomb Optical Co. 70 
MOUNTING AND LABELING. 
§ 164. Cleaning Mixtures for Glass.—The cleaning mixtures used 
for cleaning slides and cover-glasses are those commonly used in chem- 
ical laboratories : 
(A) Dichromate of Potash and Sulphuric Acid. 
Dichromate of potash (K2 Cr2 07) 200 grams. 
. Water, distilled or ordinary 1000 cc. 
Sulphuric acid (H2 S04) 1000 cc. 
Dissolve the dichromate in the water by the aid of heat. Pour the 
solution into a bottle that has been warmed. Add slowly and at inter- 
vals the sulphuric acid. 
For making this mixture, ordinary water, commercial dichromate 
and strong commercial sulphuric acid should be used. It is not neces- 
sary to employ chemically pure materials. 
This is a very excellent cleaning mixture and is practically odorless. 
It is exceedingly corrosive and must be kept in glass vessels. It may 
be used more than once, but when the color changes markedly from 
that seen in the fresh mixture it should be thrown away. 
(B) Sulphuric and Nitric Acid Mixture. 
Nitric acid (H NOs) 200 cc. 
Sulphuric acid (H2 S04) 300 cc. 
The acids should be strong, but they need not be chemically pure. 
The two acids are mixed slowly, and kept in a glass-stoppered bottle. 
This is a more corrosive mixture than (A) and has the undesirable fea- 
ture of giving off very stifling fumes, therefore it must be carefully 
covered. It may be used several times. It acts more rapidly than the 
dichromate mixture but on account of the fumes is not so well adapted 
for general laboratories. 
MOUNTING, AND PERMANENT PREPARATION OF MICROSCOPICAL 
OBJECTS. 
§ 165. Mounting a microscopical object is so arranging it upon 
some suitable support (glass slide) and in some suitable mounting 
medium that it may be satisfactorily studied with the microscope. 
Some objects are mounted dry or in air, others in some liquid misci- 
ble with water, as glycerin, and still others in some resinous medium 
like Canada balsam. Special methods of procedure are necessary in 
order to mount objects successfully in each of these ways. The best 
mounting medium and the best method of mounting in a given case 
can only be determined by experiment, unless some previous observer 
has already supplied the information. 
The cover-glass on a permanent preparation should always be consider- 
ably larger than the object; and where several objects are put under one 
cover-glass it is false economy to crowd them too closely together. 71 
MOUNTING AND LABELING. 
§ 166. Mounting Cells.—Many objects are of considerable thickness 
and require a space or cell in which to be mounted, the wall of the cell 
serving to support the cover-glass and to contain the mounting medium. 
Where objects are mounted dry, that is in air, a cell must always be 
used to support the cover-glass and to prevent the soft cement used in 
sealing the preparation from running in by capillarity and thus flooding 
the preparation. 
Fig. 2)8a. Turn-Table for Sealing Cover- Glasses and Making 
Shallow Mounting Cells. (Queen & Co.) 
§167. Preparation of Mounting Cells.—(A) Thin Cells. These are 
most conveniently made of some of the microscopical cements. Shellac 
is one of the best and most generally applicable (§ 193). To prepare a 
shellac cell, place the slide on a turn-table (Fig. 38a) and center it, that 
is get the center of the slide over the center of the turn-table. Select a 
guide ring on the turn-table which is a little smaller than the cover- 
glass to be used, take the brush from the shellac, being sure there is 
not enough cement adhering to it to drop. Whirl the turn-table and 
hold the brush lightly on the slide just over the guide ring selected. 
An even ring of the cement should result. If it is uneven, the cement 
is too thick or too thin or too much was on the brush. After a ring is 
thus prepared remove the slide and allow the cement to dry spontan- 
eously or heat the slide in some way. Before the slide is used for 
mounting, the cement should be so dry when it is cold that it does not 
dent with the finger nail applied to it. 
A cell of considerable depth may be made with the shellac by adding 
successive layers as the previous one drys. 
(B) Deep cells are sometimes made by building up cement cells, but 
more frequently, paper, wax, glass, hard rubber or some metal is used 
for the main part of the cell; Paper rings, block tin or lead rings are 
easily cut out with gun punches. These rings are fastened to the 
slide by using some cement like the shellac. 
§ 168. Sealing the Cover-Glass.—(A) For dry objects mounted in 
cells. When an object is mounted in a cell, the slide is warmed until 
the cement is slightly sticky, or a very thin coat of fresh cement is put 72 
MOUNTING AND LABELING. 
on. The cover-glass is warmed slightly also, both to make it stick to 
the cell more easily, and to expel any remaining moisture from the ob- 
ject. When the cover is put on it is pressed down all around over the 
cell until a shining ring appears, showing that there is an intimate con- 
tact. In doing this use the convex part of the fine forceps or some 
other blunt, smooth object; it is also necessary to avoid pressing on the 
cover except immediately over the wall of the cell for fear of breaking 
the cover. When the cover is in contact with the wall of cement all 
around, the slide should be placed on the turn-table and carefully ar- 
ranged so that the cover-glass and cell wall will be concentric with the 
guide rings of the turn-table. Then the turn-table is whirled and a 
ring of fresh cement is painted, half on the cover and half on the cell 
wall (Fig. 40). If the cover-glass is not in contact with the cell wall at 
any point and the cell is shallow, there will be great danger of the fresh 
cement running into the cell and injuring or spoiling the preparation. 
When the cover-glass is properly sealed, the preparation is put in some 
safe place for the drying of the cement. It is advisable to add a fresh 
coat of cement occasionally. 
(B) Thick or deep cells. These may be made of paper, sheet lead or 
block tin, etc. They should be slightly deeper than the object to be 
mounted is thick. It is sometimes advisable to have a circular opening 
and an oblong wall instead of using a mere ring. In any case the cell 
wall is cemented to the slide and the cement well dried before use. If 
the cell is for dry objects or for those in glycerin, a ring of fresh cement 
is added just before putting on the cover-glass. If glycerin jelly, a res- 
inous substance, or Farrant’s solution is to be used as the mounting 
medium no cement on the top is necessary. 
§ 169. Sealing the Cover-Glass when no Cell is Used.—(A) 
For glycerin mowited specimens. The superfluous glycerin is wiped 
away as carefully as possible with a moist cloth, then four minute drops 
of cement are placed at the edge of the cover (PI. V, Fig. 50), and 
allowed to harden for half an hour or more. These will anchor the 
cover-glass, then the preparation may be put on the turn-table and a ring 
of cement put around the edge while whirling the turn-table. 
(B) For objects in glycerin jelly, Farrant's solution or a resinous me- 
dium. The mounting medium is first allowed to harden, then the su- 
perfluous medium is scraped away as much as possible with a knife, and 
then removed with a cloth moistened with water for the glycerin jelly 
and Farrant’s solution or with alcohol, chloroform or turpentine, etc., 
if a resinous medium is used. Then the slide is put on a turn-table and 
a ring of the shellac cement added. (C) Balsam preparations may be 
sealed with shellac as soon as they are prepared, but it is better to al- 
low them to dry for a few days. One should never use a cement for 73 
MOUNTING AND LABELING. 
sealing preparations in balsam or other resinous media unless the solvent 
of the cement is not a solvent of the balsam, etc. Otherwise the ce- 
ment will soften the balsam and finally run in and mix with it, and 
partly or wholly ruin the preparation. Shellac is an excellent cement 
for sealing balsam preparations, as it never runs in, and it serves to 
avoid any injury to the preparation when cedar oil, etc., are used for ho- 
mogeneous immersion objectives. 
§ 170. Order of Procedure in Mounting Objects Dry or in Air. 
1. A cell of some kind is prepared. It should be slightly deeper 
than the object is thick (§§ 166, 167). 
2. The object is thoroughly dried (desiccated) either in dry air or by 
the aid of gentle heat. 
3. If practicable the object is mounted on the cover-glass, if not it is 
placed in the bottom of the cell. 
4. The slide is warmed till the cement forming the cell wall is some- 
what sticky, or a thin coat of fresh cement is added ; the cover is 
warmed and put on the cell and pressed down all around till a shining 
ring indicates its adherence (§ 168). 
5. The cover-glass is sealed (§ 168). 
6. The slide is labeled (§ 179). 
7. The preparation is cataloged and safely stored (§§ 181-183). 
MOUNTING OF OBJECTS IN MEDIA MISCIBEE WITH WATER. 
§171. Many objects are so greatly modified by drying that they must 
be mounted in some medium other than air. In some cases water 
or water with something in solution is used. Glycerin of various 
strengths, glycerin jelly and Farrant’s solution are also much em- 
ployed (§§ 189, 190). All these media keep the object moist and there- 
fore in a condition resembling the natural one. The object is usually 
and properly treated with gradually increasing strengths of gly- 
cerin or fixed by some fixing agent (See Part II) before being perma- 
nently mounted in strong glycerin or either of the other media. 
In all of these different methods, unless glycerin of increasing 
strengths has been used to prepare the tissue, the fixing agent is 
washed away with water before the object is finally and permanently 
mounted in either of the media. 
For glycerin jelly or Farrant’s solution no cell is necessary unless the 
object has a considerable thickness. 
§ 172. Order of Procedure in Mounting Objects in Glycerin. 
1. A cell is employed if the object is of considerable thickness. 
2. The suitably prepared object (§ 171) is placed on the center of a 74 
MOUNTING AND L 4BELING. 
clean slide, and if no cell is required a centering card is employed to 
facilitate the centering (PI. V, Fig. 46). 
3. A drop of pure glycerin is put upon the object, or if a cell is used, 
enough to fill the cell. 
4. In putting on the cover-glass it is grasped with fine forceps and 
the under side breathed on to slightly moisten it so that the glycerin 
will adhere, then one edge of the cover is put on the cell or slide and 
the cover gradually lowered upon the object (PI. II, Fig. 14). The 
cover is then gently pressed down. If a cell is used, a fresh coat of ce- 
ment is added before mounting (§ 168 B). 
5. The cover-glass is sealed (§§ 168, 169). 
6. The slide is labeled (§ 179). 
7. The preparation is cataloged and safely stored (§§ 181-183). 
§ 173. Order of Procedure in Mounting Objects in Farrant’s 
Solution. 
A cell is only necessary when the object is of considerable thickness. 
The object may be considerably thicker than when glycerin is used 
without requiring a cell. 
1. The centering card is used (PI. V, Fig. 46), and a small drop 
of Farrant’s solution put in the middle. The suitably prepared ob- 
ject is then put on the solution in the center and carefully arranged as 
desired. 
2. A drop of the Farrant’s solution is put on the object, or if a cell is 
used it is filled with the medium. 
3. The cover-glass is grasped with fine forceps, the lower side 
breathed upon and then it is gradually lowered upon the object (PI. II, 
Fig. 14), and slightly pressed down. 
4. After the mounting medium has hardened round the edge of the 
cover-glass the superfluous medium is scraped and wiped away and the 
cover sealed with shellac (§§ 168, 169). 
5. The slide is labeled (§ 179). 
6. The preparation is cataloged and safely stored (§§ 181-183). 
§ 174. Order of Procedure in Mounting Objects in Glycerin 
Jelly. 
1. Unless the object is quite thick no cell is necessary with glycerin 
jelly. 
2. A slide is gently warmed and placed on the centering card 
(PI. V, Fig. 46) and a drop of warmed glycerin jelly is put on its cen- 
ter. The suitably prepared object is then arranged in the center of the 
slide. 
3. A drop of the warm glycerin jelly is then put on the object, or if a 
cell is used it is filled with the medium. 75 
MOUNTING AND LABELING. 
4. The cover-glass is grasped with fine forceps, the lower side 
breathed on and then gradually lowered upon the object (PI. II, Fig. 14), 
and gently pressed down. 
5. After mounting, the preparation is left flat in some cool place till 
the glycerin jelly sets, then the superfluous amount is scraped and wiped 
away and the cover-glass sealed with shellac (§§ 168, 169). 
6. The slide is labeled (§ 179). 
7. The preparation is cataloged and safely stored (§§ 181-183). 
MOUNTING OBJECTS IN RESINOUS MEDIA. 
§ 175- While the media miscible with water offer many advantages 
for mounting animal and vegetable tissues the preparations so made 
are liable to deteriorate. In many cases, also, they do not produce 
sufficient transparency to enable one to use sufficiently high powers for 
the demonstration of minute details. 
By using sufficient care almost any tissue may be mounted in a resin- 
ous medium and retain all its details of structure. 
For the successful mounting of an object in a resinous medium it 
must in some way be deprived of all water and all liquids not miscible 
with the resinous mounting medium. There are two methods of bring- 
ing this about: 
(A) By drying or desiccation. This answers well for many objects, 
for example, a fly’s wing, crystals, etc. 
(B) By a series of displacements. The first step in the series is 
Dehydration, that is the water is displaced by some liquid which is mis- 
cible both with the water and the next liquid to be used. Strong alco- 
hol (95% or stronger) is usually employed for this. Plenty of it must 
be used to displace the last trace of water. The tissue may be soaked 
in a dish of the alcohol, or alcohol from a pipette may be poured upon 
it. Dehydration usually occurs in the thin objects to be mounted in 
balsam in 5 to 15 minutes. If a dish of alcohol is used it must not be 
used too many times, as it loses its strength. 
The second step is clearing. That is some liquid which is miscible 
with the alcohol and also with the resinous medium is used. This 
liquid is highly refractive in most cases and consequently this step is 
called clearing and the liquid a Clearer. The clearer displaces the 
alcohol, and renders the object more or less translucent. I11 case the 
water was not all removed a cloudiness will appear in parts or over the 
whole of the preparation. In this case the preparation must be re- 
turned to alcohol to complete the dehydration. 
One can tell when a specimen is properly cleared by holding it over 
some dark object. If it is cleared it can be seen only with difficulty, as 76 
MOUNTING AND LABELING. 
but little light is reflected from it. If it is held toward the window, 
however, it will appear translucent. 
The third and final step is the displacement of the clearer by the 
resinous mounting medium. 
The specimen is drained of clearer and allowed to stand for a short 
time till there appears the first sign of dullness from evaporation of the 
clearer from the surface. Then a drop of the resinous medium is put 
on the object and finally a cover-glass is placed over it, or a drop of the 
mounting medium is spread on the cover and it is then put on the 
object. 
It is in many ways more convenient to perform the series of displace- 
ments on the slide. This must be done with serial sections. If the 
preparations are not fastened to the slide, some workers perform the 
dehydration and clearing in separate dishes. 
§ 176. Order of Procedure in Mounting Objects in Resinous 
Media by Desiccation. 
1. The object suitable for the purpose (fly’s wing, etc.) is thoroughly 
dried in dry air or by gentle heat. 
2. The object is arranged as desired in the center of a clean slide on 
the centering card (PI. V., Fig. 46.) 
3. A drop of the mounting medium (§ 191) is put directly upon the 
object or spread on a cover-glass. 
4. The cover-glass is put on the specimen with fine forceps (PI. II, 
Fig. 14), but in no case does one breathe on the cover as when media 
miscible water are used. 
5. The cover-glass is pressed down gently. 
6. The slide is labeled (§ 179). 
7. The preparation is cataloged and safely stored (§§ 181-183). 
8. Although it is not absolutely necessary, it is better to seal the 
cover with shellac after the medium has hardened round the edge of 
the cover (§ 169 C). 
§ 177. Order of Procedure in Mounting Objects in Resinous 
Media by successive Displacements. 
1. A suitable object is selected, for example a section of animal tis- 
sue, and is centered on a clean slide. 
2. The slide is held in the hand and the object is dehydrated by 
dropping upon it strong alcohol (§ 175 B). 
3. The alcohol is drained from the specimen and removed by blotting 
paper held at the edge of the object. 
4. Two or three drops of the clearer (§ 192) are put on the object to 
displace the alcohol (§ 175 B). 77 
MOUNTING AND LABELING. 
5. When the object appears translucent the clearer is drained off and 
blotted from the edge of the specimen (§ 175). 
6. A drop of the resinous medium is put directly on the object or 
spread upon a cover-glass. 
7. The cover-glass is put upon the object and pressed down. It may 
then be heated gently. 
8. The slide is labeled (§ 179). 
9. The preparation is cataloged and safely stored (§§ 181-183). 
10. After the resin has hardened round the edge of the cover the su- 
perfluous material may be cleaned away and the cover-glass sealed with 
shellac. This is not absolutely necessary, but is desirable (§ 169 C). 
LABELING, CATALOGING AND STORING MICROSCOPICAL PREPARA- 
TIONS. 
$ 178 Every person possessing a microscopical preparation is interested in its 
proper management; but it is especially to the teacher and the investigator that 
the labeling, cataloging and storing of microscopical preparations are of im- 
portance. “To the investigator, his specimens are the most precious of his pos- 
sessions, for they contain the facts which he tries to interpret, and they remain 
the same while his knowledge, and hence his power of interpretation, increase. 
They thus form the basis of further or more correct knowledge ; but in order to 
be safe-guides for the student, teacher, or investigator, it seems to the writer that 
every preparation should possess two things; viz., a label and a catalog or his- 
tory. This catalog should indicate all that is known of a specimen at the time 
of its preparation, and all of the processes by which it is treated. It is only by 
the possession of such a complete knowledge of the entire history of a prepara- 
tion that one is able to judge with certainty of the comparative excellence of 
methods, and thus to discard or improve those which are defective. The teacher, 
as well as the investigator, should have this information in an accessible form, so 
that not only he but his students can obtain at any time all necessary information 
concerning the preparations which serve him as illustrations and them as ex- 
amples.” 
$ 179. Labeling Ordinary Microscopical Preparations.—The label ($ 191) should 
possess at least the following information :— 
EXAMPLE. 
(1) The number of the preparation. 
(2) The thickness of the cover-glass. 
(3) The name and source of the prepara- 
tion. 
(4) The date on which the preparation 
is made. 
; NO. 475. 
j Cover-Glass, .15 mm. 
! Striated Muscular Fibers, Sartorius of 
Cat. 
October 1, 1891. 78 
MOUNTING AND LABELING. 
76 84 92 
77 85 93 
78 86 94 
79 ' 87 95 
80 88 96 
81 89 97 
82 90 98 
83 91 99 
Ser. No. 5 Cover 15 mm. 
Slide No. 4. 
Oral Epithelium of Diemyctylus. 
Sections 76-99. 
Total thickness 1 mm. 
Oct. i, 1891. 
Fig. 57.—Example of a slide of serial sections 
labeled for the cabinet. 
| 180. Arranging and Labeling Serial 
Sections.—In order to determine the mor- 
phological arrangement of embryos and 
minute animals where gross dissection is 
impossible, it has been found of the highest 
advantage to make serial sections. These, 
for convenience of study, should be placed 
on the slide with the dorsal side pointing 
toward the top of the slide (i. e., away from 
the label). The sections should all be the 
same side up also. If they are put with the 
caudal aspect up, then the dorsal side being 
toward the top of the slide, the various 
parts of the embryo or animal will have its 
right and left corresponding with the ob- 
server. Finally it is almost universally 
agreed that the sections shall be placed on 
the slide like columns of figures. 
In histological studies it is also frequently 
of great advantage to have the sections in 
serial order, then an obscure feature in one 
section is frequently made clear by the one following. It is only in the study of 
the individual, isolated, histological elements that serial sections are not uecessary 
or at least desirable. 
The label of a slide with serial sections should possess at least the following : 
1. The number of the series. 
2. The thickness of the cover-glass. 
3. The number of the slide in the series. 
4. The name and source of the series. 
5. The number of the first and last section on the slide. 
6. The total thickness of all the sections on the slide.* 
7. The date of making the preparation. 
§ 181. Cataloging Preparations.—It is believed from personal experience and 
from the experience of others, that each preparation should be accompanied by a 
catalog containing at least the following information. Of course when not ap- 
plicable any of the numbers in the formula may be suppressed, or the order 
changed: 
* The thickness of all the sections on a slide is easily determined by noting 
carefully the position of the microtome screw before the first and after the last 
section for the slide is cut. One can easily measure the amount of elevation of 
the screw in cutting the sections on a slide, and if the sections are of even thick- 
ness, the thickness of each section may be determined. The average thickness 
can be determined in any case. 79 
MOUNTING AND LABELING. 
General Formula for Cataloging Mi- 
croscopical Preparations : 
1. The general name and source. 
2. The number and date of the pre- 
paration and the name of the preparator. 
3. The special name of the prepara- 
tion and the common and scientific 
name of the object from which it is de- 
rived. 
4. The age and condition of the object 
from which the preparation is derived. 
5. The chemical treatment,—the 
method of fixing, hardening, dissociat- 
ing, etc. 
6. The mechanical treatment,—im- 
bedded, sectioned, dissected with nee- 
dles, etc. 
7. The staining agent and the time re- 
quired for staining. 
8. Dehydrating and clearing agent, 
mounting medium, cement used for 
sealing. 
9. The objectives and other accesso- 
ries (micro-spectroscope, polarizer, etc.) 
for studying the preparation. 
xo. Remarks, including references to 
original papers, or to good figures and 
descriptions in books. 
A Catalog Card Written According to 
this Formula : 
1. Striated Muscular Fibers. Cat. 
2. No. 475, (Drr. IX) Oct. i, 1891. S. 
H. G., Preparator. 
3. Tendinous and intra-muscular ter- 
minations of striated muscular fibers 
from the Sartorius of the cat (Felts do- 
mes tica). 
4. Cat eight months old, healthy and 
well nourished. 
5. Muscle pinned on cork with vas- 
elined pins and placed in 20 per cent, 
nitric acid immediately after death by 
chloroform. Left 36 hours ; tempera- 
ture 200 C. In alum water (sat. aq. sol.) 
1 day. 
6. Fibers separated on the slide with 
needles. 
7. Stained 5 minutes with Delafield’s 
haematoxylin. 
8. Mounted in glycerin jelly (§ 174). 
9. Use 18 mm. for the general appear- 
ance of the fibers, then 2 or 3 mm. ob- 
jective for the details of structure ($ 75). 
Try the micro-polariscope (f 157). 
10. The nuclei or muscle corpuscles 
are very large and numerous ; many of 
the intra-muscular ends are branched. 
See S. P. Gage, Proc. Amer. Micr. Soc., 
1890, p. 132 ; Ref. Haud-Bk. Med. Sci., 
Vol. V., p. 59. 
\ 182. General Remarks on Catalogs and Labels.—It is especially desirable 
that labels and catalogs shall be written with some imperishable ink. Some 
form of water-proof carbon ink is the most available and satisfactory. The water- 
proof India ink, or the engrossing carbon ink of Higgins, answers very well. 
As purchased the last is too thick for ordinary writing and should be diluted with 
one third its volume of water and a few drops of strong ammonia added. 
If one has a writing diamond it is a good plan to write a label with it on one end 
of the slide. It is best to have the paper label also, as it can be more easily read. 
The author has found stiff cards, postal card size like those used for cataloging 
books in public libraries, the most desirable form of catalog. A specimen that 
is for any cause discarded has its catalog card destroyed. New cards may then 
be added in alphabetical order as the preparations are made. In fact a catalog 
on cards has all the flexibility and advantages of the slip system of notes (see 
Wilder & Gage, p. 45). [From page 79 of the Microscope and Histology, Part I.] 
\ 181. Cataloging Preparations.—It is believed from personal experience and 
from the experience of others, that each preparation should be accompanied by a 
catalog containing at least the following information. Of course when not ap- 
plicable any of the numbers in the formula may be suppressed, or the order 
changed: 
General Formula for Cataloging Mi- 
croscopical Preparations : 
1. The general name and source. 
2. The number and date of the pre- 
paration and the name of the preparator. 
3. The special name of the prepara- 
tion and the common and scientific 
name of the object from which it is de- 
rived. 
4. The age and condition of the object 
from which the preparation is derived. 
5. The chemical treatment,—the 
method of fixing, hardening, dissociat- 
ing, etc. 
6. The mechanical treatment, — im- 
bedded, sectioned, dissected with nee- 
dles, etc. 
7. The staining agent and the time re- 
quired for staining. 
8. Dehydrating and clearing agent, 
mounting medium, cement used for 
sealing. 
9. The objectives and other accesso- 
ries (micro-spectroscope, polarizer, etc.) 
for studying the preparation. 
10. Remarks, including references to 
original papers, or to good figures and 
descriptions in books. 
A Catalog Card Written According to 
this Formula : 
1. Striated Muscular Fibers. Cat. 
2. No. 475, (Drr. IX) Oct. 1, 1891. S. 
H. G., Preparator. 
3. Tendinous and intra-muscular ter- 
minations of striated muscular fibers 
from the Sartorius of the cat (Felis do- 
mestica). 
4. Cat eight months old, healthy and 
well nourished. 
5. Muscle pinned on cork with vas- 
elined pins and placed in 20 per cent, 
nitric acid immediately after death by 
chloroform. Left 36 hours ; tempera- 
ture 200 C. In alum water (sat. aq. sol.) 
1 day. 
6. Fibers separated on the slide with 
needles. 
7. Stained 5 minutes with Delafield’s 
haematoxylin. 
8. Mounted in glycerin jelly ($ 174). 
9. Use 18 mm. for the general appear- 
ance of the fibers, then 2 or 3 mm. ob- 
jective for the details of structure ($ 75). 
Try the micro-polariscope ($ 157). 
10. The nuclei or muscle corpuscles 
are very large and numerous ; many of 
the intra-muscular ends are branched. 
See S. P. Gage, Proc. Amer. Micr. Soc., 
1890, p. 132 ; Ref. Hand-Bk. Med. Sci., 
Vol. V., p. 59- 
LABEL WITH EXAMPLE. 
(1) The number of the preparation. 
(2) The thickness of the cover-glass. 
(3) The name and source of the prepara- 
tion. 
(4) The date on which the preparation 
is made. 
No. 475. Cover-Glass, .15 mm. 
Striated Muscular Fibers, Sartorius of 
Cat. 
October 1, 1891. 80 
MOUNTING AND LABELING. 
Some workers prefer a book catalog. Very excellent book catalogs have 
been devised by Ailing and by Ward (Jour. Roy. Micr. Soc., 1887, pp. 173, 348 ; 
Amer. Monthly Micr. Jour., 1890, p. 91 ; Anier. Micr. Soc. Proc., 1887, p. 233). 
The fourth section in the cataloging formula has been introduced, as there is 
coming to be a belief that the tissues of young and of old animals differ in respect 
to the size of the nuclei (see Minot in Proc. Amer. Assoc. Adv. of Science, 1890, pp. 
271-289). It is also extremely desirable to know whether the animal is well or 
ill nourished, healthy or diseased. 
CABINET FOR MICROSCOPICAL PREPARATIONS. 
(5 183. While it is desirable that microscopical preparations should be properly 
labeled and cataloged, it is equally important that they should be protected from 
injury. During the last few years several forms of cabinets or slide holders have 
been devised. Some are very cheap and convenient where one has but a few 
slides. For a laboratory or for a private collection w7here the slides are numerous 
the following characters seem to the writer essential : 
(1) The cabinet should allow7 the slides to lie flat, and exclude dust and light. 
(2) Each slide or pair of slides should be in a separate compartment. At each 
end of the compartment should be a groove or bevel, so that upon depressing 
either end of the slide the other may be easily grasped (Fig. 40). It is also desir- 
able to have the floor of the compartment grooved so that the slide rests only on 
two edges, thus preventing soiling the slide opposite the object. 
(3) Each compartment or each space sufficient to contain one slide of the 
standard size should be numbered, preferably at each end. If the compartments 
are made of sufficient width to receive two slides, then the double slides so fre- 
quently used in mounting serial 
sections may be put into the cab- 
inet in any place desired. 
(4) The drawers of the cabi- 
net should be entirely indepen- 
dent, so that any drawer may be 
partly or wholly removed with- 
out disturbing any of the others. 
(5) O11 the front of each draw- 
er should be the number of the 
drawer in Roman numerals, and 
the number of the first and last 
compartment in the drawer in 
Arabic numerals (Fig. 39). 
Fig- 39-—Cabinet for Micro- 
scopical Specimens, showing the 
method of arrangement and of 
numbering the drawers and in- 
dicating the number of the first 
and last compartment in each 
drawer. It is better to have the 
slides on which the drawers rest 
somewhat shorter, then the 
entFe and n<~d notched a° here shown. 
Fig. 39. 81 
MOUNTING AND LABELING. 
Fig. 40, A.—Part of a cabinet drawer seen from above. In compartment No. 96 
is represented a slide lying flat. The label of 
the slide and the number of the compartment 
are so placed that the number of the compart- 
ment may be seen through the slide. The seal- 
ing cement is removed at one place to show 
that in sealing the cover-glass, the cement is 
put partly on the cover and partly on the slide 
(2 168). 
Fig. 40, B.—This represents a section of the 
same part of the drawer, (a) Slide resting as in 
A No. 96. The preparation is seen to be above 
a groove in the floor of the compartment, (b) 
One end of the slide is seen to be uplifted by 
depressing the other into the bevel. 
MOUNTING OBJECTS—EXPERIMENTS. 
g 184. Mounting Dry, or in Air (g 170).—Pre- 
pare a shallow cell and dry it (§ 167). Select a 
clean cover-glass slightly larger than the cell. 
Pour upon the cover a drop of a 10 per cent, 
solution of salicylic acid in 95 per cent, alcohol. 
Let it dry spontaneously. Warm the slide till 
the cement ring or cell is somewhat sticky, 
then warm the cover gently and put it on the cell, pressing down all around (§ 170). 
Seal the cover, label and catalog ($$ 179, 181). 
A preparation of mammalian red blood corpuscles may be made very satisfac- 
torily by spreading a very thin layer of fresh blood on a cover with the end of a 
slide. After it is dry, warm gently to remove the last traces of moisture and 
mount precisely as for the crystals. One can get the blood as directed for the Mi- 
cro-spectroscopic work (| 146). 
$ 185. Mounting in Glycerin Jelly.—For this select some stained and isolated 
muscular fibers. Arrange them on the middle of a slide, using the centering card, 
and mount in glycerin jelly as directed in $ 174. Air bubbles are not easily re- 
moved from glycerin jelly preparations, so care should be taken to avoid them. 
$ 186. Mounting in Balsam by Desiccation (§ 176).—Find a fresh fly, or if in 
winter procure a dead one from a window sill or a spider’s web. Carefully remove 
the fly’s wings, being especially careful to keep them the dorsal side up. With a 
camel’s hair brush remove any dirt that may be clinging to them. Place a clean 
slide on the centering card, then with fine forceps put the two wings within one 
of the guide rings. Leave one dorsal side up, turn the other ventral side up. 
Spread some Canada Balsam on the face of the cover-glass and with the fine for- 
ceps place the cover upon the wings (PI. II, Fig. 14). Probably some air-bubles 
will appear in the preparation, but if the slide is put in a warm place these will 
soon disappear. Label, catalog, etc., (£ 176, 179, 181).* 
\ 187. Mounting in Balsam by Displacement (§§ 175, 177).—For this experi- 
ment select a stained section of any organ or tissue, as the skin, or ftiyel (spinal 
cord), then proceed exactly as described in $§ 175, 177. 
Fig. 40. 
* The Faber’s pencils for writing on glass, china, etc., are very convenient for 
writing temporary labels, etc., on slides and bottles. 82 
MOUNTING AND LABELING. 
PREPARATION OF MOUNTING MEDIA. 
$ i88. Glycerin.—One should procure pure glycerin for a mounting medium. 
It needs no preparation, except in some cases it should be filtered through filter 
paper or absorbent cotton to remove dust, etc. 
For preparing objects for final mounting, glycerin 50 cc., water 50 cc., form a 
good mixture. For many purposes the final mounting in glycerin is made in an 
acid medium, viz., Glycerin 99 cc., Glacial acetic or formic acid, 1 cc. 
By extreme care in mounting and by occasionally adding a fresh coat to the 
sealing of the cover-glass, glycerin preparations last a long time. They are liable 
to be very disappointing, however. In mounting in glycerin care should be taken 
to avoid air-bubbles, as they are difficult to get rid of. A specimen need not be 
discarded unless the air-bubbles are large and numerous. 
\ 189. Glycerin Jelly.—Soak 25 grams of the best dry gelatin in cold water in a 
small agate-ware dish. Allow the water to remain until the gelatin is softened. It 
usually takes about half an hour. When the gelatin is softened, as may be readily 
determined by taking a little in the fingers, pour off the superfluous water and 
drain well to get rid of all the water that has not been imbibed by the gelatin. 
Warm the softened gelatin over a water bath and it will melt in the water it has 
absorbed. Add to the melted gelatin about 5 cc. of egg albumen (white of egg) ; 
stir it in well and then heat the gelatin in the water bath for about half an hour. 
Do not heat above 750 or 8o° C., for if the gelatin is heated too hot it will be 
transformed into meta-gelatin and will not set when cold. The heat will coagu- 
late the albumen and form a kind of floculent precipitate which seems to gather 
all fine particles of dust, etc., leaving the gelatin perfectly clear. After the gela- 
tin is clarified it should be filtered through a hot filter and mixed with an equal 
volume of glycerin and 5 grams of chloral hydrate and shaken thoroughly. If it 
is allowed to remain in a warm place (i. e., in a place where the gelatin remains 
melted) the air-bubbles will rise and dissapear. 
In case the glycerin jelly remains fluid or semi-fluid at the ordinary temperature 
(i8°-2o° C.), the gelatin has either been transformed into meta-gelatin by too high 
temperature or it contains too much water. The amount of water may be lessened 
by heating at a moderate temperature over a water bath in an open vessel. 
This is a very excellent mounting medium. Air-bubbles should be avoided in 
mounting as they do not disappear. 
£ 190. Farrant’s Solution.—Take 25 grams of clean, dry, gum arabic ; 25 cc. of 
a saturated aqueous solution of arsenious acid ; 25 cc. of glycerin. The gum ara- 
bic is soaked for'several days in the arsenic water, then the glycerin is added and 
carefully mixed with the dissolved or softened gum arabic. 
This medium retains air-bubbles with great tenacity. It is much easier to 
avoid than to get rid of them in mounting. For the method of mounting in this 
see l 173. 
\ 191. Canada Balsam, Balsam of Fir.—This is one of the oldest and most sat- 
isfactory of the resinous media used for mounting microscopical preparations. 
Sometimes it is used in the natural state, but experience has shown that it is bet- 
ter to get rid of the natural volatile constituents. A considerable quantity, half a 
liter or more, of the natural balsam is poured into shallow plates in layers abont 1 
or 2 centimeters thick, then the plates are put in a warm, dry place, on the back 
of a stove or on a steam radiator, and allowed to remain until the balsam may be 
powdered when it is cold. This requires a long time, the time depending on the 
temperature and the thickness of the layer of balsam. 83 
MOUNTING AND LABELING. 
When the volatile products have evaporated, the balsam is broken into small 
pieces or powdered in a mortar and mixed with about an equal volume of xylol, 
turpentine or chloroform. It will dissolve in this and then should be filtered 
through absorbent cotton or a filter paper, using a paper funnel.* The balsam is 
too thin in this condition for mounting, but so made for the sake of filtering it. 
After it is filtered it is evaporated slowly in an open dish or a wide-mouth bottle 
or jar till it is of a syrupy consistency at the ordinary temperature. It is then 
poured into a bottle with a glass cap like a spirit lamp. For use it is put into a 
small spirit lamp (PI. V, Fig 47). 
The xylol is much the best substance to use for thinning the balsam. Such 
xylol balsam, as it is then called, may be used for mounting any object suitable 
for balsam mounting. The dehydration must be very perfect, however, as xylol 
is wholly immiscible with water. 
§ 192. Clearing Mixture ($ 175).—One of the most satisfactory and generally ap- 
plicable clearers is made by mixing carbolic acid crystals (Acidum carbolicum, 
A. phenicum crystallizatum) 40 cc. with rectified oil of turpentine {Oleum tere- 
binthinae redificatum) 60 cc. 
§ 193. Shellac Cement.—Shellac cement for sealing preparations and for making 
shallow cells ($§ 167, 168) is prepared by adding scale of bleached shellac to 95 
per cent, alcohol. The bottle should be filled about half full of the solid shellac 
then enough 95 per cent, alcohol added to fill the bottle nearly full. The bottle 
is shaken occasionally and then allowed to stand until a clear stratum of liquid 
appears on the top. This clear, supernatant solution is then filtered through 
absorbent cotton, using a paper funnel (§ 189), into an open dish or a wide-mouth 
bottle. To every 50 cc. of this filtered shellac 5 cc. of castor oil and 5 cc. of Vene- 
tian turpentine are added to render the shellac less brittle. This filtered shellac 
will be too thin and must be allowed to evaporate till it is of the consistency of 
thin syrup. It is then put into a capped bottle and for use into a small spirit 
lamp (PI. V, Fig. 47). In case the cement gets too thick add a small amount of 95 
per cent, alcohol or some thin shellac. 
§ 194. Liquid Gelatin.—Gelatin or clear glue 75 to 100 grams. Commercial 
acetic acid (No. 8) 100 cc., Water 100 cc., 95 per cent, alcohol 100 cc. Glycerin 15 
to 30 cc. Crush the glue and put it into a bottle with the acid, and set in a warm 
place, and shake occasionally. After three or more days add the other ingredi- 
ents. This solution is excellent for fastening paper to glass, wood or paper. The 
brush must be mounted in a quill or wooden handle. For labels, it is best to use 
linen paper of moderate thickness. This should be coated with the liquid gelatin 
and allowed to dry. The labels may be cut of any desired size and attached by 
simply moistening them as in using postage stamps. 
Very excellent blank labels are now furnished by dealers in microscopical sup- 
plies, so that it is unnecessary to prepare them one’s self except for special pur- 
poses. 
* For filtering balsam and all resinous and gummy materials, the writer has 
found a paper funnel the most satisfactory. It can be used once and then thrown 
away. Such a funnel may be very easily made by rolling a sheet of thick writing 
paper in the form of a cone and cementing the paper where it overlaps, or winding 
a string several times around the lower part. Such a funnel is best used in one of 
the rings for holding funnels. 84 
MOUNTING AND LABELING. 
g 194. Minute objects like diatoms and the scales of insects may be arranged in 
geometrical figures or in some fanciful way either for ornament or more satisfac- 
tory study. To do this the cover-glass is placed over the guide. This guide for 
geometrical figures may be a net-micrometer or a series of concentric circles. In 
order that the objects may remain in place, however, they must be fastened to the 
cover-glass. As an adhesive substance, liquid gelatin (£ 194) thinned with an 
equal volume of 50 per cent, acetic acid answers well. A very thin coating of this 
is spread on the cover with a needle or in some other way and allowed to dry. 
The objects are then placed on the gelatinized side of the cover and carefully got 
into position with a mechanical finger, made by fastening a cat’s whisker in a 
needle holder. For most of these objects a simple microscope with stand (Fig. 8) 
will be found of great advantage. After the objects are arranged, one breathes 
very gently on the cover-glass to soften the gelatin. It is then allowed to dry and 
if a suitable amount of gelatin has been used, and it has been properly moistened 
the objects will be found firmly anchored. In mounting, one may use Canada 
Balsam or mount dry on a cell (g$ 170, 176). See Newcomer, Amer. Micr. Soc’s 
Proc. 1886, p. 128 ; see also E. H. Griffith and H. E. Smith, Amer. Journal of Mi- 
cros., iv, 102, V, 87; Amer. Monthly Micr. Jour., i, 66, 107, 113. Cunningham, 
The Microscope, viii, 1888, p. 237. 
ARRANGING AND MOUNTING MINUTE OBJECTS- 
MICRO-CHEMISTRY AND CRYSTALEOGRAPHY—EXPERIMENTS. 
§ 196. The student of science and especially chemistry so frequently requires a 
knowledge of the appearance of minute crystals to aid in the determination of an 
unknown substance or for his information ill studying objects where crystals are 
liable to occur, that a few experiments have been introduced to give him a start in 
preparing and permanently mounting some of the common crystals. 
It is recommended that the crystals be made in several ways, that is from alco- 
holic solutions, aqueous solutions saturated and dilute, by spontaneous drying and 
crystallization and by rapid crystallization by the aid of heat. The modifications 
in crystallization under these different methods of treatment are frequently very 
striking. 
In every case the student is advised to study the appearance of the crystals in 
the “ mother liquor.” As a rule their characteristics are more clearly shown in 
the “mother liquor” than under any other conditions. 
It is of very great advantage to examine all crystalline forms with polarized 
light (§ 156). 
$ 197. Determination of the Character of the Solid Sediment in Water.—Take 
some of the sediment from a filter or allow a considerable volume of water to 
stand in a tall glass vessel to deposit its sediment. Take a concentrated drop of 
this sediment and mount it on a slide under a cover-glass. Study the preparation 
with the microscope. Probably there will be an abundance of animal and vegeta- 
table life as well as of solid sediment. Put a drop of dilute sulphuric acid 
(Acidum sulphuricinn dilutum, i. e., strong sulphuric acid 1 gram, water 9 grams) 
at the edge of the cover and at the opposite edge a small piece of the Japanese 
paper (PI. V, Pig. 49). The acid will gradually diffuse, and if the solid particles are 
carbonate of lime, minute bubbles will be seen to be given off. If they are silica 
or clay no change will result. Sulphuric acid is recommended for this, as the mi- 85 
MOUNTING AND LABELING. 
croscope would be far less liable to injury than as if some acid giving off fumes 
were used. 
i 198. Herapath’s Method of Determining Minute Quantities of Quinine.—For 
a so-called test fluid 12 c.c. of glacial acetic acid, 4 c.c. of 95 per cent, alcohol and 
7 drops of dilute sulphuric acid (§ 197) are mixed. A drop of the test fluid is put 
on a slide and a very minute amount of quinine added. After this is dissolved, 
add an extremely minute drop of an alcoholic solution of iodine. “The first ef- 
fect is the production of the yellow cinnamon-colored compound of iodine and 
quinine which forms as a small circular spot; the alcohol separates in little drops, 
which by a sort of repulsive movement, drive the fluid away ; after a time, the 
acid liquid again flows over the spot, and the polarizing crystals of sulphate of iodo- 
quinine are slowly produced in beautiful rosettes. This succeeds best without the 
application of heat.” Dr. Herapath used this method to determine the presence 
of quinine in the urine of patients under quinine treatment. See Hogg, p. 150; 
Quarterly Jour. Micr. Sc., vol. ii, pp. 13-18. For further papers on micro-chem- 
istry by Dr. Herapath, see the Royal Society’s Catalog of Scientific Papers. 
£ 199. List of Substances for the Study of Crystallography with the Micro- 
scope.*—The substances are crystallized on the cover glass in all cases, and in all 
cases, except where otherwise stated, a saturated aqueous solution of the substance 
was first prepared. 
1. Ammonium chloride ; 2. Ammonium copper chloride ; 3. Barium chloride ; 
4. Cobalt chloride (Beautiful crystals obtained by mixing the saturated aqueous 
solution with an equal volume of 95 per cent, alcohol. Crystallization in a cur- 
rent of dry air some distance above an alcohol or Bunsen flame ; Mount in xylol 
balsam (§$ 176, 191). 5. Copper acetate ; Mount dry (§ 170). 6. Copper sulphate. 
Crystals much more satisfactory when examined in the “ mother liquor.” 7. Lead 
nitrate ; 8. Mercuric chloride (Corrosive sublimate), mount in xylol balsam (§§ 176, 
191). 9. Nickel nitrate; obtain crystals by heating. Mount in xylol balsam 
($$ 186, 191) ; 10. Potash alum; 11. Potassium chlorate; 12. Potassium dichro- 
mate. Compare specimen crystallized by heat and spontaneously ; mount dry or 
in xylol balsam (§§ 170, 176). 13. Potassium iodide. Dilute with one or two vols. 
water and crystallize by heat. 14. Potassium nitrate ; 15. Potassium oxalate ; 16. Po- 
tassium sulphate ; 17. Salicine. Fuse the dry salicine on the cover-glass, mount 
dry ($ 170) ; 17. Salicylic aeid. Make a 10 per cent, solution in 95 per cent, alco- 
hol. Let it crystallize spontaneously in the air. Mount dry ($ 170); 18. Sodium 
chloride (common salt). Mix sat. aq. sol. with one or two volumes of water, and 
heat. Mount dry or in balsam ()j§ 170, 176). 
| 200. For directions and hints in micro-chemical work and crystallography, 
consult the various volumes of the Journal of the Roy. Micr. Soc., Zeitsclirift fur 
physiologische Chemie and other chemical journals ; Wormly ; Klement & Reg- 
nard ; Carpenter ; Hogg ; Behrens Kossel und Sehiefferdecker ; P'rey. 
* Most of the chemicals here named were suggested to the writer by Prof. L. M. 
Dennis of the Chemical Department. BIBLIOGRAPHY. 
The books and periodicals named below in alphabetical order, are in the labora- 
tory or the University library. They pertain wholly or in part to the microscope 
microscopical or histological methods. They are referred to in the text by initial 
letters or by fuller, recognizable abbreviations. 
For current microscopical and histological literature, the Journal of the Royal 
Microscopical Society, the Index Medicus, the Zoologischer Anzeiger, and the 
Zeitschrift fur wissenschaftliche Mikroskopie, Anatomischer Anzeiger, Biolog- 
isches Centralblatt and Physiologisches Centralblatt, taken together furnish nearly 
a complete record. 
References to books and papers published in the past may be found in the peri- 
odicals just named, in the Index Catalog of the Surgeon General’s library ; in the 
Royal Society's Catolog of Scientific Papers, and in the bibliographical references 
given in special papers. 
BOOKS. 
Angstrom.—Reclierches sur le spectre solaire, spectre normal du soleil. Up- 
sala, 1868. 
Anthony, Wm. A., and Brackett, C. F.—Elementary text-book of physics. 7th 
ed. Pp. 527, 165 Fig. New York, 1891. 
Bausch, E.—Manipulation of the microscope. Pp. 95, illustrated. Rochester, 
1891. 
Beale, L. S.—How to work with the microscope. 5th ed. Pp. 518, illustrated. 
London, 1880. Structure and methods. 
Beauregard, H., at Galippe, V.—Guide de l’eleve et du praticien pour les trav- 
aux pratiques de micrographie, comprenaut la technique et les applications du 
microscope a l’histologie vegetale, k la physiologie, a la clinique, a la hygiene et a 
la mddecine legale. Pp. 904, 570 Fig, Paris, 1880. 
Behrens, J. W.—The microscope in botany. A guide for the microscopical in- 
vestigation of vegetable substances. Translated and edited by Hervey and Ward. 
Pp. 466, illustrated. Boston, 1885. 
Behrens, W., Kossel, A., und Schiefferdecker, P.— Das Mikroskop und die 
Methoden der mikroskopischeu Untersuchung. Pp. 315, 193 Fig. Braunschweig. 
Browning, J.—How to work with the micro-spectroscope. Referred to in Beale 
and Carpenter. 
Carnoy, J. B., Le Chanoine.—La Biologie Cellulaire; Etude comparee de la 
cellule dans les deux regnes. Illustrated (incomplete). Paris, 1884. Structure 
and methods. 
Carpenter, W. B.—The microscope and its revelations. 6th ed. Pp. 882, illus- 
trated. London and Philadelphia, 1881. Methods and structure. 
Cooke, M. C.—One thousand objects for the microscope. Pp. 123. London, no 
date. 500 figures and brief descriptions of pretty objects for the microscope. 
Daniell, A.—A text-book of the principles of physics. Pp. 653, 254 Fig. Lon- 
don, 1884. 87 
BIBLIOGRAPHY. 
Dippel, L.— Grundziige der allgemeinen Mikroskopie. Pp. 524, 245 Fig. 
Braunschweig, 1885. Excellent discussion of the microscope and accessories. 
Ebner, V. v.—Untersucliungen iiber die Ursachen der Anisotropie organischer 
Substauzen. Leipzig, 1882. Large number of references. 
Ellenberger, W.—Handbuch der vergleichenden Histologie und Physiologie 
der Haussaugethiere. Berlin, 1884-f-. 
Fol, H.—Lehrbuch der vergleichenden mikroskopischen Anatomie, mit Ein- 
schluss der vergleichenden Histologie und Histogenie. Illustrated (incomplete). 
Leipzig, 1884. Methods and structure. 
Foster, P'rank P.—An illustrated encyclopaedic medical dictionary, being a dic- 
tionary of the technical terms used by writers on medicine and the collateral sci- 
ences in the Latin, English, French and German languages. Illustrated, quarto 
volumes. Vol. I, 1888 ; Vol. II, 1890 ; Vol. Ill, in press. 
Frey, H.—The microscope and microscopical technology. Translated and ed- 
ited by G. R. Cutter. Pp. 624, illustrated. New York, 1880. Methods and 
structure. 
Frey, H.—Hand-book of the histology and histo-chemistry of man. Translated 
by Barker. Illustrated. New York, 1875. Structure and chemistry. Also the 
5th German edition. Leipzig, 1876. 
Gamgee, A.—A text-book of the physiological chemistry of the animal body. 
Part I, pp. 487, 63 Fig. London and New York, 1880. Structure and methods. 
Gibbs, H.—Practical histology and pathology. Pp. 107. London, 1880. Meth- 
ods. 
Goodale, G. L.—Physiological botany. Pp. 499 L36, illustrated. New York, 
1885. Structure and methods. 
Halliburton, W. D.—A text-book of chemical physiology and pathology. Pp. 
874, 104 illus. London and New York, 1891. 
Hogg, J.—The microscope, its history, construction and application. New edi- 
tion, illustrated. Pp. 764. London and New York, 1883. Much attention paid 
to the polariscope. 
James, F. L.—Elementary microscopical technology. Part I, the technical his- 
tory of a slide from the crude material to the finished mount. Pp. 107, illustrated. 
St. Louis, 1887. 
Element and Regnard.—Reactions microcliemiques a cristaux et leur applica- 
tion en analyse qualitative. Pp. 126, 8 plates. Bruxelles, 1886. 
Kraus, G.—Zur Kentniss der ChlorophyllfarbstofFe. Stuttgart, 1872. 
Le Conte, Joseph.—Sight—an exposition of the principles of monocular and bi- 
nocular vision. Pp. 275, illustrated. New York, 1881. 
Lee, A. B.—The microtomist’s vade-mecum. A hand-book of the methods of 
microscopic anatomy. 
Lehmann, C. G.—Physiological chemistry. 2 vols. Pp. 648+547, illustrated. 
Philadelphia, 1855. 
Lehmann, O.—Molekularphysik mit besonderer Beriicksichtigung mikroskop- 
ischer Untersucliungen und Anleitung zu solchen, sowie einem Auhang fiber 
mikroskopische Analyse. 2 vols. Illustrated. Leipzig, 1888-1889. 
Lockyer, J. N.—The spectroscope and its application. Pp. 117, illustrated. 
London and New York, 1873. 
M’Kendrick, J. G.—A text-book of physiology. Vol. I, general physiology. 
Pp. 516, 318 illus. New York, 1888. 
Macdonald, J. D.—A guide to the microscopical examination of drinking water. 
Illustrated. London, 1875. Methods and descriptions. 88 
BIBLIOGRAPHY. 
MacMunn, C. A.—The spectroscope in medicine. Pp. 325, illustrated. Lon- 
don, 1885. 
May all, Jr , John.—Cantor lectures on the microscope, delivered before the so- 
ciety for the encouragement of arts, manufactures and commerce. Nov.-Dee., 
1885. (History of the microscope, and figures of many of the forms used at vari- 
ous times). 
Nageli und Schwendener.—Das Mikroskop, Theorie und Anwendung desselben. 
2d ed. Pp. 647, illustrated. Leipzig, 1877. 
Phin,J.—Practical hints on the selection and use of the microscope for begin- 
ners. 6th edition. Illustrated. New York, 1890. 
Preyer, W.—Die Blutkrystalle. Jena, 1871. Full bibliography to that date. 
Pringle, A.—Practical photo-micrography. Pp. 193, illustrated. New York, 
1890. 
Proctor, R. A.—The spectroscope and its work. London, 1882. 
Prudden, T. M.—A manual of practical normal histology. Pp. 265. 2d ed. 
New York, 1885. Methods and structure. 
Queckett, J.—A practical treatise on the use of the microscope, including the 
different methods of preparing and examining animal, vegetable and mineral 
structures. Pp, 515, 12 plates. 2d ed. London, 1852. 
Ranvier, L.—Trait6 technique d’histologie. Pp. 1109, illustrated. Paris, 1875- 
1888. Structure and methods. Also German translation 1888. 
Reference Hand-Book of the medical sciences. Albert H. Buck, editor. 8 
quarto vols. Illustrated with many plates, and figures in the text. New York, 
1885-1889. 
Richardson, J. G.—A hand-book of medical microscopy. Pp. 333, illustrated. 
Philadelphia, 1871. Methods and descriptions. 
Robin, Ch.—Traite du microscope et des injections. 2d ed. Pp. 1101, illustrat- 
ed, Paris, 1877. Methods and structure. 
Roscoe, Sir Henry.—Lectures on spectrum analysis. 4th. ed. London, 1885. 
Rutherford, W.—Outlines of practical histology. 2d ed. Illustrated. Pp. 194. 
London and Philadelphia, 1876. Methods and structures. 
Satterthwaite, F. E. (editor).—A manual of histology. Pp. 478, illustrated. 
New York, 1881. Structure and methods. 
Schafer, E. A.—A course of practical histology, being an introduction to the use 
of the microscope. Pp. 304, 40 Fig. Philadelphia, 1877. Methods. 
Scliellen, H.—Spectrum analysis, translated by Jane and Caroline Lassell. Ed- 
ited with notes by W. Huggins. 13 plates, including Angstrom’s and Kirchhoff’s 
maps. London, 1885. 
Science Lectures at South Kensington. 2 vols. Pp. 290 and 344, illustrated. 
One lecture on microscopes and one on polarized light. London, 1878-1879. 
Seiler, C.—Compendium of microscopical technology. A guide to physicians 
and students in the preparation of histological and pathological specimens. Pp. 
130, illustrated. New York, 1881. 
Silliman, Benj., Jr.—Principles of physics, or natural philosophy. 2d edition, 
rewritten. Pp. 710, 722 illustrations. New York and Chicago, i860. 
Stowell, Chas. H.—The students’ manual of histology, for the use of students, 
practitioners and microscopists. 3d ed. Pp. 368, illustrated. Ann Arbor, 1884. 
Structure and methods. 
Strasburger, E.— Das botanische Practicum. Anleitung zum Selbststudium 
der mikroskopischen Botanik, fiir Anfanger und Fortgeschrittnere. Pp. 664, illus- 
trated. Structure and methods. Also English translation. 89 
BIBLIOGRAPHY. 
Suffolk, W. T.—On microscopical manipulation. 2d ed. Pp. 227, illustrated. 
London, 1870. 
Suffolk, W. T.—Spectrum analysis applied to the microscope. Referred to in 
Beale. 
Trelease, Wm.—Poulsen’s botanical micro-chemistry, an introduction to the 
study of vegetable histology. Pp. 11S. Boston, 1884. Methods. 
Valentin, G.—Die Untersuchung der Pflanzen uud der Thiergewebe in polarisir- 
tem Liclit. Leipzig, 1861. 
Vierordt.—Die quantitative Spectral analyse in ihrer Anwendung auf Physiologie, 
Chemie und Technologie. Tubingen, 1874. 
Whitman, C. O.—Methods of research in microscopical anatomy and embryolo- 
gy. Pp. 255, illustrated. Boston, 1885. 
Wilder and Gage.—Anatomical Technology as applied to the domestic cat. An 
introduction to human, veterinary and comparative anatomj\ Pp. 575, 130 Fig. 
2d ed. New York and Chicago, 1886. 
Wood, J. G.—Common objects for the microscope. Pp. 132. London, no date. 
Upwards of 400 figures of pretty objects for the microscope, also brief descriptions 
and directions for preparation. 
Wormly, T. G.—The micro-chemistry of poisons. 2d ed. Pp. 742, illustrated. 
Philadelphia, 1885. 
Wythe, J. H.—The microscopist, a manual of microscopy and a compendium 
of microscopical science. 4U1 ed. Pp. 434, 252 Fig. Philadelphia, 1880. 
See also Watt’s Chemical dictionary, and the various general and technical en- 
cyclopaedias. 
PERIODICALS 
The American journal of microscopy and popular science. New York, 1876- 
1881. Illustrated. Methods and structure. 
The American monthly microscopical journal. Illustrated. 1880+. Methods 
and structure. 
American naturalist. Illustrated. Salem and Philadelphia, 1867-!-. Methods 
and structure. 
American quarterly microscopical journal, containing the transactions of the 
New York microscopical society. Illustrated. New York, 1878. Structure and 
methods. 
American society of microscopists. Proceedings. Illustrated. 1878+. Meth- 
ods and structure. 
Anatomischer Anzeiger. Ceutralblatt fur die gesammte wissenschaftliche Ana- 
tomie. Amtliches Organ der anatomischen Gesellschaft. Herausgegeben von 
Dr. Karl Bardeleben. Jena, 1886-j— Besides articles relating to the microscope 
or histology, a full record of current anatomical literature is given. 
Archiv fur mikroscopische Anatomie. Illustrated. Bonn, 1S65-J-. Structure 
and methods. 
Ceutralblatt fur Physiologie. Unter Mitwirkung der physiologisclieu Gesell- 
schaft zu Berlin. Herausgegeben von S. Exner und J. Gad. Leipzig uud Wien, 
*NoTE.—When a periodical is no longer published, the dates of the first and 
last volumes are given ; but if still being published, the date of the first volume is 
followed by a plus sign. 90 
BIBLIOGRA PH Y. 
1887+. Brief extracts of papers having a physiological bearing. Full biblio- 
graphy of current literature. 
Index Medicus. New York, 1879+. Bibliography, including histology and 
microscopy. 
Journal of anatomy and physiology. Illustrated. London and Cambridge, 
1867+. Structure and methods. 
Journal de micrographie. Illustrated. Paris, 1877+. Methods and Structure. 
Journal of the New York microscopical society. Illustrated. New York, 1885+. 
Methods and structure. 
Journal of Physiology. Illustrated. London and Cambridge, 1878+. 
Journal of the American Chemical Society. New York, 1879+. 
Journal of the Chemical Society. Loudon, 1848+. 
Journal of the royal microscopical society. Illustrated. London, 1878+. Bib- 
liography of works and papers relating to the microscope, microscopical methods 
and histology. It also includes a summary of many of the papers. 
The Lens, a quarterly journal of microscopy and the allied natural sciences, 
with the transactions of the state microscopical society of Illinois. Illustrated. 
Chicago, 1872-1873. Methods and structure. 
The Microscope. Illustrated. Trenton, N. J., 1881-}-. Methods and structure. 
Microscopical Bulletin, and science news. Illustrated. Philadelphia, 1883+. 
The editor, Bdward Pennock, introduced the term “par-focal” for oculars (see 
vol. iii, p. 31, also, the note to \ 48, p. 18). 
Monthly microscopical journal. Illustrated. London, 1869-1877. 
Nature. Illustrated. London, 1869+. 
Philosophical Transactions of the Royal Society of London. Illustrated. Lon- 
don, 1665+. 
Proceedings of the Royal Society. London, 1854+. 
Quarterly journal of microscopical science. Illustrated. London, 1853+. 
Structure and methods. 
Science Record. Boston, 1883-4. Methods and structure. 
Zeitschrift fur Instrumentenkunde. 
Zeitschrift fur pliysiologische Cliemie. Strassburg, 1877+. 
Zeitschrift fiir wissenschaftliche Mikroskopie und fur mikroskopische Technik. 
Illustrated. Braunsch. 1S84+. Methods and bibliography. 
Besides the above-named periodicals, articles on the microscope or the applica- 
tion of the microscope appear occasionally in nearly all of the scientific journals. 
One is likely to get references to these articles through the Jour. Roy. Micr. Soc. 
or the Zeit. wiss. Mikroskopie. INDEX. 
A 
Abbe camera lucida, 48 ; arrangement of, 
49; drawing with, 51; hinge for 
prism, 52 ; inclined microscope wdth, 
50; laboratory microscope with, 28. 
Abbe condenser, 19. 
Abbe illuminator, 19; experiments, 20, 
laboratory microscope with, 28; 
light, axial and oblique, 20; mirror 
with, 20. 
Aberration, chromatic, 4 ; spherical, 4. 
Absorption spectra, 54, 55, 56; amount 
of material necessary and its proper 
manipulation, 59; Angstrom and 
Stokes’ law of, 55 ; banded, not given 
by all colored objects, 61 ; of blood, 
60; of colored minerals, 62 ; of per- 
mangate of potash, 60. 
Achromatic objectives, 3, 4 ; triplet, 2. 
Achromatism, 4. 
Adjustable objectives, 5 ; and microme- 
try, 46. 
Adjusting collar, graduation of, 23. 
Adjustment of analyzer, 63 ; of object- 
ive, 5, 22 ; of objectives for cover- 
glass, specific directions, 23 ; with 
graduated collar, 23. 
Aerial image, 13. 
Air bubbles, 31 ; with central and oblique 
illumination, 31. 
Air and oil, distinguished optically, 32 ; 
by reflected light, 32. 
Amici prism, 54. 
Ampl fier, 39. 
Amplification of microscope, 36. 
Analyzer, 63 ; adjustment and putting in 
position, 63. 
Angle of aperture, 6, 7. 
Angstrom and Stokes’ law of absorption 
spectra, 55. 
Angular aperture, 6, 7. 
Anisotropic, 64. 
Aperture of objective, 6, 7 ; angular, 6, 
7 ; formula for, 7 ; numerical, 7. 
Aplanatic objectives, 4. 
Apochromatic objectives, 4. 
Apparatus and material, 1, 29, 36, 54, 66. 
Appearances, interpretation, 29. 
Arranging and mounting minute ob- 
jects, 84. 
Axial light, 16; experiments, 19; with 
Abbe illuminator, 20. 
Axial point, 6 ; ray, 16. 
Axis, optic, 6, 16. 
B 
Back combination or system of objec- 
tive, 3, 5. 
Bacillus tuberculosis, 25. 
Balsam, Canada, preparation of, 82 ; re- 
moval from lenses, 27. 
Banded absorption spectra not given by 
all colored objects, 61. 
Birefringeut, 64. 
Blood, absorption spectrum of, 60; or 
other albuminous material, remov- 
al, 26. 
Bread crumbs, examination of, 35. 
Brownr n movement, 34. 
Brunswick black, removal from lenses, 
27- 
Bubble, air, 31. 
Burning point, 2. 
Butterfly scales, 35. 
c 
Cabinet for microscopical preparations, 
80. 
Camera lucida, Abbe, 48, arrangement 
of, 49, drawing with, 51, hinge for 
prism, 52, with inclined microscope, 
5°; 
Camera lucida, definition, 47 ; Wollas- 
ton’s, 38, 48. 
Canada balsam, preparation of, 82 ; re- 
moval from lenses, 27. 
Carbonate of lime, pedesis, 35. 
Card, centering, 74. 
Care of eyes, 27 ; microscope, mechani- 
cal parts, 25, optical parts, 26 ; water 
immersion objectives, 24. 
Carmine to show currents and pedesis, 
84- 
Catalogs and labels, ink for, 79. 
Cataloging, formula, 79; preparations, 
79- 
Cells, mounting, 71. 
Centering and arrangement of illumin- 
ator, 19, 20; 
Centering card, 74. 
Central light, 16; with a mirror, 19. 
Chromatic aberration, 4; correction, 4. 
Chemical focus, 4; rays, 4. 
Cleaning back lens of objective, 27 ; 
homogeneous objectives, 25 ; mix- 
tures for glass, 70 ; slides and cover 
glasses, 66-7 ; 92 
INDEX. 
Clearer, clearing, 75. 
Clearing mixture, preparation of, 83. 
Clothes moth, examination of scales, 35. 
Cloudiness, of objective and ocular, how 
to determine, 29, 30; removal, 26. 
Coarse adjustment of microscope, 12. 
Collective, 9. 
Collodion for coating glass rod, 33. 
Color images, 22, 25 ; law of, 55. 
Colored minerals, absorption spectra of, 
62 ; substances, spectra of, 55. 
Coma, 23. 
Combination of lenses, back and front, 3. 
Comparison prism, 57 ; spectrum, 57. 
Compensating ocular, 4, 9. 
Complementary spectra, 56. 
Compound microscope, see under micro- 
scope. 
Concave lenses, 4 ; mirror, use of, 17. 
Condenser, x ; Abbe, 19 ; optic axis of, 
20. 
Condensing lens, 20. 
Continuous spectrum, 54. 
Contoured, doubly, 33. 
Converging lens, 1,3; lens-system, 3. 
Convex lenses, 4. 
Corn starch, examination of, 35. 
Correction, chromatic, 4. 
Cotton, examination of, 35. 
Cover-glass, or covering glass, 67 ; ad- 
justment, specific directions, 23 ; ad- 
justment and tube length, 24 ; clean- 
ing, 67, 68; larger than object, 67 ; 
measurer, 69 ; measuring thickness 
of, 68; non-adjustable objectives, 
table of thickness, 6 ; No. x, varia- 
tion of thickness, 68 ; putting on, 
74 ; sealing, 71-72 ; tester, 69 ; thick- 
ness of, 5 ; wiping, 67. 
Currents in liquids, 34. 
Crystals from frog for pedesis, 35. 
Crystallization under microscope, 22. 
Crystallography, 84; list of substances 
for, 84. 
D 
Damar, removal from lenses, 27. 
Dark-ground illumination with Abbe il- 
luminator, 21 ; with mirror, 2r. 
Dehydration, 75. 
Desiccation in mounting objects in resin- 
ous media, 75, 76. 
Designation of oculars, 10. 
Determination of magnification, 38. 
Diaphragms and their employment, x 6 ; 
effect of one too small, 30 ; iris, x6 ; 
ocular, 12; pin-hole, 20; size and 
position of opening, 16 ; 
Diffraction grating, 54. 
Direct light, 15 ; vision spectro-scope, 54. 
Dispersing prism, 54. 
Displacements, in mounting objects in 
resinous media, 75-76. 
Distance, standard at which the virtual 
image is measured, 39 ; working d. 
of simple microscope or objective, 
15; working d. of compound micro- 
scope, 15. 
Distinctness of outline, 32. 
Distortion in drawing, avoidance of 48 ; 
spherical, 4. 
Dividers, measuring spread of, 37. 
Double spectrum, 57. 
Doubly contoured, 33. 
Draw-tube, pushing in, 18. 
Drawing with Abbe camera lucida, 51, 
52 ; distance at which done (250111m. 
more or less), 40 ; distortion, avoid- 
ance of, 48; with microscope, 47 ; 
regulating size of, 52 ; scale and en- 
largement, 53 ; size of, and magnifi- 
cation of microscope with Abbe cam- 
era lucida, 52. 
Dry objectives, 4 ; for laboratory micro- 
scope, 28. 
Dust of living rooms, examination of, 
35 ; on objectives and oculars, how 
to determine, 29, 30 ; removal, 26. 
E 
Erect image, 1. 
Equivalent focal length, 3 ; focus of ob- 
jectives, 3 ; focus of oculars, 10. 
Examination of dust of living rooms, 
bread crumbs, corn starch, fibres of 
cotton, linen, silk, human and ani- 
mal hairs, potato, rice, scales of but- 
terflies and moths, wheat, 35. 
Experiments, Abbe illuminator, 20; 
with adjustable and immersion ob- 
jectives, 22-25; compound micro- 
scope, 10; homogeneous immersion 
objective, 24 ; lighting and focusing, 
17 ; with micro-spectroscope, 60; 
with micro-polarizer, 64 ; in mount- 
ing, 81 ; simple microscope, 2. 
Extraordinary ray of polarized light, 63. 
I Eyes, care of, 27 ; effect on magnifica- 
tion, 40. 
Eye-lens of the ocular, 8, 9. 
Eye-piece, 8 ; micrometer, 42. 
Eye-point, 2 ; of ocular, demonstration, 
14. 
Eye-shade, Ward’s, 27, double, PI. II. 
F 
Farrant’s solution, in mounting objects, 
order of procedure, 74 ; preparation 
of, 82. 
Feather, examination of, 35. 
Fibers, examination of, 35. 
Field, 2 ; with orthoscopic ocular, 12 ; 
with periscopic ocular, 12 ; of view 
with microscope, 11, 36, 47. INDEX. 
93 
Field-lens, 8, 9; action of, 14; of ocular, 8. 
Filter paper, Japanese, 26. 
Filtering balsam, etc., paper funnel for, 
83-. 
Fluid, immersion, 4. 
Focal distance or point, principal, 3 ; 
length, equivalent, 3 ; 
Focus, 2 ; always up, 18; chemical, 4 ; 
of objectives, equivalent, 3 ; of ocu- 
lars, equivalent, 10 ; optical, 4 ; prin- 
cipal, 1-3. 
Focusing, 2, 15 ; with compound micro- 
scope, 15 ; experiments, 17 ; with 
high objectives, 18; with low ob- 
jectives, 17 ; objective for micro- 
spectroscope, 59 ; with simple micro- 
scope, 15 ; slit of micro-spectroscope, 
56. 
Fraunhofer lines, 55. 
Front combination or lens of objective, 
3 ; system, 5. 
Function of objective, 12, 13 ; of ocular, 
13. 14- 
G 
Gelatin, liquid, preparation of, 83. 
Glass, cleaning mixture for, 70 ; rod ap- 
pearance under, microscope, 33 ; 
slides or slips, 66 
Glue, liquid, preparation of, 83. 
Glycerin, mounting objects in, order of 
procedure, 73 ; removal, 26. 
Glycerin jelly, mounting objects in, or- 
der of procedure, 74; preparation 
of, 82. 
Gold size, removal from lenses, 27. 
Goniometer ocular, 9. 
Graduation of adjusting collar, 23. 
Grating, diffraction, 54. 
Ground glass, preparation of, 12. 
H 
Haemaglobin, 61 ; reduced h., 61. 
Hairs, examination of, 35. 
Herapath’s method of determining mi- 
nute quantities of quinine, 85. 
High oculars, 5, 9. 
Highly refractive, 33. 
Homogeneous immersion objectives, 4 ; 
cleaning 25 ; experiments, 24 ; for 
laboratory microscope, 28. 
Homogeneous liquid, 25. 
Huygenian ocular, 9. 
I-J 
Illumination for Abbe camera lucida, 51 ; 
artificial, 15, 20; central with air and 
oil, 31 ; dark-ground, 16; dark- 
ground, with Abbe illuminator, 21 ; 
dark-ground, with mirror, 21 ; 
oblique, with air and oil, 32 ; for 
Wollaston’s camera lucida, 48. 
Illuminator, i ; Abbe, 19 ; Abbe, axial 
and oblique light, 20; Abbe, exper- 
iments, 20; Abbe, mirror and light 
for, 20 ; centering and arrangement, 
19, 20; immersion, 20. 
Image, aerial, 13 ; color, 22, 25 ; erect, 
1 ; inverted, 1 ; inverted, real of ob- 
jective, 13; real, 1; real, inverted, 
3 ; refraction, 22, 25. 
Immersion fluid, 4; illuminator, 20; 
liquid, 4 ; objective, 4, 24. 
Incandescence spectra, 56. 
Incident light, 15. 
Index of refraction of medium in front 
of objective, 7. 
Ink for labels and catalogs, 79. 
Interpretation of appearances under the 
microscope, 29. 
Inverted image, 1. 
Iris diaphragm, 16. 
Isotropic, 64. 
Japanese filter or tissue paper, 12, 13, 26. 
L 
Isabels and catalogs, ink for, 79; prep- 
aration of, 79. 
Labeling microscopical preparations, 77, 
serial sections, 78. 
Laboratory compound microscope, 27. 
Lamp-light, 20. 
Lenses, combination of, 3 ; concave, 4; 
condensing, 20; converging, 1, 3; 
convex, 4 ; systems of, 3. 
Lens-system, 1 ; converging, 3. 
Letters in stairs, 30. 
Light with Abbe illuminator, 20 ; axial, 
16 ; axial with Abbe illuminator, 20; 
direct, 15 ; central, 16 ; incident, 15 ; 
oblique, 16; oblique, experiments, 
19 ; oblique with Abbe illuminator, 
20; polarized, 63; reflected, inci- 
dent or direct, 15 ; transmitted, 16 ; 
wave length of, 58. 
Lighting, 15 ; for Abbe camera lucida, 
51 ; artificial, 15 ; experiments, 17 ; 
axial, experiments, 19; kind of light, 
15 ; for micro-polariscope, 63 ; for 
micro-spectroscope, 58 ; with a mir- 
or, 17; 
Line spectrum, 54. 
Linen, examination of, 35. 
Liquid, currents in, 34; homogeneous, 
25 ; immersion, 4. 
M 
Magnification, effect of adjusting object- 
ive, 46 ; determination of, 38 ; ex- 
pressed in diameters, 36 ; method of 
binocular or double vision in obtain- 
ing, 36-37 ; of microscope, 36 ; of 
microscope with Abbe camera lucida, 94 
INDEX. 
52 ; of microscope, compound, 37 ; 
of microscope, simple, 36 ; relation 
to eyes, 40 ; varying with compound 
microscope, 39.. 
Magnifier, 2. 
Magnifying power of microscope, 36. 
Malezeit sand, spectrum of, 62. 
Marking objects, 11, note. 
Material and apparatus, 1, 29, 36, 54, 66. 
Measurer, cover-glass, 69. 
Measuring the spread of dividers, 37. 
Mechanical parts of compound micro- 
scope, 3 ; of laboratory microscope, 
28 ; of microscope, care of, 25. 
Mechanical stage, 28. 
Medium, mounting, 5, 7. 
Micro-chemistry, 84. 
Micrometer, filling lines of, 37 ; object 
or objective, 37 ; ocular or eye-piece, 
10, 42, 43 ; ocular, micrometry with, 
44 ; ocular, valuation of, 43 ; ocular, 
varying valuation of, 44; ocular, 
ways of using, 45 ; stage, 37. 
Micrometry, definition, 40 ; with adjust- 
able objectives, 46: comparison of 
methods, 46-47 ; with compound mi- 
croscope, 41 ; by dividing the size of 
image by magnification of micro- 
scope, 42 ; limit of accuracy in, 46 ; 
with ocular micrometer, 44; with 
simple microscope, 41 ; remarks on, 
46 ; by stage micrometer and camera 
lucida, 42 ; by stage micrometer on 
which is mounted the object, 42 ; 
unit of measure in, 41. 
Micro-millimeter, 41. 
Micron, 41 ; for measuring wave-length 
of light, 58. 
Micro-polariscope, 35, 62 ; for laboratory 
microscope, 28 ; lighting for, 63 ; ob- 
j ectives to use with, 63 ; purpose of, 
64. 
Microscope, definition, 1 ; adjustment, 
12 ; amplification of, 36 ; care of, 25 ; 
field of, 11 ; focusing, 15 ; magnifi- 
cation, 36 ; polarizing, 34. 
Microscope compound, definition, 1 ; 
drawing with, 47 ; experiments with, 
10; focusing with, 15 ; for labora- 
tory, 27 ; magnification or magnify- 
ing power, 36, 37 ; magnification and 
size of drawing with Abbe camera 
lucida, 52 ; mechanical parts of, 3 ; 
micrometry with, 41 ; optic axis of, 
16 ; optical parts of, 3 ; polarizing, 
pedesis with, 34 ; stand of, 1 ; vary- 
ing magnification, 39. 
Microscope, simple, definition, 1 ; ex- 
periments with, 2 ; focusing with, 
15 ; magnification of, 36; microm- 
etry with, 4T. 
Microscopic objective, 3; ocular, 8; 
slides or slips, 66. 
Microscopical preparations, cabinet for, 
80 ; cataloging, 79 ; labeling, 77 ; 
tube-length, 5. 
Micro-spectroscope, 54; adjusting, 56; 
experiments, 60 ; for laboratory mi- 
croscope, 28 ; lighting for, 58 ; ob- 
jectives to use with, 59 ; slit-mechan- 
ism of, 54. 
Micrum, 41. 
Mikron, 41. 
Minerals, colored, absorption spectra of, 
62. 
Mirror, 1 ; for Abbe illuminator, 20; 
concave, use of, 17 ; light with, cen- 
tral and oblique, iq; lighting with, 
17 ; plane, use of, 17 ; position of con- 
cave, 17. 
Molecular movement, 34. 
Mouo-refringeut, 64. 
Mounting cells, preparation of, 71 ; me- 
dium, 5, media, preparation of, 82. 
Mounting objects, dry in air, order of 
procedure, 73 ; examples in air, gly- 
cerin jelly and balsam, 81 ; in Far- 
rant’s solution, order of procedure, 
74 ; in glycerin, order of procedure, 
73 ; in glycerin jelly, order of pro- 
cedure, 74 ; in media miscible with 
water, 73 ; microscopical objects, 70 ; 
in resinous media, by drying or des- 
iccation, order of procedure, 75, 76; 
in resinous media by successive dis- 
placements, order of procedure, 75, 
76. 
Movement, Brownian, or, molecular, 34. 
Myopia, effect on magnification, 40. 
N 
Negative oculars, 8, 9. 
Net-micrometer, 50. 
Nicol prism, 62. 
Nomenclature of objectives, 3. 
Non-achromatic objectives, 4. 
Noil-adjustable objectives, 5 ; thickness 
of cover-glass for, table, 6. 
Nose-piece, 11. 
Numerical aperture of objectives, 7. 
o 
Object micrometer, 37 ; putting under 
microscope, 11 ; having plane or ir- 
regular outlines, relative position in 
a microscopical preparation, 30; 
transparent with curved outlines, 
relative position in microscopic pre- 
parations, 30; shading, 25. 
Objective, 1 ; achromatic, 3, 4 ; adjusta- 
ble, 5 ; adjustable, experiments, 22 ; 
adjustment for, 22 ; aerial image of, 
13 ; aperture of, 6, 7 ; aplanatic, 4 ; INDEX. 
95 
apochromatic, 4 ; back combination 
of, 3 ; cleaning back lens of, 27 ; col- 
lar, graduated for adjustment, 23 ; 
compound, 7; cloudiness or dust, 
how to determine, 30 ; dry, 4 ; equiv- 
alent focus of, 3 ; focusing for micro- 
spectroscope, 59 ; front combination 
of, 3 ; function of, 12, 13 ; high, focus- 
ing with, 18 ; homogeneous immer- 
sion, 4 ; homogeneous immersion, 
cleaning, 25 ; homogeneous immer- 
sion, experiments, 22, 24; immersion, 
4 ; index of refraction of medium in 
front of, 7 ; inverted, real image of, 
13 ; for laboratory microscope, 27, 
28 ; lettering, 3; of low and medi- 
um power, 4; low, focusing with, 
17; micrometer, 37; to use with 
micro-polariscope, 63 ; microscopic, 
3; to use with micro-spectroscope, 
59; for micro-spectroscope, focus- 
ing, 59 ; nomenclature of, 3 ; non- 
achromatic, 4 ; non-adjustable, 5 ; 
non-adj ustable, thickness of cover- 
glass for, table, 6 ; numbering, 3 ; 
oil-immersion, 4 ; putting in position 
and removing, 10; single-lens, 7 ; 
terminology of, 3 ; unadjustable, 5 ; 
water immersion, 24 ; water immer- 
sion, experiments, 22 ; working dis- 
tance of, 15. 
Oblique light, 16 ; with Abbe illuminat- 
or, 20 ; experiments, 19 ; with a mir- 
ror, 19. 
Ocular, 1 ; achromatic, 8; aplanatic, 8 ; 
binocular, 8 ; cloudiness, how to de- 
termine, 29 ; Campani’s, 8 ; compen- 
sating, 4, 9 ; compound, 8 ; deep, 8 ; 
designation by magnification or com- 
bined magnification and equivalent 
focus, 10; dust, how to determine, 
29; equivalent focus of, 10; erect- 
ing, 8 ; eye-point of, demonstration, 
14 ; field-lens, 8 ; focus, equivalent 
of, 10; function of, 13, 14; goniom- 
eter, 9; high, 5, 9; holosteric, 9 ; 
Huygenian, 9 ; Kellner’s, 9 ; letter- 
ing of, 10; low, 9 ; micrometer, 9, 
10, 42, 43 ; micrometer, micrometry 
with, 44 ; micrometer, putting in po- 
sition, 43 ; micrometer, valuation of, 
43 ; micrometer, varying valuation, 
44; micrometer, ways of using, 45 ; 
micrometric, 9; microscopic, 8, 9 ; 
negative, 8, 9 ; numbering, 10 ; or- 
thoscopic, 9, 12 ; par-focal, 18; peri- 
scopic, 9, 12; positive, 8, 9; projec- 
tion, 9 ; projection, designation of, 
10; putting in position and remov- 
ing, 10 ; Ramsden’s, 9 ; searching, 9 ; 
shallow, 9 ; solid, 9 ; spectral, 9, 10, 
54 ; spectroscopic, 9, 10, 54 ; stereo- 
scopic, 8; working, 9. 
Oil and air, appearances and distinguish- 
ing optically, 3r, 32. 
Oil-globules, with central illumination, 
31 ; with oblique illumination, 31, 32. 
Oil-immersion objectives, 4. 
Optic axis, 6 ; of condenser, or illumina- 
tor, 20 ; of microscope, 16. 
Optical, combination, x ; focus, 4 ; parts, 
1 ; parts of compound microscope, 
3 ; parts of microscope, care of, 26 ; 
section, 33. 
Order of procedure in mounting objects, 
dry or in air, 73 ; in Farrant’s solu- 
tion, 74; in glycerin, 73 ; in glycer- 
in jelly, 74; in resinous media by 
desiccation, 76 ; in resinous media by 
successive displacements, 76. 
Ordinary ray with polarizer, 63. 
Orthoscopic ocular, field with, 12. 
Outline, distinctness of, 32. 
Oxy-haemoglobin, 61. 
P 
Paper, bibulous, filter or Japanese, 12 
13 ; for cleaning oculars and obj ect 
ives, 26. 
Paraffin, removal from lenses, 27. 
Parfocal oculars, 18. 
Parts, optical and mechanical of micro- 
scope, 1. 
Pedesis, 34 ; compared with currents, 34; 
with polarizing microscope, 34; 
proof of reality, 35. 
Periscopic ocular, field with, 12. 
Permanganate of potash, absorption 
spectrum of, 60. 
Pin-hole diaphragm, 20. 
Photography, 4. 
Plane mirror, use of, 17. 
Pleochromism, 64, 65. 
Pleurasigma angulatum, 19. 
Point, axial, 6. 
Polarized light, 63 ; extraordinary and 
ordinary ray of, 63. 
Polarizer, 62 ; and analyzer, putting in 
position, 63. 
Polarizing microscope, pedesis with, 34. 
Position of objects or parts of same ob- 
ject, 30. 
Positive oculars, 8, 9. 
Potato, examination of, 35. 
Power of microscope, 36. 
Preparation of Canada balsam, Farrant’s 
solution, glycerin, glycerin jelly, 
82. 
Preparation of clearing mixture, liquid 
gelatin and shellac cement, 83. 
Presbyopia, effect on magnification, 40. 
Price of American and foreign micro- 
scope, 28. 
Principal focus, 1, 2, 3 ; focal distance, 3 ; 
point, 2. 96 
INDEX. 
Prism of Abbe camera lucida, 49-50; 
Amici, 54 ; comparison, 57 ; dispers- 
ing, 54 ; Nicol, 62 ; reflecting, 57 ; 
and slit of micro-spectroscope, mu- 
tual arrangement, 56. 
Projection ocular, 9; designation of, 10. 
Pumice stone for pedesis, 34. 
Pushing in draw-tube, 18. 
Putting on cover-glass, 74; an object 
under microscope, 11. 
Q-R 
Quinine, Herapath’s method of deter- 
mining minute quantities of, 85. 
Ray, chemical, 4 ; ordinary of polarized 
light, 63 ; extraordinary, 63. 
Real image, 1 ; inverted, 3. 
Reflected light, 15. 
Reflecting prism, 57. 
Refraction images, 25 ; index of medium 
in front of objective, 7. 
Refractive, doubly, 64 ; highly, 63 ; sin- 
gly, 64- 
Resinous media, mounting objects in, 
order of procedure, by drying or 
desiccation, 75 ; by series of dis- 
placements, 75, 76. 
Revolver, 11. 
Rice, examination of, 35. 
Rule or scale for magnification and mi- 
crometry, 37. 
s 
Scale, of magnification and micrometry, 
37 ; of wave lengths, 57. 
Scales of butterflies and moths, examin- 
ation of, 35. 
Screen of ground glass, 12, 13. 
Sealing cover-glass, 71, 72. 
Section, optical, 33 ; serial, 28, 78. 
Sediment in water, determination of 
character, 84. 
Selenite plate for polariscope, 65. 
Serial sections, 28; arranging and label- 
iug, 78; determining thickness of, 78. 
Shading object, 25; for micro-polari- 
scope, 35. 
Shellac cement, preparation of, 83 ; re- 
moval from lenses, 27. 
Sight, injury or improvement in micro- 
scopic work, 27. 
Silk, examination of, 35. 
Simple microscope, see under micro- 
1 scope. 
Slides, 66; cleaning, 66. 
Slips, 66. 
Slit mechanism of micro-spectroscope, 
54 ; adjusting and focusing, 56 ; slit 
and prism, mutual arrangement, 56. 
Solar spectrum or s. of sunlight, 54. 
Spectral, colors, 4; ocular, 10, 54. 
Spectroscope, direct vision, 54. 
Spectroscopic ocular, 10, 54. 
Spectrum, 4, 54. 
Spectrum, absorption, 54; amount of 
material necessary and its proper 
manipulation, 59, Angstrom and 
Stokes’ law of, 55 ; banded, not given 
by all colored objects, 61 ; of blood, 
60 ; of colored minerals, 62 ; of per- 
manganate of potash, 60. 
Spectrum, comparison, 57 ; complement- 
ary, 56 ; continuous, 54 ; double, 57 ; 
incandescence, 56 ; line, 54 ; of male- 
zeit sand, 62; single-banded, 61 ; 
solar, 54 ; two-banded, 61. 
Spherical aberration, 4 ; distortion, 3. 
Stage, mechanical, 28 ; micrometer, 37. 
Stand of microscope, 1 ; for laboratory 
microscope, 28. 
Standard distance (250 mm.) at which 
the virtual image is measured, 39. 
Starch, examination of, 35. 
Stokes and Angstrom’s law of absorp- 
tion spectra, 55. 
Swaying of image, 21. 
System, back, front, intermediate, of 
lenses, 3, 5. 
T 
Table of magnifications and valuation of 
ocular micrometer, 40; of tube- 
length and thickness of cover- 
glasses, 6. Of weights and measures 
(see inside of cover). 
Terminology of objectives, 3. 
Tester, cover-glass, 69. 
Textile fibers, examination of, 35. 
Thickness of cover-glass for non-adjust- 
able objectives, table, 6. 
Transmitted light, 16. 
Transparent objects having curved out- 
lines, relative position in micro- 
scopic preparations, 30. 
Triplet, achromatic, 2. 
Tripod, 2. 
Tube-length, 5 ; for cover-glass adjust- 
ment, 24 ; importance of, 24 ; micro- 
scopical, 5; of various opticians, 
table, 6. 
Turn-table, 71. 
U—Vw 
Unadjustable objectives, 5. 
Unit of measure in micrometry, 41. 
Valuation of ocular micrometer, 43. 
Varying ocular micrometer valuation, 44. 
Ward’s eye-shade. 27. 
Water immersion objective, 24. 
Water for immersion objectives, 24 ; re- 
moval, 26. 
Wave length, designation of, 58 ; scale 
of, 57- 
Weights and measures,see inside of cover. 
Wheat, examination of, 35. 
Wollaston’s camera lucida, 38, 48. 
Working distance of simple microscope 
or objective, 15.