THE BOOK OF THE MICROSCOPE By A. FREDERICK COLLINS THE BOOK OF THE MICROSCOPE THE BOOK OF WIRELESS TELEGRAPH AND TELEPHONE THE BOOK OF STARS THE BOOK OF MAGIC THE BOOK OF ELECTRICITY GAS, GASOLINE AND OIL ENGINES THE AMATEUR CHEMIST THE AMATEUR MECHANIC HOW TO FLY THE HOME HANDY BOOK KEEPING UP WITH YOUR MOTOR CAR MOTOR CAR STARTING AND LIGHTING THE BOOK OF THE MICROSCOPE BY A. FREDERICK COLLINS AUTHOR OF * ‘ THE BOOK OF STARS, ” “ THE BOOK OF WIRELESS TELEPHONE AND TELEGRAPH,” “THE BOOK OF MAGIC,” “THE BOOK OF ELECTRICITY,” “THE HOME HANDY BOOK,” “KEEPING UP WITH YOUR MOTOR CAR,” ETC- D. APPLETON AND COMPANY NEW YORK :: LONDON :: MCMXXIII COPYRIGHT, 1923, BY D. APPLETON AND COMPANY PRINTED IN THE UNITED STATES OF AMERICA A WORD TO YOU So this is The Booh of the Microscope! You are living not only in a world of three dimensions but in three worlds in one, though you may not realize it. These three worlds are (1) the world of the infinitely big and far away; (2) the world of ordinary sized things which is all around and about you, and (3) the world of the infinitely small, which is also at hand but hidden from your sight. The first of these three worlds is made up of the heavenly bodies and to see them to the best advantage you have to use a telescope; the second world is the one that you really live in and the things in it are of such magnitude you can see them with your naked eye, while the third and last world is formed of the most wonderful objects imaginable, but you must have a microscope with which to see them. It is this world of the infinitely small that I have told you about in this book, and it is ready and waiting for you to explore it. Wherever there is a barrel of rain-water, a pool, or a brook you will find microscopic speci- mens of plant and animal life galore and you V VI A WORD TO YOU have only to examine these with a microscope to see how fearfully and wonderfully they are made. Every plant and flower and tree that grows will take on a new meaning if you will look at them through a microscope. Animals of all kinds from the lowest form, called the Ameba, on up through the scale to the highest form, called man, make highly interesting and instructive objects for examination with a mi- croscope—but of course you can examine only a very small portion of these at a time. Then there is what is called the inorganic world—that is the rock and minerals and metals of which the earth’s crust is made and to ex- amine these under a microscope and learn about them is to gain an insight into nature that is in itself a liberal education. And, finally, there is the food, drink and household articles, such as fabrics and paper, that provide objects which you ought to examine with a microscope for the benefit and behoof of the health and the exchequer of your family. I have arranged the contents of this book so that if you will examine the objects in the order named you will have in the end a working knowledge of not only the microscope itself but the elementary principles as well of botany, zoology and histology and of the structure of the materials that make up the inorganic world. You do not need an expensive microscope A WORD TO YOU VII with which to explore the world of the infi- nitely small, for one costing ten dollars or less will do, though of course the better the instru- ment the more and the clearer you will he able to see. An inexpensive microscope can be bought of the L. E. Knott Apparatus Co., Bos- ton, Mass., or of the Palo Co., 90 Maiden Lane, New York City. Better instruments can also be bought from these firms and of the makers, Bausch & Lomb Optical Co., Rochester, N. Y., and the Spencer Lens Co., Buffalo, N. Y. You can buy any living plant or animal speci- men of the lower forms that I have described in this book, and dozens of others, of the Cam- bridge Botanical Supply Co., Waverly, Mass., Powers & Powers, Lincoln, Neb., and the New Jersey Entomological Co., South Amboy, N. J. As for the higher forms of plant and animal life you can buy specially prepared sections mounted on slides from the first named supply houses and all of them issue price lists and cat- alogues and you should by all means get copies of them. At any rate get a microscope and the rest will come in easy stages. A. Frederick Collins The Antlers Congers, New York CONTENTS CHAPTER PAGE I. What We Can See with a Micro- scope . K . .; ..... 1 II. Your Eye and the Action of Lenses 17 III. How the Compound Microscope Works . . 33 IV. How the Compound Microscope Is Made 49 V. The Right Way to Use a Micro- scope 63 YI. The Lighting of Microscopic Objects 78 VII. How to Collect Microscopic Objects 92 VIII. How to Dissect, Mount and Stain Objects 105 IX. Plant Specimens under the Microscope . w >•.... 120 X. Lowest Forms of Animal Speci- mens UNDER THE MICROSCOPE . 138 IX X CONTENTS CHAPTER PAGE XI. Higher Forms of Animal Speci- mens UNDER THE MICROSCOPE . 154 XII. Highest Forms of Animal Speci- mens UNDER THE MICROSCOPE . 169 XIII. Rock, Mineral and Metallic Specimens 189 XIV. Examination of Household Objects ........ 207 XV. Drawing, Measuring and Photo- graphing Microscopic Objects . 226 Index .. . . . . ... 235 LIST OF ILLUSTRATIONS PIGURH PAOH 1. Kinds of Magnifiers ..... 4 2A. Using the Microscope ..... 7 2. Kinds of Microscope 8 3. Section through the Human Eye . 19 4. Types of Lenses 21 5. Kinds of Rays of Light .... 22 6. How Light Is Refracted .... 23 7. How a Lens Forms a Real Image . 26 8. The Action of Lenses on Light . . 27 9. How Spherical Aberration Is Caused 30 10. How Chromatic Aberration Is Caused 31 11. How an Aplanatic Lens Is Made . 34 12. How Dispersion Is Neutralized by a System of Prisms 36 13. How an Achromatic Lens Is Made . 38 14. How a Compound Microscope Forms a Magnified Image 40 15. Shifting Effect Caused by a Cover Glass 45 XI XII ILLUSTRATIONS FIGOEB PAGE 16. The Principle of the Immersion Objective 47 17. Names of the Parts of a Good Microscope 51 18A. Achromatic Substage Condenser With Half Cutaway to Show Lens Combination 54 18B. The Iris Diaphragm 54 19A. The Coarse Adjustment .... 56 19B. How the Best Type of Fine Adjust- ment Is Constructed .... 57 20. How to Bemove an Objective . . 64 21. The Proper Way to Handle a Lens 67 22. The Correct Way to Use a Micro- scope ... 70 23. What Is Meant by Central or Axial Light 79 24. How to Tell When the Condenser Is Out of Center 88 25. How Oblique Light Is Obtained . > 89 26. Your Collecting Outfit .... 97 27. The Gathering Bottles . . . 98 28. Types of Dissecting Needles > . 101 29. Kinds of Life Slides . . ... > > 103 ILLUSTRATIONS XIII FIGURE PAGE 30. A Simple Dissecting Microscope Outfit 106 31. Kinds of Section Knives .... 107 32. How to Make a Simple Turn-Table . 114 33. How to Build up a Cell on a Slide . 115 34. How Cell Division Occurs in Palmo- glaea . : 122 35. How Conjugation Is Carried On . 123 36. A Diatom Under the Microscope . 125 37. The Sporange of Mucor Mucedo a Fungus 127 38. The Structure of a Typical Moss Plant 130 39. The Amoeba—A Unicelled Animal . 140 40. The Structure of a Sponge—A Sac- like Animal 143 41. The Hydra—A Plantlike Animal . 145 42. A Tooth of Echinus ..... 147 43. A Longitudinal Section of Worm of the Class Turbellaria .... 150 44. Arrangement of Teeth in the Palate of a Gastropod 156 45. Embryonic Stage of a Gastropod . 158 46. The Scale of a Butterfly .... 164 XIV ILLUSTRATIONS FIGURE PAGE 47. Hair of a Beetle Under the Micro- scope 165 48. The Spiracle of an Insect . . . 167 49. A Typical Bone Structure . . . 179 50. A Section Taken Through a Human Molar 180 51. A Longitudinal Section of an Animal Hair Showing Structure . . . 182 52. How the White and Red Corpuscles in the Blood of a Frog . . . 186 53A. How the Frog Slide is Made . . 187 53B. The Frog on the Slide .... 187 54. Circulation of Blood in a Frog’s Foot 188 55. Characteristic Systems in Crystal- lization of Minerals 195 56. How a Nicol Prism Polarizes and Suppresses Light Rays . . . 198 57. How Crossed Nicols Suppress Light 200 58. How An Anisotropic Body Acts Un- der Crossed Nicols 202 59. Interference Figures with Conver- gent Polarized Light .... 205 60. Some Vegetable Fibers . . . . 209 61. Some Animal Fibers . . . . . 210 ILLUSTRATIONS XV PIGDRB PAGE 62. Granules of Starch 216 63. How Parasites Appear Under the Microscope 222 64. Rod-Shape Tuberculosis Bacilli, Greatly Magnified 223 65. A Germ Incubator and a Colony of Germs 224 66. Preparing a Gelatine Culture . . 224 67. The Abbe Camera Lucida . . . 227 68. How the Camera Lucida Works . 228 69. How the Drawing Support Is Made 229 70. Beale’s Camera Lucida for Deter- mining Magnifying Power . . 231 71. A Photomicrographic Outfit . . 233 THE BOOK OF THE MICROSCOPE CHAPTER I WHAT WE CAN SEE WITH A MICROSCOPE As you probably know, the microscope (pro- nounced mi-Jcro-skop) is a lens, or a combina- tion of several lenses, which magnifies the images of objects that are (1) too small to be visible to the naked eye, or (2) whose details are so indistinct that they cannot be seen by the naked eye. The extent to which a microscope will magnify depends on several factors and these will be explained in good time. The Invention of the Microscope.—Like all other scientific instruments, the microscope has passed through a long period of development, and it is hard to believe that the compound mi- croscope as we know it to-day is the outcome of the flea glass which was in use when Columbus set sail on his first voyage of discovery. The Flea Glass.—The flea glass,1 which was a simple convex lens, was so called because the iThe Latin name for the flea glass was vitra pulicaria, which sounded better. 1 2 BOOK OF THE MICROSCOPE intellectual giants of those latter medieval days used it to observe such small insects as the flea, the louse, and the mite. When they saw the enlarged images of these innocent parasitic creatures of man and beast, and found they were such terrible looking objects, they were scared almost out of their senses. The flea glass had a magnifying power of from six to ten times, and it is well for those who used it that it was not higher. The Compound Microscope.—Two or more lenses were first used together some time be- tween 1590 and 1609; this was done independ- ently by Hans and Zachias Jansson (father and son) who were Dutch spectacle makers, and Galileo, the greatest scientist of his time. These early compound microscopes had a dou- ble convex lens for the object glass and another like lens for the eyepiece. These lenses were mounted in a tube more than a foot long and in this crude state the mi- croscope remained until the end of the eigh- teenth century. In the beginning of the nine- teenth century, however, there was a fresh out- burst of enthusiasm concerning things scien- tific, and the microscope has been constantly improved upon ever since, until now it is one of the most highly developed and valuable instruments in the service of mankind. WHAT WE CAN SEE 3 The Kind of Microscope You Want.—From what you have just read you have gathered that as far hack as Galileo’s time there have been two kinds of microscopes: (a) the simple magnifying glass, or magnifier, as it is called, and (b) the compound microscope; both kinds are in use at the present time. There are, however, several modifications of these, and the kind you want depends on what you want to see and do with it. A magnifier will be found useful for obtaining magnifica- tions of the image of an object of from four to twenty-five times, while for higher powers you will need a compound microscope; this will give you a magnified image of the object of from 25 to 1,000,000 times. What You Can See with a Magnifier.—Any kind of a convex lens will serve as a magnifier, but a lens made especially for the purpose is better because you can see the object more clearly and there is less distortion. Take any kind of a magnifier and look at the printed let- ters on this page and you will at once be struck with the fact that they are greatly enlarged and stand out very boldly; but you will also see that, instead of their edges being sharp and clear cut as they appear to the naked eye, they are rough and uneven. Then examine the paper and you will observe that it is not at all as smooth as your naked eye 4 BOOK OF, THE MICROSCOPE would have you believe, but instead is very coarse. A most striking example of the en- larging power of a magnifier is to look at the skin of your hand with one, especially the cuti- cle around your finger nails, and you will be A-Reading Lens C-Tripod Mag- nifier D-Doublet Maqnifier B- Linen Tester Fig. 1.—Kinds of Magnifiers surprised, and probably shocked, to see the condition in which it is. This done, take a look, like the learned man of old, at a flea, an ant, or any other minute animal and you will see why the ancient ob- servers were amazed and described the flea in terms that threw the prehistoric plesiosaurus 2 and modern sea serpent in the shade. And so also with nearly every object you examine. A lens with a magnifying power of only four 2 A long-necked marine reptile of the dim long ago. WHAT WE CAN SEE 5 times will reveal a strange and wonderful world about you that you would scarcely imagine ex- isted. Nor is a magnifier an instrument intended merely for pleasure—no, indeed, for it is use- ful, and often indispensable, in many and diverse ways. So useful, in fact, is it that it is made for special purposes, as for instance the reading glass as shown at A in Fig. 1, which enables people with dimmed eyesight to read printed text and handwriting, while sleuths of the Sherlock Holmes variety employ it for ex- amining fingerprints, tracks of man and beast, and other details too small for the naked eye to see. Then there is a little magnifier called a linen tester (see B in Fig. 1) which was originally used for counting the threads of fabrics, but which is now employed for all manner of pur- poses where a low power will suffice. Another magnifier (see C in Fig. 1) consists of a double lens and is known as a tripod magnifier. It has a magnifying power of seven or eight times; this is enough for elementary school work, such as examining seeds and making similar obser- vations. A more powerful glass is the doublet magnifier, shown at D, its magnifying power ranges from six to 24 times. The great advan- tage of a doublet is that it gives excellent defini- 6 BOOK OF, THE MICROSCOPE tion and an exceptionally flat field with a long focal length. A magnifier is also useful in examining the works of watches, the condition of jewelry, especially the mountings, and also of gems; any imperfections in the latter such as flaws, cracks, etc., are immediately discernible through a magnifier when to the naked eye they appear quite perfect. In almost every line of business and in nearly every industry the magnifier in one form or another is used as a tool of trade. In the beginning of the text under the present caption I suggested that you should examine your nails with a magnifier, I will add here that it is equally as serviceable in examining the eyes, the teeth and the throat. It is a won- derful aid in locating foreign particles in the eye. The lower the power of the magnifier the easier it will be to find the offending particle, provided it is large enough to be readily seen; conversely, the higher the power of the magni- fier the harder it will be to find it, but once hav- ing found it the better you can see it. What You Can See with a Microscope.—After you have used a magnifier for awhile and then change over to a compound microscope (A and B), you will have another surprise in store, for instead of seeing the image of an object magni- fied a few times, you will see it magnified a hun- dred, a thousand, or a million times according WHAT WE CAN SEE 7 to the power of your instrument. This being true, you cannot look at an object as large as a flea all at once, but you have to examine it piece- meal, that is, a small portion of it at a time. A- A Cheap Microscope Magnifies UOTimes Fig 2A.—Using the Microscope Suppose you want to learn the mechanism of the different parts of a cricket or a fly, or a flea. The first thing you have to do is to dissect it, that is, you cut it up very carefully and take the part of its anatomy you want to learn about, say the gizzard of the first, the proboscis of the second, and the pygidium? of the last, mount it 3 This is the last, or posterior, dorsal segment. 8 BOOK OF THE MICROSCOPE and then study it under the best possible con- ditions of light and power. Home Uses of the Microscope.—What I have just told you about examining the parts of little animals with a compound microscope was in- B-An Up-to-Date Microscope Magnifies 50,000 Times Fig. 2B.—Compound Microscope tended to bring out the difference in the power of the former instrument and that of the mag- nifier, for there are many other branches of microscopy (pronounced mi-hros'-kop-y) that are just as important, if not more so, for in- stance, the examination of everyday substances. If every home had a compound microscope WHAT WE CAN SEE 9 in it, there would be far less sickness than there is now, for the two chief things which derange the human organism are (1) impure water, and (2) impure food. The constant use of a wide variety of these essential to life has made us careless as to their condition and quality, but since disease often lurks in them it behooves all of us to combat it by the simple and highly interesting expedient of making a microscopic examination of them. Then there is the matter of fabrics. With a very low power microscope you can see exactly what kind of fibers a piece of goods is made of and how it is made. It may be all wool and have the proper feel, and look all right to the naked eye, but it makes a very considerable difference in the wear of it whether it is made of short or long fibers and this the microscope will quickly show. Again, since artificial silks have come into common use, it is well to know whether you are getting the fiber produced by the silkworm or that manufactured from cellulose. Educational Uses of the Microscope.—While it is a source of much pleasure, and you can also learn considerable about the structure of plants and animals, or biology, as these two branches of science when combined are called, by examining them haphazard with a micro- scope as you come to them, it is a far better 10 BOOK OF THE MICROSCOPE plan to do so in a systematic way, for then yon will get what might be called a working knowledge of these great and far-reaching subjects that will be of real educational value. The Examination of Plants.—That branch of biology which treats of plant life is called bot- any, and the easiest and best way to learn how various plants are built up is to begin with one of the Algae (plural of Alga), which are among the lowest forms of plant life. They are some- times incorrectly called “frog-spittle.” Hav- ing discovered the nature of the algal structure, that is, how the algae are built up, you go on to the next higher forms which are the Fungi (plural of Fungus) to which group the mush- rooms belong. Then you take up the mosses, or Musci, to give them their scientific name, next the ferns, or Filicales and follow this with an examina- tion of the family of pine tree, or Gymnos- permae, which wrere the first real trees that ap- peared on the earth’s surface. Finally, you examine the flowering plants and all of the flowering trees or Angiospermae, which con- stitute the highest form of plant life. An examination of the leaves, the buds, the pollen, the stamens and the cross sections of these plants will fix in your mind for all time the difference between them, and in another WHAT WE CAN SEE 11 chapter I will tell yon how to prepare and ex- amine each one in order. The Examination of Animals.—After you have made a microscopic examination of the different groups of plants, you can then take up the various groups of animals, or zoology, as it is called, and learn how the several parts of them are built up. This you can do by start- ing with the Amoeba and going on up step by step to, and including, man, which is the most complex of all the life forms. Just as the Algae are among the lowest forms of plant life, so the Amoeba is one of the lowest forms of animal life, and belongs to the phylum, called Protozoa. After you have studied it with your microscope you take a higher form, the sponge, which is a member of the phylum, Porifera. Next you look into the structure of the Hydra, of the phylum, Coelenterata; then into flat, round and true worms of the phyla: Platyhelminthes, Nemathelminthes and Anne- lida, and this will bring you to the highly inter- esting Arthropoda phylum, which includes the insects such as moths, butterflies, and beetles. Having learned the nature of the structure of these you are ready to begin your examination of the highest order of animals which go by the family name of Chordata (pronounced cor- da-ta) and which includes all of the animals that have notochords and backbones. It is in 12 BOOK OF THE MICROSCOPE these latter examinations with the microscope that yon see how the nerves, muscles, brain, blood, heart, lungs, liver, stomach and kidneys are built up of cells, all of which is wonderfully fascinating work. Technical Uses of the Microscope.—While you can study all of the foregoing objects with an $8 or $10 microscope, a better one will nat- urally give you a higher magnification and a clearer field. But if you are going to be a real microscopist (pronounced mi-kros-ko-pist) and do technical work, you must have a good high power instrument and this will cost you from $25 up to $250, depending very largely on the state of your finances and the class of work you are going to do. The Microscope in Health and Disease.— During the latter part of 1600 the microscope had been sufficiently improved so that micro- scopists began to find out how plants and ani- mals were built up. Leeuwenhoek, a Dutch in- vestigator, made a microscope, and with it he discovered that there were enormous numbers of minute living things in the saliva of the mouth, in water and in matter that was decom- posing. He called these microscopic forms of life animalcules and these have since been given the name of bacteria ,4 and are the very lowest forms of plant life. 4 The singular of which is bacterium. WHAT WE CAN SEE 13 Hooke, a botanist of England, found that cork was composed of minute cells, and follow- ing came Malpighi and Swammerdam who ob- served that insects also had a cellular structure. In the early part of the nineteenth century the microscope was greatly improved upon and with it Schleiden and Schwann were enabled to work out the theory that all plants and ani- mals are built up of microscopic particles of liv- ing matter called cells. Then Leeuwenhoeck’s animalcules were studied with the higher power microscopes that had been devised, but it was not until the eighties of the nineteenth century that Koch and Pasteur founded the science of bacteri- ology. The bacteria are one-celled plants that multiply by division; some of them are helpful to man and others are very harmful. The good little bacteria are simply scavengers that live upon dead matter while others are parasites and consume the living flesh of the higher ani- mals. In doing this they give off poisonous matter which in turn produces diseases of various kinds. The Microscope as a Legal Aid.—I have previously mentioned that the magnifier serves as an aid in the investigations of the detective and often plays an important part in determin- ing some mooted legal point. One of its uses is in finding the direction a bullet took when it 14 BOOK OF THE MICROSCOPE was fired and the distance from which it was fired, both of which are obtained by examining the wound. Other details concerning the bullet and powder that were used are revealed by the microscope. As a supplemental aid to the Bertillon sys- tem? of measurements, the microscope is used to identify criminals and others by means of impressions left by the fingers. The ridges and furrows on the finger tips remain the same all through life, nor can they be changed by any known means. The microscope is also largely used in determining whether or not a signature or other writing is a forgery. Finally it is often used to prove whether blood stains are those of a human being or of some lower animal. The Microscope in Chemistry.—The use of the microscope in chemistry, or microchemis- try, as it is called, has not been very extensive in time past, but the value of it in the study of crystals is well known; it is also being applied to the study of reactions and chemical analysis. The formation of crystals in a solution can be observed while the process is going on and the minute crystals thus produced in many solu- tions often show the most remarkable charac- teristics. 5 This is a system of measurements and records thereof of man and includes personal characteristics. It is used as a means of identification. WHAT WE CAN SEE 15 The advantage of using the microscope for observing the change in the condition of chemi- cal reactions is that (1) only a very minute amount of the substance, or substances, need be used; (2) the ease with which the substances are prepared—it is only necessary to place a drop on a slide; (3) the short time required for the operation; and (4) the small amount of ap- paratus necessary to work with. The Microscopic Study of Minerals and Metals.—There are numerous tests used to identify minerals, but the best way is to exam- ine them with the microscope. To examine a mineral it must be cut into slices sufficiently thin so that the light will pass through it and then every detail of its structure can be clearly seen when it is illuminated by refracted light. This forms a more simple means of identifica- tion than chemical analysis. The study of min- erals with the microscope is called petro- graphy.9 The microscope is also used extensively in the industries for examining the structure of metals and their alloys, and hence this branch of microscopy is called metallography.'1 In making these examinations the metal is pol- ished and the surface is obsered by reflected 6 Protrology is the science of rocks and petrography is that branch of protology which includes the minerological and chemical characteristics of rocks. 7 The science that treats of metallic substances. 16 BOOK OF, THE MICROSCOPE light. The microscope not only shows the structure of various metals and alloys, but also whatever impurities there may be in them. The hardness of steel can easily be learned with the microscope as its hardness depends on the amount of carbon in it. CHAPTER II YOUK EYE AND THE ACTION OF LENSES Nearly all of the gifts which nature has be- stowed upon us are so familiar, by virtue of the fact that we have them with us from the time we are born, that we are too often prone to con- sider them as mere commonplaces, and hence seldom take the trouble to investigate them. The greatest of these, and the one to which we give, as a rule, the least thought and attention, is light, and which, as you will see shortly, is of the greatest importance in the needs of our everyday lives. Light, the Essential of Life.—The chief source of light to which the earth, and all that is in and on it, owes its very existence, is our sun. This gigantic luminary, although it is 93,000,000 miles away from us, sends out its light and heat waves through the ether,1 and these travel at the rate of about 186,000 miles a sec- 1 The ether is an elastic medium that fills all of the spaces in the universe which are not otherwise occupied by gross matter. It is by, in and through the ether that light and all other electromagnetic waves and disturbances are set up and transmitted. 17 18 BOOK OF THE MICROSCOPE ond. Without light and heat the earth would be enveloped in absolute darkness and it would be intensely cold—so cold that life in any form could not exist, much less thrive, on it. Light is not only an essential of life but it also provides us with the connecting medium between objects and our eyes so that we can see them. This ability of our eyes to sense the size, shape, color and distance of external ob- jects is called sight, and it is this particular phase of the action of light on our organs of sight in which we1 are interested in just now. Light, Sight and Your Eye.—The ancient philosophers knew that light traveled in straight lines, but what they did not know is that the eye is able to see some objects by the light they set up and other objects by the light that is reflected by them. It was centuries later that the way light really acts and the eye really sees was learned, and as these have to do with the use of the microscope it is useful to get them clearly in your mind. Your Eye, the Organ of Sight.—Now, al- though the eye itself is a complicated piece of mechanism, it is easy to understand how it works when it sees things, for it is made very much like a little camera. If you will take a look at Figure 3, which is a cross section through the human eye, you will see that the THE EYE AND LENSES 19 chief parts of it are formed of (a) the cornea, (b) the iris, (c) the lens, and (d) the retina. The cornea is a tough, transparent film that protects the iris and the lens, and it fits over these as a crystal fits over the face of a watch. The iris, which is formed of a thin membrane with a hole in it, corresponds to the diaphragm Iris The Optic Nerve The Lens Cornea Pupil The Retina or Screen Iris Pig. 3.—Section through the Human Eye of a camera and its purpose is to let in the exact amount of light that is best suited to its needs. The hole in the iris forms the pupil; this is automatically made larger or smaller according to the amount of light the eye needs. The lens of the eye is doubly convex, and is like that of a camera. It is through, and by means of it that the rays of light of an object are brought together and thrown upon the retina, which is a sensitive screen at the back of the eye. When the rays of light from the 20 BOOK OF THE MICROSCOPE object pass through the lens they are focused on the retina and in this way a picture of the object is formed on it. The optic nerve, which is connected with the retina, leads to the brain, and as the rays of light fall on the retina they set up a photochemical reaction, something like that which is set up on a camera film. This re- action gives rise to the nervous impulse which then travels over the optic nerve to the brain, where the object is visualized, or as we say it in everyday language, we see it. Since your eye, with which you see, is made up of a lens as one of its chief parts, it is both fitting and proper that you should examine into the action of light as it passes through a corn vex lens as well as other kinds of lenses. More- over, there are a large number of instruments which are used to aid the natural lens in the eye and which produce an enlarged image of an object or enable us to see it more distinctly and these are all formed of one or more lenses. Various Kinds of Lenses.—Every one is familiar with the most common kind of lens which is known as a magnifying glass; this is a double convex lens like that of the eye. Besides this there are several other kinds of lenses, all of which are shown in Figure 4. Lenses can be divided into two general groups (a) convex lenses, and (b) concave lenses. Named in their usual order the various lenses are (1) the THE EYE AND LENSES 21 double convex, (2) the plano-convex, and (3) the converging meniscusd All of these lenses have at least one surface which curves outward. Then there are (4) the double concave, (5) the plano-concave, and (6) the diverging meniscus. And all of these have at least one surface which curves inward. Convex Lenses Concave Lenses Optical Axis Double Convex 2 Plano Convex 3' Converging Meniscus Ai Double Concave 5 Plano Concave & OVverging Meniscus Fig. 4.—Types op Lenses While all of these lenses are largely used in the construction of various optical instruments to enable the eye to see the better, the chief one that concerns us in microscopy is the double- convex lens. To understand how the micro- scope forms enlarged images of objects you must know how a ray of light acts in passing through a convex lens. Once that you get this clear in your mind you will have the basic prin- ciple of the whole thing in a nutshell. Kinds of Rays of Light.—Before going into the effect a lens has on a ray of light when pass- ing through it, let us find out a little more about 22 BOOK OF THE MICROSCOPE light itself. First of all there are two ways in which rays of light may travel through space and these are (1) as parallel rays, such as are given off by the sun, and (2) as divergent rays, such as are given off by a lamp, or any small and close source of illumination. These differ- ent kinds of rays are shown at A and B in Fig- ure 5. The Sun Flame Candle A- Parallel Rays ot Light B-Divergent Rays of Light Fig. 5.—Kinds of Kays of Light A large number of rays of either kind is called a beam, or a pencil, of light; when this passes through a double convex lens both paral- lel and divergent rays are affected in the same way, that is, they are bent out of their original direction, and this bending, or refraction, of the rays, as it is called, takes place downward toward the center of the optic axis.2 To see just how and why this happens, let us take the case of a single ray of light passing through a prism, since a double convex lens acts 2 This is a line drawn through the center of a lens and at right angles to its diameter as shown in Fig. 4. THE EYE AND LENSES 23 much in the same way as though it were formed of two prisms with their bases cemented to- gether as shown at A in Figure 6. How a Prism Refracts Light.—A ray of light is made up of light waves and these move in the same direction as the ray. A ray is formed of transverse vibrations in the ether, or light Company irr Column of Fours Together VP** A Refract- ing Angle Ro*-<* Refract- ed Ray Plowed Field B Prism kC B-Analoque \ of the Refract- ion of Light Ray of Light C-How Light Passes I hrough a Prism Pig. 6.—How Light Is Kefracted waves, as they are called, and they are parallel with each other so that their fronts are at right angles to the ray. Thus the ray of light may be thought of as a company of soldiers march- ing in a column of fours as shown at B. If such a column were to march from a smooth road into a roughly plowed field, the soldiers, as they entered the field one by one, would be slowed down, or retarded, and as a re- 24 BOOK OF THE MICROSCOPE suit of this slowing down the column would exe- cute a nearly perfect half-right face. Upon emerging from the field just the opposite action would take place and the soldiers on reaching the smooth road would speed up, or he acceler- ated, with the net result that the direction of the march would again be bent, all of which is closely shown at B. A ray of light with its perpendicular waves passing from the air into a prism, as shown at C, will be bent, and for the same reason, as ex- plained above in connection with the soldier analogue, as it advances into, or emerges from, the prism. This bending of the ray out of its straight course is called refraction; it is this property of a lens that enables it to form images of objects on the retina of the eye or on any other suitable screen. Real and Virtual Images.—An image of an object is a picture of it and this may be either (1) a real image, or (2) a virtual image. The difference between these two kinds of images is that a real image will project a picture on a screen while a virtual image will not. In other words, a virtual image is one that the eye sees as if it really existed but which as a matter of fact does not exist. To project a real image on a screen all you need to do is to hold a convex lens close to a sheet of white paper, or, better, white card- THE EYE AND LENSES 25 board, and in a line with the object, to serve as a screen on which to catch the image. By moving the lens to and from the white surface yon will be able to obtain a sharp picture, or image, of the object. This process is called fo- cusing. Moreover, yon will observe that this image is inverted, that is, it is upside down on the sur- face which is now called a screen. This is be- cause the rays of light from the object in pass- ing through the lens are refracted so that those from the top of the object after emerging from the lens are bent downward, cross the optical axis and are projected at the bottom of the screen. Likewise those rays that come from the bot- tom of the object are bent upward and appear at the top of the screen. Those rays that come from the middle of the object and which pass through the center of the lens are not bent, or refracted, because the light waves of which the ray is composed are not slowed down on enter- ing and leaving the lens. How a lens forms a real image is shown in Figure 7. The Focus of a Lens.—When parallel rays of light, as those from the sun, pass through a con- vex lens they are refracted and cross at a point on the optic axis. This point is known as the principal focus (see A in Figure 8); it is the point at which the sun’s rays are the hottest 26 BOOK OF THE MICROSCOPE when a convex lens is used as a burning glass. It is clear that with a double convex lens there can be a principal focus on either side of it, and this depends on which side the source of light is. The distance of either of the princi- pal foci3 from the center of the lens is known as Parallel Rays of Light ,Lens v TS 'O' i. <0 £ c*_£ Object the focal length; this can easily be determined by using it as a burning glass. How the Focus Affects the Image.—Now the principal focus of a lens and the relative posi- tion of the object to the former is of great im- portance in the formation of the images. You have just seen how, at A, in Figure 8, parallel rays, when they pass through a lens, converge and meet at a point. On the other hand, if an object is placed at this point, or principal focus, the rays from the object will, upon emerging from the lens, be parallel and, consequently, will not focus; this is likewise shown at A. What occurs when an object is placed beyond the principal focus of a lens is that the rays are Pig. 7.—How a Lens Forms a Real Image 3 Plural of focus. THE EYE AND LENSES 27 brought to a focus beyond the principal focus as shown at B, on the other side of the lens. The nearer the object is brought to the prin- Parallel Rays of Refracted Light v' A Lens Optic Axis Object Converging Rays of Refracted Light Vens •o^ B Optic Axis 'Conjugate Focus Conjugate Focus Object c Virtual Con'juqate Focus 3 W\v,et<'&C/ Magnified Upright Virtual — Image Optic Axis ..A E Principal Focus B SdVirtua! Conjugate Focus C-The Formation of a. Virtual Image Pig. 8.—The Action of Lenses on Light cipal focus the farther away will be the point at which it focuses on the other side of the lens, and, as you have just seen, when the object is placed at the principal focus the rays are never brought to a focus on the other side, since they 28 BOOK OF THE MICROSCOPE emerge as parallel rays. From this you will gather that there must be two points on the optical axis of a lens so that if the object is at one point the focus will be at the other point. These two points are called the conjugate foci of the lens. How to Find the Focal Length of a Lens.—If the object is placed at a distance from the prin- cipal focus which is equal to the focal length of the lens (in other words, at a distance of twice the focal length from the lens), then its conju- gate foci will be twice the focal length from the lens on the other side. Thus, when the image and the object are equidistant on either side of the lens, they must be equal to each other in size and four times the focal length of the lens apart. The above fact is very useful in determining more accurately than the way I previously told you to use in finding the focal length of a lens. To do so by this method place the object in front of the lens with the screen back of it and adjust the position of the object and the screen until the image and the object are of the same size. Then measure the distance of the object from the screen and divide it by four; this will give the focal length with a fair degree of accu- racy. How Virtual Images Are Formed.—I have already explained how a real image is formed THE EYE AND LENSES 29 and how it can be thrown on a screen. If, how- ever, the object is placed between the lens and its principal focus the rays emerging from the other side of the lens will be divergent, as shown at C, and, hence, can never meet in a focus on that side of the lens. But if these divergent rays are traced back- ward as shown by the dotted lines, it will be found that they come to a focus somewhere back of the principal focus of the lens and, conse- quently, on the same side of the lens as the object. This point is called the virtual conju- gate focus of the lens. Now place your eye in the vicinity of the divergent rays at e and / when they are converged by the lens of the eye and brought to a focal point on the retina. You will then see the enlarged image c and d of the object a and b. To prove that this is a virtual image all you need to do is to place a screen where your eye was when you saw the image and you will find that the image will not be thrown on the screen. Farther, you will readily see from the diagram why a virtual image is an upright and not an inverted image as is a real image. Having firmly grounded the above principles in your mind, for they are the fundamentals of optics, let us next consider two defects which crop out in the use of lenses for aiding the eye; namely, 30 BOOK OF THE MICROSCOPE (1) spherical aberration, and (2) chromatic aberration. What Spherical Aberration Means.—While it is true that all of the rays of light in passing through a lens are refracted to nearly the same degree, nevertheless, there is just enough dif- ference in the degree of refraction of each ray to cause them to meet at various points along the optical axis instead of at a single focal point on it. X# Parallel Rays • o+ Light Refracted Rays Parallel Rays of Light A B Fig. 9.—How Spherical Aberration Is Caused This difference is known as spherical aberra- tion, and in working with a microscope it is very annoying, as it prevents yon from getting an absolutely sharp focus, which of course is nec- essary to clear vision and accurate observa- tions. How spherical aberration occurs when parallel rays of light strike first the flat and then the curved surface of a plano-convex lens is shown at A and B in Figure 9. From these diagrams you will observe that the aberration is greatest when the light strikes the flat side first, and least when it strikes the curved side THE EYE AND LENSES 31 first. From this you will see that the amount of spherical aberration is due to the shape of the lens, and it follows that it is least in a dou- ble concave lens. What Chromatic Aberration Means.—White light, such as the light from the sun, may be broken up, by passing it through a prism into seven different colors which, when blended to- gether, act on the retina of the eye and give us through the optic nerve the sensation of white Ray of White Light S*cL+. y Versed p, Optic Axis Fig. 10.—How Chromatic Aberration Is Caused light. These different colors are known as the colors of the spectrum; named in order they are violet, indigo, blue, green, yellow, orange and red. In passing through any kind of a lens it so happens that the two extremes of the spectrum —violet and red—are refracted unequally and therefore are bent in different directions. This causes the ray of white light to be split up, or dispersed, into its component colors (since the intermediate colors are also refracted un- 32 BOOK OF THE MICROSCOPE equally), and in this way the image is again thrown out of focus and made indistinct. In this case, though, there is an additional evil, for the blurred edges of the image take on all of the colors of the spectrum. Figure 10 shows how chromatic aberration is caused by a double convex lens. It is clear that the very purpose of the microscope would be defeated if some means had not been found to correct the spherical and chromatic aberration of the lenses. The corrective methods employed will be explained in the following chapter. CHAPTER HI HOW THE COMPOUND MICROSCOPE WORKS Yon have seen how a magnifier is made and how it works; the next step is to take np the compound microscope, find how it is con- structed, learn what its optical properties are, and especially about the action of light which, in passing through it, forms the highly enlarged image of the object under examination. From the last chapter you learned that ordi- nary convex lenses have two serious inherent defects which, if they could not be counteracted, would prevent them from being used for high power microscopic work; these are spherical and chromatic aberration. Now, before going into the action of the compound microscope, you should know how these defects are reme- died so that the instrument will give a clear and sharp definition. How Spherical Aberration Is Corrected.— Spherical aberration, as you know, is caused entirely by the shape of the lens, and, further, as was shown in Chapter II, it is least in a double concave lens. With a demand for lenses 33 34 BOOK OF THE MICROSCOPE in which this defect is obviated, or at least re- duced to the smallest possible amount, lens- makers set to work to overcome it. Finally it was discovered that a lens could be made in which the amount of spherical aberration was reduced to an almost negligible quantity. Parallel Pays of Light Radius 6"~ Radius*! Principal Focus Pig. 11.—How an Aplanatic Lens Is Made This was done by grinding the lens so that the curvature of the two surfaces, or faces, as they are called, is unequal, one being considerably more convex than the other. The point at which spherical observation is reduced to a minimum occurs when the radii1 of curvature i Plural of radius. HOW THE COMPOUND WORKS 35 are in the proportion, or ratio, of six to one; this is clearly shown in Figure 11. It must be borne in mind, however, that this holds good only when the more curved surface is nearest the object to be examined, for when the other side is turned toward it the spherical aberra- tion then nearly reaches a maximum. A lens corrected for spherical aberration in this fashion is known as an aplanatic lens. How Chromatic Aberration Is Corrected.— The natural dispersion, or splitting up, of white light by a lens, and the unequal bending, or re- fraction, of its component colors,2 is due to two things: (1) the kind, or nature, of the glass of which the lens is made; and (2) the refracting angle of the lens. For the purpose of making this clear let us again take the case of white light passing through a prism, since the action of the prism on light passing through it is more apparent than that of a lens, although the principle is identical. By referring to B in Figure 6 you will note that the angle B-A-C is known as the refracting angle. This angle determines the amount, or degree, to which the rays of light passing through the prism will be reflected. If, now, two prisms are made of the same kind of glass and have the same refracting angle, in 2 These are found by the difference in the wave lengths that make up the ray. 36 BOOK OF THE MICROSCOPE other words, if two prisms that are exactly alike are placed side by side, one being set in an in- verted position, the dispersive power of the first prism will be exactly counteracted, or neu- tralized, by the second prism, because that of the second prism is equal to and opposite that of the first one. Figure 12 shows precisely how this is done. Incident Roy Dispersed Rays Emergent Ray Recomposed Fig. 12.—How Dispersion Is Neutralized by a System op Prisms On the other hand, you will see from Figure 12 that not only is the dispersive action of the first prism reversed but that its refractive power is also neutralized by the second prism, since the ray of light which finally emerges from it is parallel to the ray of light that enters the first prism. For this reason in such a sys- tem of prisms, although the evil is done away with, refraction—that property of prisms and lenses which makes the formation of images possible—is also done away with, or, rather, its effect is neutralized. This makes this scheme of itself of no practical use in the construction of instruments. Fortunately for the optical inventor his re- sources were not entirely exhausted when he HOW THE COMPOUND WORKS 37 reached this point for he had learned that prisms made of different kinds of glass have different dispersive powers. In particular he had learned that a prism composed of a certain kind of glass known as flint glass has twice the dispersive power of one made of the kind known as crown glass, while their refractive powers are practically the same. Further it was known that a prism having a refracting angle of given size would have twice the refractive power of a prism having one-half as large a refracting angle, and that if the latter were made of a glass having twice the disper- sive power of the first, the dispersive power of both prisms would be the same, since the power of dispersion varies with the angle of refrac- tion. With these facts to work upon the solu- tion of the problem soon resolved itself down to the following method: A system of two prisms is arranged as shown in Figure 12. The first prism, however, is made of crown glass which has only half the disper- sive power of the second prism which is made of flint glass. Further, the first prism is given a refracting angle twice as great as that of the second. As a result of this combination, which acts in accordance with the principles outlined above, dispersion is entirely destroyed because that of the second prism is equal and opposite in nature to that of the first. The second 38 BOOK OF THE MICROSCOPE prism, however, having a smaller refracting angle will not neutralize all of the refraction set up by the first prism and, consequently, it Will be possible for an image to be formed. What the Achromatic Lense Is.—Now, since the same principles which apply to prisms also apply equally to lenses, a lens may be corrected for chromatic aberration in the same manner as described for the prism and such a lens is Plano-Concave Lens Double Convex Lens of Crown Glass Fig. 13.—How an Achromatic Lens Is Made known as an achromatic lens. The correction is accomplished like this: a double convex lens of crown glass is fitted into a plano-concave lens of flint glass and their opposite curvatures are adjusted so that the flint glass compen- sates for all of the dispersion caused by the crown glass lens, but at the same time it neu- tralizes only half of the refraction caused by the crown glass. It should be noted here that lenses made of flint and crown glass as described above are not only achromatic but also tend to be aplan- atic, that is, they tend to decrease the amount HOW THE COMPOUND WORKS 39 of spherical aberration as well as to eliminate chromatic aberration. A cross section of the achromatic lens is pictured in Figure 13. Hav- ing seen how the inherent defects of lenses are corrected so that they can he used for high power microscopic work you are now ready to take up the compound microscope and learn how it produces such a tremendous magnifica- tion of an object which may be invisible to the eye even when this is aided by ordinary lenses. The Lenses of the Compound Microscope.— In its simplest form the compound microscope consists of (1) an objective lens, or objective, as it is called for short; this is a double convex lens, and is called an objective because through it the rays of light from the object first pass; (2) this objective is mounted in a tube, the pur- pose of which is to exclude from the eye all rays of light except those passing through the ob- jective from the object; (3) in the other end of this tube is mounted another and shorter tube which has fixed in it (4) the ocular, or eyepiece, which can be moved toward or away from the objective, all of which is shown in A in Figure 14. It is through the ocular that the magnified image formed by the objective is viewed by your eye and it is by the former that the image is still more highly magnified. In order that the object may be made sufficiently luminous so that 40 BOOK OF THE MICROSCOPE it can be clearly and distinctly seen, there is (5) a mirror placed under it, or a mirror or -Real Inverted Image Formed on Retina. The Eye .Lens of Eye . Ocular* Eye piece Magnified Real Inverted Image Formed by Objective £; Highly Mag- nified Upright ~and Vertual Image Formed by tneOcular F Refracted rays of Light Objective fl Principal Focus Object Incident Rays o-f Light ' Reflected ravs of liaht 7 Fio. 14.—How a Compound Microscope Forms a Magnified Image Mirror a lense above it, which throws the rays from some source of light upon it. In the first case the light is reflected by the mirror and passes through or to the object to be exam- HOW THE COMPOUND WORKS 41 ined, and in the latter case the light is concen- trated upon and is reflected by the object. So that you can clearly understand the action of the rays of light after they are reflected from the object and refracted by the lenses of the microscope take a look at B in Figure 14, which shows diagrammatically how the magnified im- age is formed by a modern compound micro- scope. You will note that the lenses shown are achromatic, but these are shown only to lend the aspect of realism to the diagram, their action being the same as that of the ordinary double convex lens previously shown and described. How the Microscope Forms an Image.—In the first place rays from the mirror through the object A-B and pass up and through the object- ive. By tracing the path of these rays of light, which are refracted on passing through the objective, you will find that a real inverted image C-D is formed near the ocular, or eye- piece ; that is to say, if you placed a screen at this point the inverted image would be thrown upon it. This image is considerably magnified but not nearly enough for the purposes of high power microscopic work. You will observe that this image is inside the principal focus of the ocular lens, so that, as I explained in Chapter II, a greatly magnified upright and virtual image will be formed by the 42 BOOK OF THE MICROSCOPE action of the rays from the image of the object- ive in passing through the ocular as at E-F. You can easily prove this by tracing the diverg- ent rays which emerge from the ocular back- ward in the same manner as you did at C in Fig- ure 8. At the same time, when you look into the eye- piece, the divergent rays emerging from the ocular pass through the lens of the eye, and since these rays emanate from a source that is outside the principal focus of the latter, the divergent rays are once more refracted and brought to a focus when another real inverted image is formed on the retina of the eye. The image which the brain senses, however, is the virtual image E-F, since the rays of light which form the image on the retina of the eye have as their apparent source the image E-F. It is in this way that you see an image en- larged a hundred, a thousand, or even a million times, and, while it does not usually make any particular difference, you should bear in mind when looking through a microscope that the image you see is inverted, or upside down and also reversed, or wrong end to. This fact need cause you no concern, though, for knowing it you will soon accustom yourself to visualizing them as if they were really right side up, and right side to. HOW THE COMPOUND WORKS 43 What Changing the Adjustment Does.—It must, of course, be clear that an endless variety of magnifications can be had with the same lenses in the microscope by simply changing the relative position of one to the other and the relative position to the object itself. For in- stance, if the eyepiece is drawn away from the objective, while the objective is moved toward the object, the image will be formed at a greater distance from the objective than before, and as a consequence it will be even more greatly enlarged. If, on the other hand, the operation is re- versed, that is, the eyepiece is brought closer to the objective, and this is farther removed from the object, then the image will be formed much nearer the objective than before, when it will, naturally, be considerably diminished in size. From this it is evident, in view of extreme magnification of the image formed by the ob- jective by the lenses of the eyepiece, that the adjustment of the lenses in their relation one to the other and to the object must be exceedingly small in order to obtain a sharp image. This being true, the microscope must be built with a good deal of accuracy, and a means for adjusting it must be provided which will permit the lenses to be moved the smallest fraction of an inch at a time. In the following chapter I shall explain the construction of the mechan- 44 BOOK OF THE MICROSCOPE ism employed in both the cheaper and the more expensive types of microscopes. It is neces- sary, however, before going into the details of construction, to explain two other factors which affect the action of the microscope; these are (1) the aberration caused by different media3 and (2) the shifting effect caused by the cover glass. Aberration Caused by Different Media.— First you must know that not only glass re- fracts light, but also air, water, oil and all other transparent substances, or media as they are called, that is, substances through which light readily passes. In mounting microscopic ob- jects a thin glass, called a cover glass, is often used to preserve the mount, as the object is called, and at the same time to protect the objective. The cover glass is placed over the object so that the path of the light waves from the object lies through it as well as through the air between it and the objective of the microscope. This refracts the rays of light in two different ways, and this in turn reduces the number of light waves passing from the object which can be received by the objective. Shifting Effect Produced by the Cover Glass.—Now, if you will take a look at Figure 15 you will see at a glance just how this appar- 8 Plural of medium. HOW THE COMPOUND WORKS 45 ent shifting of the object, or aberration, is brought about. Not only prisms and lenses cause the refraction of rays of light which pass through them, but a piece of plain glass has the same property, though, naturally, to a very much less extent. Hence, as shown in Figure 15, any two rays of light coming from a point on the object which is being examined such as O-A and O-B upon passing through the cover glass are refracted. Objective Refracted Ray of Light | Cover Glass A\ False Position of Object as it Appears when Looking Thru Objective Object* Fig. 15.—Shifting Effect Caused by a Cover Glass When they leave the cover glass, the air between the glass and the objective tends to re- fract these rays still more. The result of this refraction by the cover glass and the air, as far as the objective is concerned, is such that the rays might just as well have had their source at X instead of 0, and when you are looking through the microscope this is to all intents and purposes the case. In like manner the rays from any other point of the object will be apparently 46 BOOK OF THE MICROSCOPE shifted and so change the whole position of the object when viewed through the microscope. This aberration of the cover glass is taken into account by the makers of the objective of the microscope so that the proper correction is obtained. About the Immersion Objective.—High grade microscopes are usually fitted with what is termed an immersion objective, and, as you may have occasion to use one some time, I will tell you about it. You have seen that air also re- fracts the rays of light which pass into it after leaving the cover glass, and this optical prop- erty of the air likewise has an important effect on the action of the microscope. In the first place it is necessary, where a high magnification is needed, that the objective be as small and of as great curvature as possible; and with such a lens, after all the various re- fractions to which the rays of light from the objects are subjected before reaching it, it is very hard to get enough light through to see it clearly. Moreover, it often happens that the rays coming from the point of the object toward the outside edges of a lens are highly important when you are examining the finer structures of it. Should these rays be so refracted that they do not strike the outer edges of the lens, the image formed will not show the minute de- tails of the object. HOW THE COMPOUND WORKS 47 In ordinary microscopic work the air is the medium used between the cover glass and the objective as pictured at A in figure 16, and which clearly shows how the ray O-B is re- fracted by the air after leaving the cover glass. So divergent are these rays that they do not reach the objective at all. To the end that this defect may be corrected, it is evident that some medium other than air, and one having the same “Objective Immersion ,Objectiv® „OptiC Axis Optic Axis A' Air Anqle of Aperture Cover Glass Cover Glass A B Fig. 16.—The Principle of the Immersion Objective refractive power as the cover glass, must be used. At first water was tried as a substitute for air, and, while it gave better results, it did not prove altogether satisfactory. After a great deal of experimenting it was found that cedar oil, which has the same index of refraction (as the refractive power is called) as glass, gave satisfactory results. A drop of cedar oil placed between the object- ive and the cover glass will make the rays, 48 BOOK OF THE MICKOSCOPE which would otherwise be lost in air, pass up to and through the objective as shown at B in Figure 16. An objective so constructed that oil can be used in this way is called an immersion lens; this is one of the greatest single steps ever taken in the improvement of the compound microscope. What the Numerical Aperture Is.—In micro- scopy you will often come across the term numerical aperture in connection with object- ives, and you should know what it means. The angle formed with the optical axis at which the most divergent rays of light pass from an ob- ject through the objective is known as the ang- ular aperture of a lens. It is shown at B in Figure 16. This angle, very naturally, increases as the curvature of the lens increases. Likewise it will be greater when an immersion substance, such as cedar oil is used. From this you will see that the numerical aperture of a lens has a direct relation to the angle of aperture and the refractive power of the oil, or other medium, in front of the lens. It is obvious, too, that the greater the numerical aperture the more effect- ive will your objective be—and consequently your microscope—in viewing an object. CHAPTEE IV HOW THE COMPOUND MICKOSCOPE IS MADE Any kind of a compound microscope, be it a cheap, or an expensive, one, is an instrument of precision. Outwardly, and to all intents, a compound microscope seems rugged enough, but, actually, and of necessity, it is a delicate instrument, consequently (1) considerable thought must be given to selecting one that will properly serve the purpose for which you want to use it; and (2) much care and attention must be exercised in using it. Buying a Microscope.—Like other instru- ments, machines and tools you will find differ- ent kinds of microscopes on the market, rang- ing from a little one that has a magnifying power of 100 times and which costs $7 or $8, to a higher grade instrument that has a magni- fying power of 1,000,000 times or more and which costs several hundred dollars. A cheap microscope will serve your needs as a beginner and for all ordinary household purposes, but if you expect to go very deep into microscopic 49 50 BOOK OF THE MICROSCOPE work, I would advise you to spend $25 or $30 for an instrument. In any event the price you pay for a micro- scope will, no doubt, be determined very largely by your pocketbook. Cheap microscopes can be bought of dealers in optical goods generally. If there is none in your town you can get them from any of the well-known dealers in optical goods in New York, Boston, Buffalo, or Roches- ter. Your first microscope, like your first motor car, will be subjected to various kinds of abuse and so, for this reason if for no other, you should begin with a medium-priced one. Be- fore advising you further as to what to look for when buying a microscope I will tell you some- thing about the construction of the instrument in general, then you will be better able to go about the selection of one intelligently. Parts of a Compound Microscope.—It is a good scheme first to learn the names of the different parts of the microscope and their uses. A recent type of microscope with its parts named is shown in Figure 17, and for conven- ience let us start at the bottom and work up, taking the construction and purpose of each part in turn. As you will see from the picture a good micro- scope has quite a number of parts, the chief ones being (1) the base, (2) the pillar, (3) the COMPOUND MICROSCOPE 51 joint, (4) the mirror, (5) the substage, (6) the stage, (7) the arm, (8) the coarse adjustment, (9) the fine adjustment, (10) the objective, (11) the body tube, (12) the drawtube, and (13) the ocular or eyepiece. 0,1° \v o> ''S’s \ % Ocular .DrawTube Tine Adjust- ment Button. Body Tube Revolving "Nose piece Arm Top Condenser Lens Spring Clips .Stage Quick Adjust- ment: Screw _5ub Stage Condenser Iris Diapnram Adjustment Inclination Joint Mirror "Bar - Mirror Pillar Horseshoe Base Mirror Fork Fig. 17.—Names op the Parts op a Good Microscope The Base.—The most common form of base used in American makes of microscope is the horseshoe type, which, as its name indicates, is made somewhat in the shape of a horseshoe. The base, whatever its shape may be, should give the microscope absolute steadiness in what- ever position it is being used. Unless the base has this property, which de- 52 BOOK OF THE MICROSCOPE pends on (a) the weight of it, and (b) the way in which the other parts are attached, that is, whether it is well balanced or not, however well made it is in other respects, it will never give you the satisfaction that you have the right to expect from it. The Pillar and Joint.—This is an upright solid standard fixed firmly to the base and pro- jecting vertically from it. Its upper end is provided with an inclination joint, into which the lower part of the arm is fitted, the pillar being slotted to receive the keyed end of the arm. By means of this joint, the arm, and, con- sequently, the body of the instrument can be tilted or inclined to any angle between the ver- tical and the horizontal. The joint is made just loose enough so that the arm can easily be tilted to any angle you wish, but will remain in the position you give it unless you again bring pressure to bear on it. This result is secured by means of a pin wThich runs through the pillar and the key of the arm. The pin is usually slightly conical in shape and is threaded on both ends with nuts screwed on them. The necessary friction to make this joint work properly is produced by drawing the conical pin into the bearing; to do this you tighten one of the nuts, which should have either a slot cut in its face so that a screw driver can be used COMPOUND MICROSCOPE 53 on it, or two small holes so that a spanner can be used on it. The Mirror Bar.—To the front of the key is fitted a mirror bar which can be moved side- wise. Projecting from the lower end of this arm and at right angles to it is pivoted a mir- ror fork; this carries a swinging mirror be- tween its prongs. This arrangement of pivots permits the mirror to he turned in all directions and, as with the inclination joint, these pivots are just loose enough to allow the mirror to he swung easily in any direction and at the same time to hold it in place when once it is adjusted. Usually the mirror has two faces, one plane and the other concave; this makes it possible to fo- cus the light on the object under all conditions. The Substage Condenser.—This is a device that is fixed to the under side of the stage, in the better grades of microscopes. The con- denser is made up of achromatic lenses, usually two, mounted in a shallow tube. The purpose of the condenser is to throw a sharp and per- fectly achromatic light on to the object, which in this case must be transparent. To get the best results when using a con- denser the latter must be made almost as care- fully as the objective itself. A cross section through an Abbe achromatic condenser1 is i A further improvement in the condenser is a quick-acting adjusting screw; when this is turned up as far as possible 54 BOOK OF THE MICROSCOPE shown at A in Figure 18; from this you can see how the lenses are arranged. While the cheaper microscopes are not provided with a condenser an important feature of all good microscopes is the iris diaphragm which is pictured at B in Figure 18. Diaphraqm - Iris Diaphram Centerincj Screw Diaphram Lever Fig. 18A.—Achromatic Substage Fig. 18B.—The Iris Condenser with Half Cutaway Diaphragm to Show Lens Combinations Where the microscope is fitted with a con- denser the diaphragm is placed between the achromatic lenses as shown at A. The iris dia- phragm is so named because, like the iris of the eye, or pupil, it is a mechanism by means of which the amount of light passing through it can be regulated. In the human eye this func- tion is performed automatically, while in the microscope it is done by changing the position of a small lever that projects from the side of it. The diaphragm itself consists of an ingenious the upper lens of the condenser is brought into the stage so that it can be used in immersion contact with the slide in the same way and for the same reason that I have described for immersion objectives. COMPOUND MICROSCOPE 55 arrangement of small overlapping plates or leaves, and as the lever is moved one way or the other they close and give a large central aperture, or spread out and give a small aper- ture for the light to pass through. It is made on exactly the same principle as the shutter of a camera. The Stage.—This is a small platform that is rigidly fixed to the lower part of the arm and upon which the object is placed when it is to be examined through the microscope. It is formed of a slab of metal or hard fabricated material with a small hole in its center so that the light reflected by the mirror can be projected up and through the object on the slide. The stage is fitted with a pair of spring clips to hold the slide that contains the microscopic object in position. A convenient form of stage, but which comes only on the higher grade in- struments, is the revolving type. It is so made that the stage and object fixed to it may be rotated so that it can be viewed from all angles. A revolving stage, however, is not a necessary adjunct to good work. Still more expensive in- struments are provided with a mechanical stage in which the slide can be moved by turning a thumb screw; in this way any part of the ob- ject can be brought quickly and accurately into the field of the objective. The Arm.—The makers of microscopes are 56 BOOK OF THE MICROSCOPE constantly improving them even as to design. The slotted arm pictured in Figure 17 is to my way of thinking easier to handle than the later type with the long curved arm shown in figure 18, but this may be because I am more accus- tomed to the use of the former. The curved arm, however, has an advantage in that it is easier to manipulate the slide on the stage be- cause the latter is left more open. Either design will fully satisfy your needs. The Coarse Adjustment. —This adjustment, the purpose of which is to enable you to focus rapidly the object on the stand, is secured to the upper part of the arm. The mechan- ism that is in general use is known as the rack and pinion adjustment. It consists of a rack, that is, a strip of metal with teeth cut in it, fixed to the body tube of the microscope, and a pinion, which is a small- toothed wheel, mounted, on the arm. The teeth of the pinion mesh with the teeth of the rack, and when the coarse adjustment screws are turned the pinion causes the rack to move up or down according to the direction the screws are turned as shown at A in Figure 19. The rack is protected by sliding in a groove Rack Pinion Adjusting Button Fig. 19A.—The Coarse Adjustment COMPOUND MICROSCOPE 57 in the arm which prevents dust and dirt from getting into the teeth. If you should ever buy a used microscope see that the rack and pinion work smoothly; you should also observe wdiether the rack is greased, as this is some- times done to cover up the defect of well-worn teeth. It is easy to tell by the feel of the milled Eye Piece Rack -Pinion Box .Coarse Adjust- ment Buttons Pivoted Lever • "Screw Fine Ad just- Tnent Side Buttons Flange- A A Fig. 19B.—How the Best Type of Fine Adjustment Is Constructed adjusting screws if the rack and pinion move- ment is in good working condition. The Fine Adjustment.—Of even greater im- portance than the coarse adjustment is the fine adjustment, for it is with this latter mechanism that you get the final focus. Without regard to the merits of the other parts of the instrument the fine adjustment must work smoothly and accurately, hence the mechanism which pro- duces this result must be delicate and of limited range. 58 BOOK OF THE MICROSCOPE There are two distinct kinds of fine adjust- ments in use; in the first one micrometer head is secured to the top of the arm, and in the second two micrometer heads are secured to the opposite sides of the arm. This latter ar- rangement is the one that is most commonly used; its construction is shown at B in Figure 19. It is very durable, since it is built with the fewest number of parts possible and has only two bearing surfaces. The side buttons A are fixed to the screw B which carries a heavy flange C. The screw has two bearings; the one on the right hand has a fine thread which engages with the micrometer threads of the screw, and the one on the left hand is plain, since the screw is not threaded at this end. When either of the side buttons are turned the screw travels into or out of its bearing, and the heavy flange C works against the pivoted lever D so that when the flange is carried forward the lever is raised, thus car- rying the body tube with it, or lowering it if the movement is reversed. One revolution of the focusing button moves the tube twTo milli- meters up or down. The Objectives.—A microscope of fair power should have at least two dry objectives—that is, objectives that work with air between them and the object. One of these should be of low power and the other of high power. An oil im- COMPOUND MICROSCOPE 59 mersion objective is also handy to have as part of the equipment, although this is not neces- sary for elementary work. Objectives of the first kind are fixed, that is, the lenses are secured in the tube so that they cannot be changed. Adjustable objectives, in which the position of the lenses can be changed in order to compensate for the shifting of the object and variations in the cover glass, are also made, but they are useful to skilled micro- scopist only, as he only would thoroughly un- derstand them. Those of the fixed type will serve your every need. Where two or three objectives are used, as in the better grade of microscopes, they are secured to a revolving element called a nose piece. The rotating part of the nose piece car- ries the objectives and the fixed part of it is attached to the lower part of the body tube. This arrangement is so made that one can change from one objective to another by simply turning the nose piece around, when the objec- tive you want to use will be under the body tube and in a line with the eyepiece. These nose pieces are made so that they loch when the objective is in the right position for use. They are also made parfocal, that is, they are so designed and constructed that if one of the objectives has been focused on an object and another one of higher or lower power is swung 60 BOOK OF THE MICROSCOPE into its place, it will also be in fairly good focus. Moreover, tbe objectives are pretty closely centered, so that a point in tbe center of tbe field of one of tbem will be in tbe center of tbe field of the other, when it is swung into place. Of course tbe objectives are aplanatic and ach- romatic as described in Chapter III, and they are corrected for a tube of standard length, which is 160 millimeters, and for aberration caused by a cover glass that has a thickness of .18 millimeter, which is the usual thickness. The Body Tube.—This is the main tube, and while it acts as a support for the lenses, it car- ries no lenses itself. The purpose of it is to hold the drawtube and to provide a convenient means of protection for the former as well as a rigid mounting in which it can be moved up and down. The body tube further carries the rack fixed to it for the coarse adjustment. The Drawtube.—In the upper end, and mov- ing in a cloth-lined sleeve, is carried the draw- tube; this in turn holds the ocular or eyepiece. In the better makes of microscopes the draw- tube is often graduated to show what the tube length is, that is the distance from the objective to the ocular as it is drawn out or pushed into the body tube. The purpose of the drawtube is to vary the distance between the ocular or COMPOUND MICROSCOPE 61 the eyepiece, the objective thus increasing or decreasing the magnification of the object. The Ocular or Eyepiece.—This is carried by the upper end of the drawtube and consists of a doublet, that is, two lenses mounted in a short tube. Oculars are made that give different magnifications and are, therefore, either let- tered or numbered to show what the magnifica- tion is. A good microscope usually has two oculars, one of which gives a magnification of, say, 5 times, hence the ocular is marked 5X; the other gives a magnification of 10 times, or 10X. All up-to-date oculars made by American manu- facturers are marked in this way, and this mark represents the increase in magnification that the ocular gives to the real inverted image which is formed by the objective. Thus if the objective has a magnifying power of 10X, that is, if the image formed by it is 10 times larger than the object itself, when an ocular marked 10X is used, it will produce a virtual image which is ten times as large as the image produced by the objective, or 100 times larger than the object itself. You can also determine roughly whether an objective, or an ocular, is of high or low power by its length. A long ocular is usually of low power, while a long objective is, as a rule, of high power; and the other way about is also 62 BOOK OF THE MICROSCOPE true for oculars and objectives which are short. The relative sizes of the lenses in oculars or objectives also determine, in a measure, their magnification, for large lenses in the first usually show high power, and, in the second, low power. CHAPTER V THE RIGHT WAY TO USE A MICROSCOPE From what I have told yon in the foregoing chapter you will see that the microscope is an instrument that needs care and must be handled with consideration, so now a few simple direc- tions as to how to use it are in order. Getting Your Microscope Ready for Work.— If you have just bought a microscope you will find it packed in a neatly made box or case, and this you should keep. When you are not using the instrument, you should always keep it in the box, as this will prevent dust and dirt from getting on and in it. If you have a high grade instrument, you should procure a bell jar to set over it when it is not in use, as this makes it easy to get at and at the same time it requires less handling. On opening the box or case, you will find the microscope all assembled and ready for use, with its objectives in place and the ocular in the drawtube. In taking the instrument from the box the safest way is to pick it up by the base with one hand and by the arm with the other 63 64 BOOK OF THE MICROSCOPE hand. In removing it be very careful not to strike the adjustments or the nose piece, if there are any. When you have it out of the box you can hold it by the arm, but if you intend to carry it any distance always use the box. How to Take Out the Objective.—The next step is to take out the objective and ocular and clean them. To remove the objective from a cheap microscope, you need only to unscrew it .Nosepiece Objective Seat from the tube, but to remove the objective from the nose piece of a high grade instrument, you must go about it a little differently. The first thing to do when you want to take out an objective is to raise the tube of the microscope by means of the coarse adjustment until the lower end of the objective is well away from the stage; then you can easily grip it with your fingers. The nose piece should be turned around until the objective which you want to Fig. 20.—How to Remove an Objective RIGHT WAY TO USE 65 take out sets at its outer edge and to the front of the microscope. Now grasp the objective lightly at its lower end with the forefinger and thumb of your left hand, and take hold of the milled ring near the lower end of the objective with your right hand as shown in Figure 20. You can then unscrew it without danger of dropping it. How to Put the Objective Back.—When put- ting the objective back in the nose piece use both hands as before. In doing this, however, even greater care must he used than when tak- ing it off, and you must see that the threads of the objective mounting are started evenly with the threads of the nose piece. Should you fail to get the threads to mesh evenly, you will not only break them but the objective will be thrown out of line. It is not at all difficult to screw the objective in right, but as the threads are very fine and the position a little hard to work in, they will not always start in even. If the threads should become damaged by careless insertion of the objective you will have to get both the mounting of the objective and the nose piece rethreaded by some optical instrument maker and this will take time though it may not cost you very much. How to Take Out the Ocular.—When you want to take out an ocular grip it by the milled ring next to the eyelens and hold the micro- 66 BOOK OF THE MICROSCOPE scope either by the coarse adjustment or by the tube. Now, if you give the ocular a gentle but firm rotary and upward motion it will leave the instrument easily. As with all lenses be careful not to drop it. How to Put the Ocular Back.—To put back the ocular you simply reverse the operation des- cribed above for taking it out; you should see however, that the objective is raised a goodly distance from the stage, especially if a slide is in place. If this is not done and your ocular fits rather snugly into the drawtube, you are liable, in pressing it down, to push the objective down also, in which case it will come into con- tact with the slide with undue force. How to Clean the Optical Parts.—After you have taken the oculars and objectives out, lay them on a soft cloth to prevent them from be- coming scratched. It is evident that, unless the lenses are absolutely clean, no matter how care- fully you adjust the instrument you will not be able to get anything like good results. Should you find that the lenses are dirty, wipe them gently with a piece of Japanese lens paper, which you can get from any optical sup- ply house. You can use a piece of very soft linen instead of the paper, but it must be per- fectly clean. Never use chamois skin, for you cannot really clean a lens with it because it contains natural oils that are apt to (1) form a RIGHT WAY TO USE 67 film on the surface of the lens, and (2) cause dust and dirt to stick to the film, which, on cleaning the lens again, will scratch it. Always rub a lens very gently when cleaning it, for, should there he any grit on it, there is always danger of scratching it. Further, you should never touch the surface of a lens with your bare fingers as they contain natural oils. Moreover, there is apt to he some slight perspiration on them, and when this gets on the lens it is very hard to get off. When picking up a lens that you have taken out of its mounting, you should either pick it up by its edges as shown in figure 21, or with a piece of fine linen cloth. How to Clean an Objective.—Sometimes the front lens of an objective, that is, the lens that is exposed, becomes so soiled that you cannot get it clear merely by wiping it. In this case try breathing on it and then wiping it. Should this fail to remove the film of dirt moisten your Japanese paper with a few drops of xylol or chloroform; this will take it off. Be sure to wipe the lense perfectly dry after you use these cleaning agents. Then, too, it will be found that dust often settles on the back lens of an objective even Fig. 21.—The Prop- er Way to Handle a Lens 68 BOOK OF THE MICROSCOPE though the eyepiece has been left in the tube, as it always should be. If dust has settled on the back lens never try to take the objective apart, for this is a job that belongs to the in- strument maker. Use a small camel’s hair brush to remove this dust; usually this is all the back lens ever needs. After using an immersion objective yon should clean it immediately; this you can do by gently wiping it dry with a piece of lens paper. If the cedar oil has been allowed to dry on the lens you can get it off either with xylol or chloroform. The better way is to clean your immersion objective as soon as you have used it. How to Clean the Ocular.—The same methods of cleaning the oculars are used as those des- cribed for the cleaning objectives. A grayish film is sometimes formed on the inner surfaces of the lenses that make up the ocular. When this happens, remove the lenses from the tube as follows: both the upper and lower ends of the tube have a milled ring which holds the lenses, and these screw into the tube. By un- screwing these from the eyepiece you can get at the inside surfaces to clean them. After taking out the lenses, you will find, about one third of the distance from the lower end of the ocular tube, a metal ring, known as the ocular diaphragm; you should clean this also. RIGHT WAY TO USE 69 How to Clean the Condenser and Mirror.—If your microscope has a condenser yon should clean it with the same care and in the same way that I have described for the objective and the eyepiece, since the best results can be obtained only when the condenser is perfectly clean. The mirror also should be well cleaned. When you have all of the parts thoroughly cleaned you are ready to give your microscope a tryout but not before. Choosing a Place to Work.—The choice of a place to do your microscopic work is of great importance. The first essential is good light, the next plenty of room and at the same time comfort. Microscopic work is absorbing and once you have started in to examine objects you will not want anything to interfere. Therefore, be sure that everything is as it should be before you start. Having found such a place set your micro- scope on the table near the edge, as shown in Figure 22; the table must be neither too high nor the chair too low for you to look into the instrument without straining yourself to do it. If you are working with fresh mounts or fluids you will have to keep the stage parallel with the table top, that is, in a horizontal position. If, however, you are working with the object mounted on a glass slide you can tilt the micro- scope by means of the inclination joint to any 70 BOOK OF THE MICROSCOPE position where you can see to the best advant- age. It is considered the best practice, though, always to use the instrument in a vertical posi- tion as shown in Figure 22. A* A Cheap Microscope Magnifies IIOTimes Fig. 22.—The Correct Wat to Use a Microscope Getting the Right Light on Your Work.— Using Daylight.—As I have already pointed out, next to the instrument itself the chief thing in using the microscope is to get the best light on the object under examination that you can If you pay attention to this all-important fact- or, and also learn to use your microscope with both eyes open and to use either eye at will, no BIGHT WAY TO USE 71 reasonable amount of work will injure your eyesight. But you should never work in the direct sun- light, for too bright a light is as bad for the eyes as too little; instead, choose a place that is well lighted from the reflection of the sky alone. Further, there should be no object di- rectly between you and the source of light, such as the moving branches of trees or shrubbery, or the wire netting on the window, as these all prove annoying. So much for the use of natural light, which is far better than artificial light for your eyes if you can get it. Using Artificial Light.—Should you have to use artificial light, it is absolutely necessary that it be steady, that is, the light must be equal in intensity and quality, and must not flicker. A good light of this kind is that given by a tungsten filament electric lamp which has a ground glass bulb. Where an electric light is not available a Welsbach gas mantle light, or even an ordinary gaslight, can be used; if the latter is used, the narrow edge of the flame in- stead of the broad side should be set toward the mirror. You will remember that a light which is small and near gives off divergent rays, and, there- fore, when using an artificial light, place a con- densing lens between it and the mirror of the 72 BOOK OF THE MICROSCOPE microscope, so that the divergent rays will be brought to a focus. Further, to soften the light, you should place a piece of blue glass between the light and the mirror, or better, use a glass globe filled with a solution of ammonium copper sulphate; this will act also as a condenser. The globe should be mounted in a frame or shade so that all the other rays from the light, except those that go through it, will be cut off from the microscope. Finally, you will find it to your advantage, when using an artificial light, to wear an eye shade that will shut out all outside rays, as it is these that are the chief cause of eyestrain. How to Focus Your Microscope.—Put a low power objective and ocular in place, and then insert a slide with a transparent object on it that you want to examine under the spring clips on the stage. Now adjust the mirror so that when you look through the ocular the field of the objective appears to be illuminated evenly and brightly. You should then bring the ob- jective down until it nearly touches the object, or cover glass, if the object is permanently mounted, and in doing this you should use the coarse adjustment. This is known as focusing down; while doing this you should watch the movement of the objective from the side to see that you do not run into the object. Next place your eye close to the eyepiece, and EIGHT WAY TO USE 73 with the coarse adjustment bring the objective away from the object, or focus up, as it is called. You will soon reach a point where you will plainly see the object. This done you are ready to use the fine adjustment which will give you the sharpest focus possible and, hence, the best definition. You can safely focus up with the fine adjust- ment, but you should be very careful in focusing down, because the movement of the objective is so very small for the distance you turn the adjusting button that you are very apt to run the objective on to the object. As you are focus- ing with the coarse adjustment, it is a good plan to keep the object moving about a little on the stage, as it is easier to find it, that is, to get it in the center of the field, when it is moving than when it is still. At first you may become confused by the fact that the image as seen by your eye is reversed, and also by the act that the microscope magni- fies the movement as well, thus making it appear as if you were moving it faster than you really are and in the opposite direction. You will need only a very little practice to be able to adjust the object to a nicety. The right way to examine an object is to use a low power objective and ocular first before trying a high power, because a low power shows more of the object and thus gives you a better 74 BOOK OF THE MICROSCOPE idea of its general appearance. When yon want to examine some particularly interesting part of an object you can switch over to a high power objective and ocular, as this will bring out all the finer details. In the next chapter I shall tell you more about focusing, but the above hints are all you need for your first experi- ments with the microscope. How to Care for the Other Parts.—In the beginning of this chapter I told you how to keep the optical parts of your instrument in good condition, and, in closing, I will tell you how to take care of the other, or metal parts. The parts of a microscope that are enameled or lac- quered can, as a rule, be readily cleaned by rub- bing them down with a soft cloth or a piece of clean chamois skin. Fingerprints, however, are sometimes hard to remove by this means alone, and when this is the case you can try breathing on the surface first before rubbing. Should this fail, use a cloth slightly dampened with water, and, as a last resort, use alcohol, ether, xylol or chloro- form. Do not use any of the latter unless the enamel or lacquer is in very bad shape, as they are liable to remove it along with the finger- prints. In any event dry the instrument im- mediately after cleaning. How to Care for the Stage.—After a while the stage, especially if it is on a cheap micro- RIGHT WAY TO USE 75 scope, will turn gray. This is apt to be partic- ularly so after it has become soiled with bal- sam, immersion oil and other substances which you cannot get off with wrater. To restore the original black luster of the enamel all you need to do is to rub it with machine oil and then wipe off all the excess oil after the finish has taken on its original polish. Taking Care of the Coarse Adjustment.—If dirt or other foreign matter should get into the teeth of the rack and pinion, the adjustment will not work smoothly. If this should happen don’t force it up and down but clean the teeth with xylol or chloroform, then lubricate with a very little watch oil, or any light machine oil that is free from acids. Once in a while the bearings may work loose and then the tube will rattle or sway every time you turn the coarse adjustment button. To remedy this, tighten the small screws which are located at the back of the pinion box; this will take up the lost motion. Never try to fill up the teeth of the rack with anything in order to take up the lost motion. Taking Care of the Fine Adjustment.—If you wish to keep the fine adjustment in working order the one thing you should never do is to take it apart. In some micrometers, especially the older kind, no provision is made for stop- ping the movement at both ends of the range of 76 BOOK OF THE MICROSCOPE the screw; if your instrument is of this kind, and yon are not careful you are as likely as not to run the threads out of their bearing. Should the screw become thus removed from its bearing it must be replaced with a deal of pains, for the threads are so tine that it is just as easy to start the screw back into its bearing so that the threads will run as it is to start it properly. If you should be unfortunate enough to make the threads run, the only thing to do is to send the instrument back to the maker and have him rethread the screw and its bearing. Nearly all of the later model microscopes, however, are so constructed that the micro- meter screw has a stop at either end of its range which prevents it from being run out of its bearing. Whatever you do, never force the micrometer head when it fails for any reason to work smoothly. How to Clean the Substage.—Should the leaves of the iris diaphragm get gummed up, rusted or dirty, they can be cleaned with xylol, after which you should dry them thoroughly and put the minutest amount of watch oil on them, at the same time working the diaphragm lever back and forth to distribute the oil evenly. Sometimes the threads on the quick-acting screw of the condenser adjustment get gummed up; this can also be remedied by taking out the screw and cleaning it with xylol. EIGHT WAY TO USE 77 Taking Care of the Nose Piece.—The nose piece can be cleaned in the same way as the other metal parts of the instrument. There are, however, four donVs which you must heed: (1) don’t put oil between the rotating and station- ary parts of the nose piece; (2) don’t strike or do anything else to bend the position of the nose piece; (3) don’t interchange the objectives (that is, do not put the low power objective where the high power objective was in the nose piece, or the other way about); (4) don’t focus down on the object until you have focused up and changed over from a low to a high power objective unless you are sure that your objec- tives are parfocal. If your objectives are not parfocal and you do not follow these instructions, the high power objective which is longer than the low power objective will strike the object and both may be damaged. By following the advice that I have given you in this chapter, your microscope will serve you well to the end of your days at little or no expense and with pleasure and satis- faction to yourself. CHAPTER VI THE LIGHTING OF MICROSCOPIC OBJECTS I have already pointed out the importance of proper illumination when you are doing mi- croscopic work, and although I have told you in general how to get the right light on the ob- ject, there are some particular points which you should know about. Kinds of Microscopic Objects.—In the first place there are two classes of objects which you will want to examine with your microscope, namely, (1) transparent objects, and (2) opa- que objects. Transparent objects are those through which light can readily pass, and, hence, can be illuminated from a beam of light under them; opaque objects are those through which light 'will not pass and, consequently, must be illuminated from above. Objects for the microscope are of both kinds; those that are transparent, or semitransparent are usually formed of thin sections, that is, slices of vegetable or animal matter, while those that are opaque include masses of matter, 78 LIGHTING OF OBJECTS 79 such as whole insects, most minerals and all the metals. The kind and extent of the lighting required to get the best results depend upon the nature of the object you want to examine. How Transparent Objects Are Illuminated.— For the proper illumination of transparent ob- jects there are two means by which the light can be carried from the object to the objective, namely, (1) the axial, or central, light, and (2) the oblique light. The Axial, or Central, Light.—By the term axial, or central, light is meant rays of light which strike the ob- ject and illuminate it in such a way that the rays are all arranged evenly, or symmetrically, as it is called, around the optical axis of the objective as shown in Figure 23. In other words, the objective is evenly illuminated. I have already explained how different sour- ces of light produce parallel or divergent rays according to their size and distance from the object. Thus, when natural light, that is, ordi- nary daylight, is used, the mirror must be ad- justed so that the parallel rays will be reflected upward and through the object evenly from all Vacuole Ectosarc Jcndosarc. Pseudopodi* Nucleus Protoplasm Fig. 39.—The Amoeba—A Unicelled Animal in the algae, is the life center of the cell, and the contractile vacuole is the means by which waste gases and fluids are removed. The food vacuoles engulf the minute food particles which are then digested providing the body with nour- ishment. The lobate projections are formed by an extension of the ectosarc and endosarc and the amoeba moves about from place to place by means of these fingerlike extensions into which the substance of the body is transferred. Like the algae, the amoeba multiplies by the process of simple division of its cells. Under LOWEST ANIMAL SPECIMENS 141 the microscope you will sometimes observe that one of the lobate projections becomes enlarged and fixed at the extremity, and the neck con- necting it to the body will contract or thin away, until the lobe separates entirely from the latter. The detached part then becomes an independent amoeba. The Sporozoa.—These are protozoan ani- mals which are characterized by the manner in which they reproduce. They are parasitic ani- mals found in the intestinal canal of insects, worms and the higher animals and they repro- duce their kind as follows: the body of the ani- mal takes on a globular form and becomes en- cysted, that is, covered by an envelope, or cyst. The nucleus next disappears, and the sub- stance, or protoplasm, in the cyst breaks up into particles which are called spores, spher- ical or oval forms. The cyst then bursts and the spores escape, and, after passing through an amoeboid1 stage, finally develop into adult Sporozoa. Mastigophora and Infusoria.—These proto- zoans have more or less fixed cell walls, and possess a few or many cilia, which are used in locomotion. They may travel at great speed when seen under the microscope, and unless you use some glycerin jelly or other harmless ma- terial which will slow them down, you won’t 1 That is like an amcBba. 142 BOOK OF THE MICROSCOPE make out much about their structure. They may be found in stagnant water where there is considerable decaying plant matter. The ani- mals possess the same structures as were de- scribed for the amoeba. The Metazoa, or Multicelled Animals.—Next higher in the scale of animal life are those which have a multicellular structure, or Meta- zoa, as this great division is called. In animals of this kind the egg cell divides and the cells that result from this process combine so as to form an organic whole, or life unit, and the various groups of cells then perform the dif- ferent functions for the animal; or, to put it another way, the cell groups are developed into organs. The Porifera.—The most simple of the Meta- zoan animals are the Porifera, or sponges, as they are commonly called. Now the sponge you buy in the drug store and the sponge as a liv- ing animal are two very different things, for in the first what you see is only the horny skel- eton which is formed of a substance called Spon- gin—an organic material, and this is often strengthened by mineral deposits; hence it is entirely without life. In life the sponge consists of this skeleton, or framework, upon which are two layers of cells which form a system of canals and cavi- ties. These passages are lined with fine, hair- LOWEST ANIMAL SPECIMENS 143 like processes, or flagella, as they are called, and move constantly back and forth. The move- ment of the flagella sets up currents of water in the canals and cavities, the incoming cur- rents drawing the necessary food and oxygen into the sponge while the outgoing currents carry off the waste matter through the oscula,2 or exhalant pores, as shown in Figure 40. Osculum Pores Framework Flagella Flegellated Chamber Amoeboid Cells Fig. 40.—The Structure of a Sponge—A Sac-like Animal Sponges reproduce themselves in two differ- ent ways: (1) nonsexual, and (2) sexual. In the first way spores are formed within the flag- ellate chambers which are set free through the oscula, and this lays the foundation for a new colony of sponges. In the second way certain cells of the sponge are transformed into sperm cells and these develop spermatozoa—the male cells. Other cells, known as egg cells, and which are the female cells, after being fertilized by the 2 Plural of osculum. 144 BOOK OF THE MICROSCOPE sperm cells, develop into ciliated cells, that is, cells having hairlike processes, and by means of these they are able to swim out of the oscula in the parent sponge and begin life for them- selves. Later these grow into sponges like the parent from which they come. The Coelenterata, or Zoophytes.—We now come to a group of animals that, while a little higher in the scale than the sponge is more or less plantlike, the Coelenterata (pronounced Cel-en"-ter-a'-ta) or Zoophytes. While these are Metazoic animals, that is, multicellular, at the same time they are peculiar in that some of the cells which go to make up the animal keep, to a large extent, their independence. This is shown by the fact that, while the ani- mal has a multicellular organ called a digestive sac, the individual cells which line this sac are really the means by which food is taken into the body. A further evidence of the property of protozoic independence maintained by the cells is the property of the animal to reproduce itself from a minute portion of any part of it. This phylum of animals can be divided into three classes: (1) the Hydrozoa, (2) the Scy- phozoa and (3) the Anthozoa. The Hydrozoa or Polyps.—To this family belongs the fresh water Hydra, a very common kind and one which is found in nearly every fresh-water pool and pond. The body of this LOWEST ANIMAL SPECIMENS 145 little animal is a sac usually consisting of a long, slender cylinder, having at its upper end an opening, or mouth, which is surrounded by numerous arms, or tentacles, as shown in Fig- ure 41, which are covered with wartlike pro- tuberances, called nematocysts. In the center of each of these is a dart, and when the Hydra wraps its tent- acles around the living body of some minute water animal, the dart is pro- jected into its body when it quickly dies because of some poison poured out from the nematocyst. In this way Hydra gathers in its food, the long arms tak- ing it to its mouth which opens directly into the body sac, or the so-called stomach. At the base of its body is a suctorial disk and by means of this the Hydra attaches itself to the leaves and stems of water plants. Like the sponge the Hydra reproduces itself by both sexual and nonsexual means. The Scyphozoa, or Jelly-fishes.—The animals in this class are nearly always free-swimming, and are shaped very much like a bell. In these two ways they differ strikingly from the Hydro- zoat but in other respects the two are similar. 5 Tentacles Stomach- ‘Bud Suctorial - Disk * Fig. 41.—The A Plantlike Animal 146 BOOK OF THE MICROSCOPE The Scyphozoa possess the stinging cells, many tentacles, and a stomachlike sac in which food is digested. Some of them may grow very large as for example, the Japanese man-of-war, a common form in the Gulf stream. They re- produce by means of sperms and eggs, the usual sexual method. The Anthozoa, or Sea Anemones and Corals.— These marine animals grow in colonies, and the soft tissues of the individual members of a col- ony are held together by means of a mineral deposit with the result that a rocklike mass is formed. The latter contains numerous circu- lar cells in which there are vertical partitions, or Lamellae, as they are called, and these make the stomach and the rest of the organs lie in separate chambers. Now the structures of the animals which I have told you about up to this time are more or less simple from a zoological standpoint, but with animals from now on which are higher in the scale of life than the zoophytes, the structures rapidly become more and more com- plex. Since this is the case I can give you only a brief description of the main phyla, but in so doing I shall point out those features of the structures which are the most interesting wThen examined under the microscope. The Echinodermata, or Sea Urchins and Star- fish.—The first of these higher animals are the LOWEST ANIMAL SPECIMENS 147 sea urchins and starfish, or Ecliinodermata (pronounced E-chi'-no-der'-ma-ta) as they are known. Like the Anthozoa described above, these animals have a calcareous skeleton, that is, one composed of calcium carbonate, or lime- stone, as it is commonly called. The skeleton gen- erally consists of a number of layers of calcium carbonate, superimposed one on the other and joined together by short ribs of the same material; the openings of one lay- er are so placed that they come over the solid portions of the layer under it and form a kind of a network. Animals of this order are further provided with teeth which your microscope will show to have a structure very like that of the skeleton and a shape very like that of the front teeth of rodents, that is, animals of the gnawing type, with the exception that these teeth are rein- forced on both sides by short rods of calcium carbonate, and these set into the main part of the tooth as shown in Figure 42. The teeth themselves are set in jaws, or plates, whose structure is identical with that of the skeleton. ,Axi5 Body -Keel Enamel-Ilk^ Substance' Fig. 42.—A Tooth of Echinus 148 BOOK OF THE MICROSCOPE Members of this order show what is called radial symmetry, which means that the various parts of their structure are arranged and ra- diate from a common starting point like the spokes of a wheel from the hub. The very young stages of the EcJiinodermata are larvae3 which have bilateral symmetry, that is, two sides are symmetrical with a ciliated4 fringe arranged around them. The embryo is unlike the parent in many respects, but later resem- bles it, and as growth takes place the substance of the parts of the embryo which are not needed in the parent is used to feed the growing em- bryo. The Vermes, or Worms.—Next in order of complexity of structure is the subkingdom of animals whose scientific name is Vermes, but which are commonly known as worms. There are three phylo of worms: (1) the Platyhel- mintlies, (2) the Nemathelminthes, and (3) the Annelida. The Platyhelminthes, or flat worms.—This is the scientific name that is given to all worms which are flat and not segmented, many of which are parasitic within the bodies of other living animals; one of these parasites is the Tapeworm, classified under the head of Ces- toda. They are often found in the intestinal 3 The maggotlike young of insects. 4 That is, hairlike. LOWEST ANIMAL SPECIMENS 149 passages of both man and beast and grow to great length. These worms live by absorbing the juices produced within these organs. The common tapeworm has no mouth or stomach and each segment of which the body is composed con- tains its own reproductive organs, the male and female, which are combined so that each seg- ment can produce its own eggs independent of the other segments. The segments are usually connected by two pairs of canals running lengthwise which seem to form a sort of vascu- lar system. The Turbellaria.—This is another order of flat worms that is characterized by cilia, or fine hairlike processes, which cover the entire sur- face of the body. These worms are found in both fresh and salt water and therefore are quite common. In general the body is rather long, having a flattened, solelike shape, and is provided with a suctorial5 mouth so that it can attach itself to its prey and draw out its nour- ishment. The mouth opens into a short tube, the eso- phagus, which in turn opens directly into the cavity of the stomach. The stomach is very curious, for from it a large number of canals extend so that they reach every part of the body as shown in Figure 43. In this way the ani- 6 That is, a sucking mouth. 150 BOOK OF THE MICROSCOPE mal lives without a true circulatory system, since the canals serve as a circulatory and gastro-vascular system at one and the same time. These animals sometimes reproduce by sex- ual means, but usually they split down the middle when each segment so formed becomes Stomach Sucker-like - Mouth Gastric -Canals -Male 5exual Organs Female Sexual .1 Organs Fig. 43.—A Longitudinal Section of Worm of the Class Turbellaria an individual animal, and may, in turn, divide in like manner. In the light of their ability to reproduce from a small part of the body, the Turbellaria are very like the Hydra about which I told you before, although their general structure is of a much higher nature. The Nemathelminthes or round worms.— These worms can easily be distinguished from the Platyhelminthes, because they are cylin- drical in shape, tapering at both ends. Some LOWEST ANIMAL SPECIMENS 151 of them live freely in the soil and water every- where, and some are parasitic, living within the bodies of other animals. Yon may be al- most sure of finding some if yon examine most any foul, stagnant water, or look within the intestines of frogs, cats, dogs, horses, etc. One of the worst enemies of the farmer is a round worm, whose name is Ascaris, and which lives in the intestines of all domestic animals and sometimes of man. If the hosts are not prop- erly cared for, this little round worm will kill a whole herd of animals. Another important one is Necator, which causes the terrible hook- worm disease. You will find it very easy to examine members of this phylum by getting some Anguillulidoe (pronounced An"-guil-lu-li'- dea) which are little eel-like worms. Anguillu- lea glutinous is the name given to that partic- ular kind known as paste eels which develops in sour paste. These eels are often found in vinegar, when they are called vinegar eels, or to give them their scientific name Anguillulea acetic. If you will examine these eels under your microscope you will be entertained with a very remarkable spectacle. The Annelida.—Members of this phylum in- clude those worms which are highest in the scale of their kind and which show well-defined segments, and are for the most part elongated, that is, long in shape. In some worms, as the 152 BOOK OF THE MICEOSCOPE leeches, the division into segments is not so well defined. Upon the outside shape of the Annelid worms depends the kind of respiratory append- ages they have. In the Tubiculous forms, which have a hard, shell-like outer skin that incloses the softer tis- sues of their bodies, the respiratory organs, through which the fluids of the body are sent for aeration,6 are located on the head, while in the non-Tuhiculous species wThich can swim about freely or crawl, since they do not have a shell-like skin, the respiratory organs are located on the sides of the animal. In this lat- ter species, which are carnivorous, that is, meat eating, the mouth is horny, or armored, as it is called,and isprovidedwithstrongteethand jaws. Under the microscope you will plainly be able to see the circulation of the fluid in these respiratory appendages. The fluid is of two kinds, the first being a colorless one which con- tains cell-like corpuscles, and is found in the space between the alimentary canal and the inner wall of the worm’s body. You will see that it passes into canals which enter the res- piratory organs but that no return system is provided. Another fluid that is red will be seen; this is carried along by a system of ves- sels in the body, propelled by a dorsal7 vessel. 6 To be exposed to the air for purification. 7 Dorsal means situated near the back. LOWEST ANIMAL SPECIMENS 153 This latter organ acts as a respiratory heart and drives the fluid through the respiratory vessels and then is directed back again. The Annelids are oviparous, which means that they produce eggs. The embryo comes forth from the egg in a very undeveloped con- dition and consists of a mass of cells; some parts are provided with cilia. Shortly after emerging from the egg, this mass becomes elongated and the appearance of segments is shown more or less clearly by rings. Finally the various internal organs begin to shape themselves into segments, and eventually all of the organs and appendages are produced that are found in the adult. CHAPTER XI HIGHER FORMS OF ANIMAL SPECIMENS UNDER THE MICROSCOPE By this time yon have gathered that the fur- ther yon get along your work with the living animals, the more complex the structures of their bodies become, and it follows, to some ex- tent, the larger the animal becomes, although this does not always hold good. The next higher class of animals is commonly known as shellfish which are scientifically called, Mol- lusca. The Mollusca, which include the oyster, clam, cuttlefish, snail and slug, are a step higher in the scale of life, than the worms. There are three kinds of these animals: (i) those that have a two piece, or bivalve shell; (2) those that have a one piece, or univalve- shell; and (3) those that are naked, or have no shell at all. The class called Gastropoda in- cludes those that are univalve. This class has a very curious structure of the tongue, or pal- ate, and the development of its embryo, which will be described presently, is also interest- ing. 154 HIGHER ANIMAL SPECIMENS 155 The Mollusca.—The structure of the shells of molluscs is of much interest under the micro- scope. Usually the shell will he found to be made up of three separate layers of calcareous1 matter. The outer layer is very thin and often rough and of a brownish, or dark gray, color, the middle layer is much thicker and dull white; while the inner layer is usually pearl- like in color. If you will examine a section of the middle layer you will find that it has a honeycomb ap- pearance and is made up of a large number of prismatic2 cells which are hexagonal, that is, six-sided, in shape. This structure is de- posited by the outer skin, or epidermis, that has been given its crystalline form by suc- cessive deposits of calcium carbonate inside the cells of which it is composed. The inner layer of the ordinary shell is known as mother-of-pearl, or nacreous layer, it has an irridescent luster which is caused by the pecu- liar texture of the surface due to the numerous surface layers, or laminae.3 In the pearl oyster, or to give it its scientific name, Melea- grina Margaritifera, the pearl is formed as fol- lows: a particle of foreign matter, such as a grain of sand, gets into the shell and acts as an 1 Made of calcium carbonate, that is, limestone. 2 Having the colors of the rainbow. 3 Plural of lamina. 156 BOOK OF THE MICBOSCOPE irritant to the oyster. A layer of nacreous matter, like the inside layer of its shell, then begins to form, or concrete around the foreign matter, and in this way the pearl is built up layer on layer. The Gastropods belong to the family of mol- luscs and include the snails and slugs. The tongue, or palate, of a Gastropod is a wonder- ful object under the microscope, and while it is called a tongue it is unlike that of any other animal. It consists of a short tube which is split open at its upper end and spread out on the floor of its mouth; the inside of this tube is studded with teeth, as shown in Figure 44, and these range in number from 100 to 20,000 ac- cording to the species. In some Gastropods such as the whelk,4 which has a whorled shell, that part of the toothed tube which rests on the floor of its mouth is provided with protractile5 and retrac- tile6 muscles, and these enable it to be used as a drill with which the whelk bores through the hard shells of the other molluscs it feeds upon. Fig. 44.—Arrangement of Teeth in the Palate of a Gastropod * A gastropod ■which burrows in the sand and preys on clams and other bivalves. B Muscles which extend or push out something. •Muscles which pull in. HIGHER ANIMAL SPECIMENS 157 A peculiarity of this arrangement is that the teeth can also be raised or lowered at will, and as fast as the old teeth are worn out they are replaced by new ones. More interesting yet is the development of the embryo7 of the Gastropods which lay the eggs from which the embryo is hatched. In some species, such as the seasing, the number of these eggs is upwards of a half million, they are very small when first laid. As the eggs are quite transparent you can easily watch the changes that take place in the formation of the embryo in them. These eggs are deposited in masses and are distributed throughout a jelly- like substance which is found attached to the surface of the various seaweeds and polyps. The first change to take place inside the egg after fertilization is the splitting, or segmenta- tion as it is called, of the material so that there are two equal cells, just as the Amoeba under- goes subdivision. Each of these in turn di- vides into two more cells and this process is carried on until a very large number of cells is produced, all of them remaining together in an irregular mass. Finally, a two-layered hollow structure results which is the Gastnda, and in time each one of these becomes an embryo, when the latter puts out a cilia Fringed lobe on either side of its anterior, or front end. About t The germ, or earliest development of a rudimentary animal. 158 BOOK OF THE MICROSCOPE this time the rudimentary organs of hearing, or auditory vesicles, as they are called, are formed but do not develope any farther. An extension also grows out from the embryo Cilia Ciliated Lobe Foot J_obe Mouthy Rudimentary hear- ing Organs or Auditory Vesicle Oesophagus Cloak or Body Membrane Intestine Stomach Shell Fig. 45.—Embryonic Stage of a Gastropod which in time becomes a muscular disk, or foot, and by means of this the adult can attach itself to rocks, etc. Next a shell gradually forms on and around the embryo, and soon after the egg case bursts and the embryo swims freely around by means of the ciliated lobes which serve to bring food to its mouth, as shown in Figure 45; later on these ciliated lobes disappear and the toothed tongue, or palate, begins to develop. You will also like to know about the pigment cells, or chromatophores, that are found in members of the cuttlefish and squid family; it is by means of these cells that the animal can change its color at will. They consist of cells HIGHER ANIMAL SPECIMENS 159 containing various particles of color, including some that are inky black, called melanophores, these are so made that they can take on either a globular, or a flattened and elongated form; in this way the density, or depth of color, can be changed. The Division of Arthropoda.—One of the largest phyla of the animal kingdom is named Arthropoda; it contains one order—the insects, or Insecta—of which there are probably over a million distinct species, although less than half of this number has been classified. You ought to be able to know the four general classes of Arthropoda when you see them; (1) the Arach- nida, which includes the spiders; (2) the Crusta- cea, which includes the crabs; (3) the Myriapo- da, which includes the thousand-legged worms, and (4) the Insecta, which includes flies, etc. The members of the Arthropoda division may be described in a few words as being articulated animals, by which I mean that they are made up of a number of segments, which in the typical Arthropoda are limited to twenty or less. They are bilaterally symmetrical, since to these seg- ments are attached pairs of jointed appenda- ges that are alike on both sides. These seg- ments are called somites and are hard, shell- like rings, or hoops, which are joined to each other by softer membranous tissues. The ap- pendages consist as a rule of (a) from one to 160 BOOK OF THE MICROSCOPE two pairs of feelers, called antennae; (b) from two to four pairs of jaws; and (c) upwards of three pairs of jointed, or articulated, legs. It is also interesting to note that (d) the eyes range from one to four pairs and that these are simple in spiders and compound in crabs and in- sects. The Arachnida, or Scorpions, Spiders, Ticks and Mites.—These Arthropoda have no anten- nae and a body that is made up of two parts only, namely (a) the cephalothorax,s and (b) the abdomen. They usually have six pairs of jointed appendages, two pairs of which are fixed to the head and serve to catch and hold their prey, while the other four pairs serve as legs. Most of these animals breathe by means of trachae, or air tubes, and takes in the necessary air through spiracles, or breathing pores in the body. The Arachnida are divided into ten or- ders of wrhich the following are the most im- portant: (1) Scorpionidae, or scorpions; (2) Araneida, or spiders; and (3) Acarina, or mites and ticks. The Crustacea, or Crabs, Lobsters and Shrimps.—The members of this division are very like that of the Arachnida in that the body is composed of only two parts, that is, the ceph- alothorax and the abdomen. Their character- istic feature is the protective shell, or carapace, 8 This means a united head and thorax. HIGHER ANIMAL SPECIMENS 161 as it is called, with which they are covered and which is secreted by the skin and impregnated with calcium carbonate deposits. In most of the orders of Crustacea this shell consists of segments and forms a protective coating over the appendages as well as over the body proper. There are two main divisions of Crustacea that you should get clear in your mind: (1) Entomostraca, which include the smaller and more lowly organized forms, such as water fleas and barnacles; and (2) Malacos- traca, which include the larger and more highly organized forms, such as the lobster, crab, shrimp and crayfish. Myriopoda, or Millepeds.—These curious jointed animals are known by their long worm- like bodies which, usually, have some of the seg- ments fused together and have a length of from two to 18 inches. Each segment has one or two pairs of appendages attached to it and as the segments number from 10 to 50 you can easily guess how these many-legged animals come to be called millepeds. There are four orders of Myriopoda, the two important ones being (1) the Chilopoda, or thousand-legged worms; and (2) Symphyla, or centipedes. You can easily tell them apart be- cause, as I mentioned above, the first has two pairs of legs attached to each segment and the latter only one pair to a segment. It is in this 162 BOOK OF THE MICROSCOPE latter order that the poisonous kind is found, the first pair of legs being fused at the base so as to form a poison sac. The Insecta, or Insects.—Finally there is the great class of Arthropoda known as Insecta; this includes all the true insects. The members of it are characterized by having three separate and distinct body parts: (1) a head; (2) a thorax or middle part; and (3) an abdomen, or that part containing the digestive organs. There are, moreover, attached to the thorax one or two pairs of wings in the winged order and three pairs of legs. If you will examine the head of a typical in- sect you will find that there are four pairs of jointed appendages, namely, the antennae, and the mouth parts, or mandibles and maxillae, as they are called. An examination of the thorax will show that the segments are usually fused together where the wings are joined on to hold the powerful wing muscles. The body is pro- vided with spiracles, and the insect breathes through these and the trachea. The true in- sects are fitted with compound eyes which will be described presently. Since there are upward of a million species of insects their classification is bound to be more or less complicated, but it is based on two well-defined features which are distinctive in the larger number of species, namely. HIGHEB ANIMAL SPECIMENS 163 whether the insect is (a) wingless, or (b) winged. The first kind is known as Apterygota and the second as Pterygota (pronounced Ter- i-go-ta). The Apterygota, or wingless insects, include two suborders which are (1) Thysanura, or bristletails, and which are often called fishmoths owing to their resemblance to moths; and (2) Collembola, or springtails, owing to the very curious springlike caudal appendage which they have. The Pterygota is further subdivided so that members of it can be identified into two kinds: (a) Heterometabolous, or insects whose young, or nymphs, as they are called, pass through a very slight metamorphosis9 or none at all; and (b) Holometabolous, or insects whose young go through a complete metamorphosis. The Parts of an Insect—The Integument.— Now suppose you look a little closer into the structure of insects; this is easy to do because you can get all the specimens you want right at hand. In dissecting any typical insect so that you can examine it under the microscope, you will see that its body is covered with a sort of hardened skin, or integument. This horny casing is composed of an animal substance known as chitin which may be strengthened by deposits of mineral matter. 8 Passing of one form or shape into another. 164 BOOK OF THE MICROSCOPE The Appendages and Other Structures.—In- sects are provided with numerous interesting structures, such as (1) the scales, or plates, (2) the hairs, (3) the antennae, and (4) the legs and feet. Scales are found on both surfaces of the wings of many insects, particularly in those of the moth and butterfly tribes. These scales are often brilliantly colored, and in moths and butterflies this color is due to the structure of the scale which is made up of two or more layers of membrance with a layer of pigment be- ween them. In beetles, however, the color of the scales is due to the extreme thinness of the membrane- layers, which reflect light just as the film of a soap bubble does. Many insects and their young, one stage of which is the larva, are covered with hairs as, for instance, the bee and the caterpillar. These hairs are usually formed, as you will clearly see with your microscope, of (a) a long rodlike shaft around which (b) spiny whorls are set. Mounted on the tip of the whorl is a circle con- sisting of six or seven large filaments which are knobbed at their free ends, the smaller end being attached to the tip of the hair. Rib* Pedicle. Fig. 46.—The Scale oe a Butterfly HIGHER ANIMAL SPECIMENS 165 Nearly all insects have antennae, or feelers; these consist of one or two pairs of jointed ap- pendages which start from the upper part of the head. These feelers differ greatly in various species, and are sometimes unlike even in the male and female of the same species, and hence they are very useful as a means of classifica- tion. If you examine the feelers closely, you will find inside the horny integument of many species a complete set of organs by means of which the insects are be- lieved to be able to hear. The legs and feet of the insects are also very interest- ing microscopic objects. The leg, as a rule, consist of five segments, the feet are pro- vided with hooked claws and, in most insects, with adhe- sive pads by means of which they adhere to the objects they happen to light on. The Head Parts.—Next examine the head parts. These are wonderfully made. The eyes are located in the upper part of the head and are compound, that is, they are made up of hundreds, and in some species thousands, of will find inside the horny integument of many separate little eyes, or conical acelli, as they are Knobbed Filaments Shaft Spiny Whorls Fig. 47.—Hair of a Beetle under the Microscope 166 BOOK OF THE MICROSCOPE termed, each of which is connected to the optic nerve. The mouth parts are another means of classi- fication ; insects usually have what is known as a mandibulate mouth; this is made up of (a) mandibles, or main jaws, which are fitted with formidable teeth in some species; (b) the maxil- lae which are a second pair of jaws that set just below the mandibles and with which the insect carries the morsel of food to the back of its mouth; (c) the labrum, or upper lip; and (d) the labium, or lower lip. The labium is often elongated so that it forms the tongue of the bee, and the proboscis of the fly. The Body Parts.—In dissecting the body of an insect you should first of all examine the esophagus, which leads from the mouth to what is commonly called the gizzard. This organ is lined with several rows of teeth; these reduce the particles of food it eats into a digestible state. The blood, which is colorless or brown- ish red, is kept in circulation by a dorsal vessel, which serves as a heart. The construction of the respiratory apparatus of an insect consists of trachece or air tubes, as I have described before. Your microscope will show you that these tubes pass into every part of the body, even into such minute parts as the labium. The spiracles through which the air is drawn into the tracheae are on the HIGHEE ANIMAL SPECIMENS 167 sides of various segments, and are provided with a sort of sievelike membrane over their openings in order to filter the air before it is passed into the trachea system. In some insects the last two segments of the abdomen are equipped either with (a) a sting, or (b) an ovipositor. The sting consists of a pair of darts that are projected from their Filter Mem brane Border erf Spiracle Fig. 48.—The Spiracle of an Insect sheaths, which latter is formed of an extension of the skin of the last segment, by means of powerful muscles located at their roots. An irritating liquid is secreted at the base of the sting. The ovipositor is a device by which some insects deposit their eggs. It is formed of a long tube in which the eggs are carried, and which, like the sting, is sheathed in the last segment. It is also provided with powerful retractile and protractile muscles, and usually has a toothed, or serrated, edge so that it can be used as a boring tool, with which it bores a hole to lay its eggs in. 168 BOOK OF THE MICROSCOPE Reproduction of Insects.—In most insects reproduction is carried on in this fashion: the sexual cells of the female are fertilized by those of the male; and these fertilized eggs are laid in some receptive place, where they shortly hatch into larvae, which are maggotlike little animals. As these grow larger the skin hardens and forms a protective covering over the body; when in this state the young are known as pupa. A complete change in the form, structure and tissues of the pupa takes place, known as meta- morphosis, during which the young insect is developed in the body of the pupa after which the shell drops off. CHAPTER XII HIGHEST FORMS OF ANIMAL SPECIMENS UNDER THE MISCROSCOPE After you have examined the simpler struc- tures of the lower animals as directed in the foregoing chapters, you will he prepared to take up the great subphylum of the highest type of animals known as the Vertebrata, that is, ani- mals with backbones. The Vertebrata, or Animals with Back- bones.—This subphylum comprises all the higher animals, including the highest of all, which is man. The outstanding features of these animals, which are called Vertebrates and which separates them from those we have just examined, is that they have a backbone; in the higher orders this forms the main support for the rest of their articulated bony structure, or skeleton. The vertebrate, or backboned, animals dif- fer also from those which are lower in the scale of life in that they are provided with highly complex and well-developed organs which per- form all of the functions to maintain life; and 169 170 BOOK OF THE MICROSCOPE (2) the complex network, or system, of nerves; which lead from the brain into all parts of the body and control the various organs. The great subphylum of the Vertebrata includes all of those animals that we know best; it has been divided into six chief classes: (1) Cyclostomata, or lamphreys; (2) the Pisces, or true fishes; (3) the Amphibia, or frogs, salamanders, etc.; (4) theReptilia, or reptiles; (5) the Aves, or birds, and (6) the Mammalia, or mammals. These classes are further divided into numer- ous orders, and each of these again into fami- lies, genera and species. Now let us take a brief look at each one of the classes above named and find out what their main order are and perhaps a few of their distinctive features. The Cyclostomata, or Lamphreys and Hags.— These are the lowest of the vertebrate animals and, indeed, they do not even have the true backbone of the higher animals, but instead a mere rod of cartilage,1 the skull itself being of a cartilaginous nature rather than a bony structure; this is also true of some fishes, such as the sturgeon, of which they are the fore- runner. The Pisces, or Fishes.—This class is divided into twTo groups; (1) the Chondropterygii (pro- i A semi-transparent elastic tissue that forms most of the skeleton of embryos and the very young of the backboned ani- mals which in the higher animals changes into bone. It is com- monly called gristle. HIGHEST ANIMAL SPECIMENS 171 nounced Kon-drop'-ter-y"-i-i) which are fishes with soft skeletons; and (2) Teleostomi (pro- nounced Tel-e-os'-to-me") which are fishes with hard skeletons; of the latter there are about 10,000 species, including all the well-known kinds. All fishes are characterized by their peculiar bony structure, streamlike bodies and gills which peculiarly adapt them to living in the water. The skeleton of the fish is provided with fins which serve the double purpose of keels and rudders, the caudal, or tail fin being the chief rudder. The mouth has long jaws set with teeth. The ribs, which are fixed to the backbone, act as a protective structure for the heart, stomach, intestines and other vital organs, while the breathing apparatus consists of gills; these extract the necessary oxygen to support life from the water. The Amphibia, or Frogs, Toads and Salaman- ders.—This class of backboned animals is just between the reptiles and the fishes. They are characterized by the young having gills which disappear and are supplanted by lungs in the adult of some species. There are three main orders of amphibia: (1) the Apoda, or worm- like animals that have no limbs whatever and which are found in tropical countries; and (2) the Candata, or those animals which are long tailed and have two sets of limbs, such as the 172 BOOK OF THE MICROSCOPE salamanders and newts; and (3) Salientia, or tailless amphibians which have two sets of limbs, such as frogs and toads. The Reptilia, or Reptiles.—This class includes not only snakes but other animals which we do not ordinarily think of as reptiles, such as turtles, alligators, crocodiles and lizards. Now there are three chief orders of reptiles; (1) Testudinata, or turtles of both the land and sea varieties; (2) Crocodilini, or alligators and cro- codiles; (3) Squamata, or lizards and serpents; all of which lay eggs. The Aves, or Birds.—Now while we do not usually think of birds as animals they are just as much so as any other living creature, and it is well known that they have been evolved from reptilelike animals.2 There are two subclasses of birds; (1) the Archaeornithes, or fossil birds; and (2) the Neornithes, or modern birds. As a matter of fact the Archaeornithes, or fossil birds, have no place in this book because you are examining only living animals, or, more strictly speaking, very small sections of living animals where these are of the higher kinds. But because the Archaeopteryx (pronounced Ar"-ke-op'-ter-ix) is the sole representative of the true bird that lived in the dim and distant past, and from which was evolved the beauti- 2 These were the bipedal dinosaurs who walked more or less upright on their hind feet and had a homy bill, or beak. HIGHEST ANIMAL SPECIMENS 173 ful plumed and singing birds of to-day, I can- not help but include it here as a matter of gen- eral interest and knowledge. This early bird has come down to us as a fossil, or rock-em- bedded skeleton, which shows that it had teeth and a long tail like a reptile, but it also had feathers and could fly. The Neornithes, or modern birds, are short- tailed animals and have no teeth. There are two subdivisions of them, namely, (1) the Rati- tae, or running birds; and (2) the Carinatae, or flying birds. The first named include the ostriches, ernes and rheas. The distinctive feat- ure of these birds is found in the breastbone, or sternum, as it is called, which has no keel, and as a consequence there is no place for well- developed wing muscles. The last named in- clude all the living species that fly and of these there are over 13,000. Different from the Ra- titae they have a well-developed keel which in the flesh is filled out with powerful wing mus- cles. The Mammalia, or Mammals.—Finally you have reached that great class of vertebrate ani- mals which are known as Mammalia, or, as they are more easily called, mammals. These in- clude not only the largest animals but those whose complex structure places them highest in the scale of animal life. All mammals are pro- vided with mammary glands which secrete a 174 BOOK OF THE MICROSCOPE fluid that we call milk, by means of which the young are supplied with nutriment until they are old enough to eat solid foods. While there are some eighteen separate and distinct orders of mammals, there are only seven that you need to know about; these I have named in the order of their scale of life begin- ning with the lowest: (1) the Marsupialia, or Kangaroo and Tasmanian wolf; (2) Cetacea, or whales and porpoises; (3) the Ungulata, or hoofed animals; (4) the Rodentia, or gnawing animals; (5) the Chiroptera, or bats; (6) the Carnivora, or beasts of prey; and (7) the Prim- ates, or monkeys and apes, and man. The Marsupialia, or Kangaroos and Tasma- nian Wolf.—The distinctive feature of these animals is the pouch, or fold of skin on the ab- domen, in which they carry their young after the latter are born. The Cetacea, or Whales and Porpoises.— These animals, you will observe, belong to the order of mammals and not to that of the fishes. They are known by their lack of teeth; are warm-blooded, and suckle their young. Like the fishes, however, they have streamlike forms and live in the water. The Ungulata, or Hoofed Animals.—In this order are included all the true hoofed animals; they have from two to five toes coated with a thick horny skin, or epidermis. The Ungulates HIGHEST ANIMAL SPECIMENS 175 are subdivided into groups which have (u) an even number of toes, and (b) an odd number of toes. The latter have four-chambered stomachs and can swallow their food without chewing it; it passes into the first two of these chambers; here it is softened; then it can be returned to the animal’s mouth for mastication, that is, chewed, at leisure. This process is called ruminating. Deer, cattle and all animals that “chew the cud” are known as ruminants. The Rodentia, or Gnawing Animals.—These are mammals such as the beaver, rabbit, rats and mice, and all are characterized by their sharp, chisel-like front teeth which are adapted for gnawing. This is the largest known order of mammals and includes twenty or more fami- lies and several thousand species. The Chiroptera, or Bats.—The bats are the only order of mammals that have the power of flight. They have wings formed of thin mem- branous tissue and are almost as much at home in the air as the birds are. It is a prevalent notion that bats are blind, but they have very good eyes and exceptionally good ears. The Carnivora, or Beasts of Prey.—To this great order belong such mammals as cats, dogs and all other hunting and meat-eating animals, or animals that are carnivorous, as they are called. They are distinguished by their teeth, 176 BOOK OF THE MICROSCOPE strength, litheness, and the mechanism of their claws, all of which are suited to their preying insticts. The Primates, or Monkeys, Apes and Man.— These mammals are the highest in the scale of animal life and all of them are very much alike in their general structure. The accepted theory of the evolution of man, the highest primate of all, is that he came from an ancestor that was common alike to him and monkeys and apes. In this connection it is interesting to note that man who originated in the Old World and all Old World monkeys have 32 teeth. Like man the monkeys require nearly a year to produce their young, and the female of the species pro- duce hut one or two offspring at a time. The Structures of the Higher Animals.— Having now a general idea of the different sub- divisions of vertebrated, or backboned, animals you are ready to take up the various structures of their many parts; to do this you must dis- sect them and mount the minute sections so that you can examine them with your micro- scope. The Cells and Fibrous Structures.—All of the higher animals, including man are built up of two kinds of structures, (1) cellular tissue,3 and (2) noncellular, or formed material. 3 By tissue is meant an aggregate of cells, together with the substance that is in between them which form one of the materials of which a plant or animal is constructed. HIGHEST ANIMAL SPECIMENS 177 The cellular tissue consists of cells which are able to transform materials taken from the blood of the animal into the same material of which are composed, or into a product which they can further expand. In other words, these cells make up the living and growing units of the body tissues. Now these cells are quite like the cells of the amoeba4 in structure and composition; they have a definite cell wall that incloses the contents of the cell, which is protoplasm; they contain a nucleus which plays an important part in the building-up, or formative power, as it is called. The fatty tissues, muscular tissues, nervous tis- sues, connective tissues are illustrations. The development of the cells, or the multi- plication of them, takes place by means of sub- division in much the same way that has already been described in connection with lower plant and animal organisms. The formed material mentioned above, such as the fibrous5 tissues of the body, is incapable of increasing itself because it consists of dead organic or mere inorganic6 deposits. These fibrous tissues serve to bind the other parts of the body fabric together and the skeleton, or bony structure, is formed of these tissues which 4 See Chapter IX. 5 Containing or consisting of fibers. 6 Any kind of matter that is composed of neither plant nor animal matter. 178 BOOK OF, THE MICROSCOPE have been strengthened by calcareous7 deposits. The bony structures are built up as follows: the cells, called bone cells, which form their basis are connected by extensions which pass between the fibrous tissues and form a network. These radiating canals are pathways for nour- ishing material, and for nerves in the bony structure; they are further described in the next section. The Structure of Bone and Teeth.—If you will examine a lengthwise section of a long round bone, or a parallel section of a flat short bone under a low power, you will see that it is traversed by many canals, which are known as Haversian canals, after Havers who discovered them. These canals run in the same direction as the length of the bone and are filled with an oily marrow just as the large central cavity of the bone is; further, you will see that the canals are connected by a network of cross branches. Now place a cross section of the same bone under a high power and you will see that each of these canals, which look like a little tube, is the center of rings of bony tissue arranged around the Haversian canal. These rings are made distinct by dark oval spots, or lacunae,8 as they are called; these are cavities in the bony structure which contain the bone cells with tu- 7 This means calcium carbonate, or limestone. 8 This word means spaces between the cells. HIGHEST ANIMAL SPECIMENS 179 bules that radiate inwardly from them to the Haversian canal, and outwardly from them to circumference of the bony rings; these tubules, which are shown in Figure 49, are called canali- culi.9 Lacunae ■Canaliculi -Haversian Canal Fig. 49.—A Typical Bone Structure The purpose of these canaliculi has already been explained, namely, to keep the bone cells in the lacunae in touch with the walls of the surrounding blood vessels from which they get their nourishment. You can tell from the size and shape of the lacunae whether the bone be- longs to a mammal, a bird, a reptile or a fish, since those of mammals are shorter in length and smaller in breadth than those of birds, and those of reptiles are very long and narrow, while those of fishes are angular in shape. 9 Evidently meaning little tubes. 180 BOOK OF THE MICROSCOPE The structure of the teeth of the lower ver- tebrates is very like that of bone which I have just described except that the canaliculi do not pass into the lacunae. In the higher verte- brates the center of the tooth is a single large cavity from which the canaliculi radiate toward the outer sur- faces. The upper sur- face of the tooth is covered with enamel, the inner part is composed of dentine (see Figure 50), which is a bonelike sub- stance. The enamel is made up of long prisms resembling those of prismatic shell substances found in some of the lower shelled animals. The Structure of the Dermal10 Skeleton.—In a large number of orders, such as Reptilia (rep- tiles) and Pisces (fish), and even in some mammals, such as Armadillo, the skin is rein- forced, or covered, by scales and plates which usually consist of a horny, or bony, texture and in some cases are even enamel-like. In general, however, these scales, or plates, overlap each other as fish scales do, but they Enamel Dentine Cavity -Cement Fig. 50.—A Section Taken THROUGH A HUMAN MOLAR 10 Of or pertaining to the skin. HIGHEST ANIMAL SPECIMENS 181 are very different from those of reptiles for they are developed in the substance of the skin itself and are cartilaginous11 in texture; fur- ther, they are often covered with a layer of epi- dermis, or true skin. In reptiles, however, the scales are formed on the surface of the true skin and are classed with the other epidermae, or skin, structures of backboned animals. These structures are (1) the scales and plates of rep- tiles; (2) the hairs of mammals; (3) the feath- ers of birds; and (4) the hoofs, nails, claws and horns of vertebrates in general. The scales and plates of reptiles are formed on the surface of the skin and are composed of aggregations of greatly flattened cells which, in turn, are built up of horny matter. The hairs of mammals are only a modification of the scale structure just described. If you will examine a hair with your microscope you will see that it consists of two elementary parts which are (1) a corticalf2 or investing,13 substance that is made up of flattened scales in some animals and spheroidal14 cells in others; and (2) a me- dullary, or pithlike, substance which is of a much softer texture than the cortical that surrounds it. This is formed of rounded cells in some cases Of or like cartilage. 12 An external substance. 13 To cover or envelop. 14 This means a figure that is like a sphere, but which is not spherical, that is, round like a ball. 182 BOOK OF THE MICROSCOPE and polygonal, that is, many-sided cells, in others, as shown in Figure 51. The feathers of birds are really only hairs on an enlarged or slightly more complex scale, the quill corresponding to the bulb, or root, of the hair, and the horny outer part, or barrel of the quill, corresponds to the cortical substance of the hair. The nails, hoofs, claws and horns of mammals are further modifications of the hair structure, for, when a section of any of them is examined under the microscope, you will find it to be made up of a number of little tubes that have the same kind of a cell structure as hairs have when the whole is formed into one piece. The Skin.—The next step is to examine the skin of animals, particularly that of mammals. A vertical section of the skin will show under your microscope that it is made up of (1) the cuticle, or outer layer of the epidermis; (2) the perspiratory ducts, which perforate the outer layer, and also lead into a deep layer, of epi- dermis, or Stratum Malpighii, as it is called, and which separates the epidermis from (3) the cutis vera, or true skin in "which (4) the -Rounded Cells Scales or "FlattenedCells Fig. 51.—A Longitudinal Section of an Animal Hair Showing Struc- ture HIGHEST ANIMAL SPECIMENS 183 sweat glands are embedded, their ducts leading up through the epidermis. In the open cavities and canals of the body, such as the mouth and nose, the skin no longer has a tough cuticle, but instead takes on a mem- branous form of which there are two kinds, called the mucous and serous membranes; a thin protective fluid which is secreted by the glands in them is spread over their surface, which keeps them from being irritated and dry- ing up. Structure of the Glands.—All of the necessary secretions of the body, such as the bile of the liver, the saliva of the salivary glands, and the nutritive fluid of the mammary glands, by which the young are nourished, are produced by or- gans which are constructed on one general principle. These glands consist of minute fol- licles, or bags, which are filled with spheroidal cells. These cells as they develop draw into them whatever is in the blood that it is their purpose to secrete, and then discharge it into the cavity of the organ whence it is carried away by ducts or the blood stream. The Structure of the Muscles.—The muscles of animals are made up of a number of fasciculi, which are bundles of fibers that lay side by side and are united by a connective tissue. Your microscope will show that they consist of two 184 BOOK OF THE MICROSCOPE kinds, (1) striated fibers, and (2) nonstriated fibers. In the striated kind, the fibers are shaped like flat wavy ribbons with cross lines on them; and are found in those muscles of the body where quickness of movement is needed. The non- striated muscular fibers are found in the walls of the stomach, intestines and bladder where less rapidity of movement is required; these consist of flattened, twisted ribbons without any cross lines which do not lay parallel with each other as in the striated kind, but are interlaced instead. The Structure of the Nerves.—The nerve cells of vertebrate animals are of two different kinds: (1) an ordinary cell without any long processes that goes to make up the ganglionic centers, and (2) a cell with very long processes which forms the nerve trunks. In their typical form the nerve cells of the ganglion are glob- ular in shape; these cells, however, are often slightly elongated, so as to take on the long form. All nerve cells are made up of fine gran- ular protoplasm, the nucleus being found in the spheroidal part of the cell. The nerve fibers of which a nerve trunk is made consist of a thin membranous sheath sur- rounding a thicker soft layer, called the white substance of Schwan, after the man who dis- covered it. This is a white protoplasmic sub- HIGHEST ANIMAL SPECIMENS 185 stance intended to protect the innermost part, which is called the Apis Cylinder. The latter is the vital part of the nerve fiber. Some of the nerve fibers, however, such as those found in the olfactory nerve, that is, the nerve which enables yon to sense, or smell, an odor, do not have the white substance, and are called non- medullated nerve fibers. The Blood.—It is the blood of vertebrate ani- mals that furnishes the tissues with the nutri- ment they need; it is made up of isolated float- ing cells of which there are two kinds: (1) red corpuscles, and (2) white corpuscles. The red corpuscles are always in the shape of flattened disks in man and other mammals, while in birds, reptiles and fishes they are oval. These red corpuscles consist of flattened cells whose walls are not different from the cell con- tents, although the nuclei are absent in the mammals. They contain hemoglobin,15 the red coloring matter of the blood. There are about five millions (billions, if the old system is used) of these red blood corpuscles in a cubic milli- meter16 of human blood, each one of which is about 0.008 mm. in diameter. These red cor- puscles have a definite and distinctive size in every order of animal, and even in different 15 This is composed of hematin and globin. 16 A millimeter equals about 1/25 of an inch; in other words, 1 inch = 24.4 millimeters. The abbreviation is mm. 186 BOOK OF THE MICROSCOPE species of the same order. The smallest are those of a mammal called the Javan chevrotain, which measure only 0.002 mm. in diameter, while the largest belong to the Proteus, a mem- ber of the frog tribe, and measure 0.063 mm. in diameter. The white corpuscles are much smaller than the red corpuscles (see Figure 52), and are much fewer in number being only 6,000 to the cubic millimeter of blood in man. They are usually globular in shape and have a prominent nu- cleus. The Circulation of the Blood.—One of the most interesting and instruc- tive things that you can do with your micro- scope is to watch the circulation of the blood of some living animal as it courses through the capillary blood vessels, by means of which it is distributed to the tissues which derive their nourishment from it. A frog is a good animal for this purpose, and you should have a frog hoard. This consists of a piece of wood % inch thick, 21/2 inches wide and 8 inches long, with a hole % an inch in diameter in the middle and about l1 inches from one end, as shown at A in Figure 53. Now take your live frog, wrap him in a strip of wet Red Corpuscles .White Corpuscles Fig. 52.—How the White and Red Corpuscles in the Blood op a Frog Look HIGHEST ANIMAL SPECIMENS 187 muslin, then lay him on his back on the board and keep him there with a couple of rubber bands slipped around him and the board. Fig. 53A.—How the Frog Slide Is Made Draw one of his legs down until the webbed part of the foot comes over the hole in the board; next tie a stout piece of thread to each of his toes and then stake them out by means of pins driven in the board so that his toes will spread as far apart as they can comfort- Uj co 3 \r- Frog Stage Fig. 53B.—The Frog on the Slide ably go, as shown at B. Then wet the web of his foot with a little water, and place the end of the board on the stage of your microscope and clip it securely with the spring clips; you are now ready to bring his foot into the field and to focus it, using a power from 75 to 100 188 BOOK OF THE MICROSCOPE diameters. You can now see the blood coming through the veins and the network of capilla- ries ; this is due, of course, to the driving move- ment of the frog’s heart as it beats. You will •Branch of Artery of \ Vein, Artery or Vein Pigment 6 Cell Pig. 54.—Circulation of Blood in a Frog’s Foot also see that, while the red corpuscles move along at a rapid rate through the center of each tube, the white corpuscles move more slowly and close to the walls of the capillary tubes as shown in Figure 54. CHAPTER XIII ROCK, MINERAL AND METALLIC SPECIMENS Up to this time your work with the microscope has been confined to one kind of matter only, that is, living, or organic matter; as you have seen, this consists of plant and animal life. There is, however, another great kind, or class, of matter that is found upon and in the earth’s crust—in fact the earth itself is for the most part made of it—and hence it is of the great- est importance to man in his everyday life. This class is called inorganic matter since, unlike organic matter, it does not have the power to propagate itself, that is, multiply and grow. Or to say it in another way it is nonliving matter. What Inorganic Matter Is Made of.—Inor- ganic matter in general is made up of a com- bination of two or more substances, each of which is of such a kind that it cannot be fur- ther separated, or decomposed, into other sub- stances by any known process, chemical or otherwise. Such fundamental substances are called elements; of these there are two kinds, 189 190 BOOK OF THE MICROSCOPE or classes, (1) the metals, and (2) the nonmet- als. What the Metals Are.—Iron, copper, lead, zinc, tin, aluminum, silver, gold and platinum are some of the elements that are known as metals. When the oxids of metals are acted on by water the hydroxids, or bases, of the metals are formed, that is to say, when the oxids of metals combine with water they form alkaline solutions. While a few of the above-named metals are found free in nature, that is, in their pure state, most of them are combined with other substances. What the Nonmetals Are.—All other ele- ments, that is, those which are not metals, are called nonmetals; these include the gases, such as oxygen, chlorine, fluorine, bromine, iodine, etc., and such solids as silicon, carbon, phos- phorus and sulphur. This is not a list of all the nonmetals by any means, but simply a few of the most common ones that are found in rocks and minerals. The oxids of the nonmetallic elements when acted on by water form acid solutions; this chemical property distinguishes them from the metals. A few of these nonmetals are found in the free state in nature; chief among them are the oxygen in the air, carbon in coal, in graphite and in the diamond, and sulphur, which is found free in most volcanic regions. ROCKS, MINERALS, METALS 191 While the metals do not combine chemically with each other, they combine readily with the nonmetals which also combine readily with other nonmetals. Compounds so formed are known as metallic, or nonmetallic, depending on whether a metal is or is not present. What Rocks and Minerals Are.—Rocks and minerals are composed of various substances, the former usually having little or no metals in them and the latter having one or more metals mixed with the nonmetals. You should, therefore, know something of the principal com- pounds which are formed in this way. What the Sulphides Are.—When a metal com- bines with sulphur a compound is formed that is called sulphide, and thus we have such min- erals as zinc sulphide, or sphalerite to give it its mineral name; lead sulphide, or galena; cop- per sulphide, or chalopyrite; iron sulphide, or pyrites, etc. What the Oxides Are.—When a metal or a nonmetal combines with oxygen, a compound is formed that is called oxide. Thus when iron combines with oxygen, iron oxide is formed; this is commonly called iron rust. Minerals that are oxides are quartz, or silicon dioxide; hematite, or iron sesquioxide; cuprite, or cop- per oxide; etc. What the Halides Are.—The nonmetallic gas- eous elements called chlorine, bromine, iodine 192 BOOK OF THE MICROSCOPE and fluorine are known as the halogens, and when these combine with the metals' they form substances called halides, that go by the name of chlorides, bromides, iodides and fluorides; thus the mineral halite is sodium1 chloride, that is, common table salt; the mineral fluorite is calcium2 fluoride, etc. What the Carbonates Are.—Carbon combines very easily with oxygen and when it does so carbon dioxide is formed. This is a nonmetallic compound and when this combines with a met- allic compound minerals that are called carbon- ates result, as for instance, calcite, which is cal- cium carbonate; cerussite, or lead carbonate, etc. What the Silicates Are.—When silicon3 and oxygen combine they form silicon dioxide, which is a nonmetallic compound, and, when this com- bines with some of the metals, a group of mi- nerals known as the silicates is formed; to this group belongs most of igneous, or fire-formed rocks, such as granite, since great heat is needed to bring about this combination. What the Phosphates Are.—These minerals are compounds of the oxides of the metals with phosphorous, which is a nonmetallic element; 1 Sodium is a metal. 2 Calcium is a metal. s This is a hard, colorless crystalline compound which is found pure in many rocks and sands. ROCKS, MINERALS, METALS 193 they are usually the secondary products pro- duced by the alteration, or chemical change, which has occurred in other minerals. The min- eral known as apatite is one of the most com- mon forms and is the combination of calcium fluoride and the double oxide of phosphorus. What the Sulphates Are.—These minerals are formed in much the same way as the phos- phates and are secondary products. The chief sulphates are anglesite, or lead sulphate; bar- ite, or barium sulphate; and gypsum, or cal- cium sulphate. While there are a great many other groups and combinations of metals and nonmetals to form minerals these are the main ones which you ought to get clearly in your mind so that you will know what you are about in your examination of rock, mineral and metal- lic specimens. The Structure of Rocks, Minerals and Met- als.—All rocks, minerals and metals have one of two kinds of forms or structures: (1) the amorphous, and (2) the crystalline. The Amorphous Form.—Those elements and substances which have no definite internal form or structure are called amorphous. Carbon, when in the form of graphite, is amorphous, and so is sulphur under certain conditions. The Crystalline Form.—This form, or struc- ture, is definite and all of the minerals named above are found in this state as well as carbon, 194 BOOK OF THE MICROSCOPE which, as yon have just seen, is amorphous m graphite, and crystalline in coal and in the dia- mond. The formation of crystals of various substances and compounds is of great import- ance in microscopic work; you should therefore have a clear general idea of crystalline forms and their causes. Crystals and Their Systems.—The chief con- ditions under which compounds take on a crys- talline form are (1) when they pass from a gas- eous or a liquid state into a solid state, as, for instance, the crystals which are formed in iron when it cools from a liquid, or molten, to a solid state; and (2) the evaporation, or de- hydration,* of a chemical solution, that is, the removal of the water from the solution. Crystals are usually produced very slowly, and the outward form of a crystal is simply an enlargement of its interior structure, since it is built up by the growth of one layer upon an- other. There are six different kinds, or types or systems, as they are called, into which crys- tals form. These follow: The Regular or Isometric System.—In this system the crystals have three axes,5 all of which are of equal length and at right angles to each other, such as the cube as shown at A in Figure 55. This is the form that sodium 4 To deprive of water. 6 The plural of axis. ROCKS, MINERALS, METALS 195 chloride, which is common table salt, crystallizes in. The Square Prismatic System.—In this sys- tem, which is also called the tetragonal system, Fig. 55.—Characteristic Systems in Crystallization of Minerals the crystals are longer in one direction than in the others, and have either a four- or an eight- sided cross section and three axes that set at right angles to each of the other two, which 196 BOOK OF THE MICROSCOPE are equal in length as shown at B. Zirconium silicate crystallizes in this system. The Hexagonal System.—In this system the crystals are elongated in one direction and have either a three- or six-sided cross section and four axes, three of which are in the same plane, as shown at C. Marble crystallizes in this system. The Rhombic System.—In this system, which is also called the orthorhombic system, the crys- tals have a rhombic cross section, that is, they have three axes all of which are of unequal length and at right angles to each other as shown at D. Sulphur often crystallizes in this form. The Mono symmetric System.—This is also called the monoclinic system. The crystals of it have three axes of unequal length, two of them being at right angles to each other as shown at E. Gypsum crystallizes in this form. The Asymmetric System.—In this system, which is also called the triclinic system, the crystals have three unequal axes, none of which are at right angles to one another, as shown at F. Copper sulphate crystallizes in this form. It will be well worth your while to get the above systems of crystals clear in your mind; when you do so you will find that, with the aid of your microscope, you will have no great ROCKS, MINERALS, METALS 197 trouble in identifying any that yon may have occasion to examine. The Polarization of Light.—-As yon have al- ready learned in Chapter III, light travels in the form of waves set up in the ether, and the wave front is always at right angles to the ray of light, which is made up of a large number of such waves, and is moving. You have also seen how certain substances, sueh as prisms of glass retard light waves and cause the light to be bent, or refracted, out of its course, and split up or dispersed, into its component colors. In a like manner certain substances such as calcite, or Iceland spar, as it is commonly called, have the property of dispersing the ray of light into two separate and distinct rays whose wave fronts advance in planes that are at right angles to each other; this phenomenon is known as the polarization of light. If these rays are now passed through a sec- ond prism, each of them will be refracted to a different degree, and if the refraction of one as against the other is great enough, you will see two separate and distinct images of the object. This is based on the same principle as the colors of light wave in a lens, all of which I have explained in Chapter III. What the Polamcope Is.—When two prisms of calcite, that is, Iceland spar, are cemented together with a layer of Canada balsam, the 198 BOOK OF THE MICROSCOPE double prism thus formed acts on a ray of or- dinary light like this: when the light is polar- ized, as explained above, one of the rays so formed passes through the two prisms un- changed; this ray is called the polarized, or extraordinary ray. The other ray of light, which is known as the ordinary ray, is very greatly refracted when it d Microscope standard, mounted on it to support a small camera. The latter can be turned around on the rod to align it with the microscope or turned out of the way when you want to examine the Fig. 71.—A Photomicrographic Outfit 234 BOOK OF THE MICROSCOPE object visually. A light-tight sleeve provides the coupling between the ocular of the micro- scope and the camera lens. For photomicrographic work you will find that sunlight gives the best lighting effects and that the camera must be arranged so that it will be free from all vibration. Further, you must take exceeding pains to focus the object sharp before photographing it, and you will find that a specimen which is formed of differ- ent structures will photograph better if it is stained. INDEX Aberration, 44 caused by different media, 44 chromatic, 31, 35 produced by cover glass, 44 spherical, 30, 35 Achromatic lens, 38 how made, 38 what it is, 38 Achromatic substage con- denser, 54 Adjustable objectives, 59 Adjustment, what change of, does, 42 Adulteration of foods, 218 Air mounts, how to make, 113 Alcohol, 122 Alcohol carmine, 118 Algae, 123 green, 123 low form of plant life, 121 Amoeba, 139 Amphibia, 171 Angiospermal, 132 Angiosperm fibers, 214 Angular aperture, the, 48 Animal foods, 221 Animals, 169 blood of, 185 Animals—Continued cells and fiberous struc- tures of, 176 examination of, 11 glands, structure of, 183 muscles, structure of, 183 nerves, structure of, 184 structure of higher, 176 the skin, 182 with backbones, 169 classes of, 170 Animate objects, 92 Annelida, 148, 151 Annelids, are oviparous, 153 Annelid worms, 152 Antennae, 162 Anther, 136 Antheridia, 130 Anthozoa, 144, 146 Aplanatic lens, how made, 34 Apterygota, 163 Arachnida, 159, 160 Archaeornithes, 172 Archegania, 130 Ares, 172 Arm, the, 51, 55 Armadillo, 180 Arthopoda, division of, 159 Articulated animals, 159 Artificial light, and use of condenser, 85 235 236 INDEX Artificial Light—Continued using, 71 Artificial silk, 212 Ascaris, 151 Asphaltum varnish, 113 Asymetric system, 196, 206 Auditory vesicles, 158 Axial, the, 79 Bacteria, 126 Balsam, as a mounting med- ium, 118 Balsam mounts, 116 Bamboo pole, 96 Base, the, 50, 51 Beale’s camera, 230, 231 Beasts of prey, 175 Beetle, hair of, under micro- scope, 165 Birds, 172 feathers of, 182 Blood, 185 circulation of, 186 Body tube, the, 51, 60 Bombyx mori, 211 Bone, structure of, 178, 179 Borax carmine, 118 Botany, 92 divisions of, 94 Bread, 220 Bristletails, 163 Butter, 220 Butterfly, the scale of a, 164 Calcareous matter, 155 Calcium carbonate, 147 Calyx, 135 Camel’s hair brush, use of, 68 Camera Lucida, 226 how it works, 228 the abbe, 227 what it is, 226 Capsule, 132 Carbonates, 192 Carbon dioxide, 122, 128 Carnivora, 175 Cassava, 218 Cedar oil, 47 Cells, 132 building up a, on a slide, 115 division of, in palmo- glaea, 122 Cellulose, 133 Cements, 113 Centerpedes, 161 Center stop, 81 Central light, 79 Cetacea, 174 Chemistry, the microscope in, 14 Chilopoda, 161 Chiroptera, 175 Chloroform, 67 Chlorophyll corpuscles, 121 Chromatic aberration, how caused, 31 how corrected, 35 meaning of, 31 Circulation of blood, 186 Clearing, 116, 118 Coarse adjustment, 51, 56 taking care of, 75 Coelenterata, 144 Coffee, 220 Collecting outfit, 95 Collembola, 163 INDEX 237 Color screens, 86 Compound microscope, 2 how it forms a magnified image, 40 how it works, 33 how made, 49 lenses of a, 39 parts of, 50 Concave lenses, 21 Condenser, 85 artificial light and the use of a, 85 cleaning the, 69 how illuminate object without, 80 how to center, 86 how to tell when out of center, 88 Conifers, 132 Conjugates, 123 diatoms a branch of the, 124 how conjugates is carried on, 123 Converging polarized light, 204 Convex lenses, 21 Corals, 146 Corn and rice starch, 217 Corolla, 136 Corpuscles, 185 Cotton, 209 Cotton fibers, 209, 213 Cover glass, 44 shifting effect produced by, 44 Crabs, 160 Crocodiles, 172 Crown glass, 37 Crustacea, 159, 160 Crystals, 194 analyzing, with Polari- scope, 202 and their systems, 194-197 how to identify all kinds of, 205 identifying by converging polarized light, 204 identifying by extinction angles, 203 Cuttlefish, 158 Cyclostomata, 170 Cytoplasm, 121 Dark ground illumination, 90 Daylight glass, 82, 86 Daylight, using, 70 Dehydration, 116, 117 Dermal skeleton, structure of, 180 Diatomaceae. See “Diatoms” Diatoms, 88 a branch of the conju- gates, 124 Disease, the microscope in, 12 Dispersion, how neutralized, 36 Dissecting needles, 101 Dissecting outfit, 106 Dissecting tools, 106 Doublet, a, 61 Doublet magnifier, the, 5 Drawtube, the, 51, 60 Dry mount, 113 238 INDEX Dry state, examining ob- jects in the, 103 Echinodermata, 146 Echinus, 147 Educational uses of a micro- scope, 9 Egg cells, 143 Embryo, 157 Enlomophthorales, 127 Ether, 74 Extinction angles, identify- ing crystals by, 203 Eye, the, 18 and light, 18 as a lense, 19 a section through, 19 the organ of sight, 18 Eyepiece, the, 39, 61 Fabrics, 207 Feathers, 182 Ferns, phylum of, 130 Filament, 136 Filicales, 130 Fine adjustment, 51, 57 care of, 75 Fingerprints, 74 Fishes, 170 Fishmoths, 163 Fixation, 116 Flax fibers, 207 Flea glass, the, 1 Flint glass, 37 Flour, 220 Flowering plants, 132 Flowers, structure of, 135 Focul length, finding, of a lense, 28 Focus, 72 getting, on work, 72 how it affects the image, 26 of a lens, 25 Foodstuffs, and their adul- terants, 215, 218 Footstalks, 130 Forceps, 107 Frog, blood circulation in a, 188 Frogs, 171 Frog slide, 187 “Frog spittle,” 121 Fronds, 131 Fungi, 126 Fungus, the sporange of mucor mucedo, 127 Fungus group, plants of the, 125 Gastropoda, class of ani- mals, 154 Gastropods, embryo of the, 157, 158 Gastrula, 157 Gelatine culture, preparing, 224 Germ incubator, 224 Germs, under a high power, 223 Glands, 183 Glycerine jelly, 116 Glycerine mounts, how to make, 115 Gnawing animals, 175 INDEX 239 Green algae, 123 Gymnospermal, 131 Gymnosperm fibers, 214 Hags, 170 Hair, animal, 182 Halides, 191 Health, the microscope in, 12 Hexagonal system, 196, 205 Hoofed animals, 174 Hydra, the, 145 Hydrocyanic acid, 218 Hydrogen, 122 Hydrozoa, 144 Image, 26 formation of a virtual, 27 how focus affects the, 26 how microscope forms an image, 40, 41 how virtual images are formed, 28 real and refracted, 24 Immersion, lens, 48 Immersion objective, 46 principle of the, 47 Index of refraction, 47 Indusium, 131 Infusioria, 141 Inorganic matter, 189 Insecta, 159, 162 Insects, 162 appendages and other structures, 163 body parts, 166 head parts, 165 Insects—Continued mouth parts, 166 parts of, 163 reproduction of, 167 spiracle of an, 167 Iodine, 122 Iris diaphragm, the, 54 Isometric system, 194, 205 Japanese lens paper, 66 Jelly fishes, 145 Joint, the, 51, 52 Kangaroos, 174 Kingdom, the, 93 Lamphreys, 170 Larvae, 148, 168 Leaves, 129 structure of, 134 Leeches, 152 Leguminous starch, 217 Lens, 28 how to find focal length of a, 28 the focus of a, 25 Lenses, 19 types of, 21 various kinds of, 20 Lens paper, Japanese, 66 Life slide, 102 kinds of, 103 Light, 17 action of lenses on, 27 action on minerals of pol- arized, 201 240 INDEX Light—Continued getting light on your work, 70 how a prism refracts, 23 polarization of, 197 softening the, 72 various rays of, 21, 22 Limestone, 147 Linen, 207 Linen fibers, 213 Linen tester, the, 5 Lining specimens, how to examine, 101 Lizards, 172 Lobsters, 160 Magnification of an object, how to measure, 230 Magnifiers, 96 kinds of, 4 what you can see with a, 3 Mammals, 173 Mandibles, 162 Margarine, 220 Marsupials, 174 Mastigophora, 141 Maxillae, 162 “Mayer’s Albumin Fixa- tive,” 115 Mazda light, 82 Media, aberration caused by different, 44 Median line, 81 Medicine dropper, 101 Metals, 206 microscopic examination of, 206 study of, 15 Metals—Continued structure of, 193 what they are, 190 Metamorphosis, meaning of, 168 Metazoa, 138 multi-celled animals, 142 Micropolariscope, what it is, 199 Microscope, 1 a diatom under the, 125 as a legal aid, 13 buying a, 49 care of the various parts of, 74 caring for the stage, 74 choosing place to work, 69 cleaning an objective, 66 cleaning optical parts, 66 cleaning the ocular, 68 coarse adjustment, care of, 75 collecting outfit, 95 attachments, 96 bamboo pole, 96 collecting case, 99 magnifier, 96 two glass bottles, 97 compound. See “Com- pound Microscope” correct way to use, 70 description of, 1 difference between a mag- nifier and a, 3 dissecting to use under, 106 educational uses of a, 9 examination of household articles under, 207 INDEX 241 Microscope—C ontinued examination of metals un- der, 206 fine adjustment, care of, 75 focusing up and down, 72, 73 getting light on your work, 70 getting ready for work, 63 hair of beetle under the, 165 highest forms of animal specimens under, 169 home uses of the, 8 how compound micro- scope works, 33 how it forms an image, 41 how to clean condenser and mirror, 69 how to examine living specimens, 101 how to focus, 72 how to put objective back, 65 how to put ocular back, 66 in ehemistry, 14 in health and disease, 12 in study of metals and minerals, 15 invention of the, 1 kinds of, 7, 8 lowest forms of animal specimens under, 138 mounting. See “Mounts” and “Mounting” Microscope—C ontinu ed nose piece, care of, 77 plant specimens under the, 120 right way to use, 63 sectioning an object for use under, 109 sub-stage, cleaning, 76 taking care of the spoils, 100 taking out the objective, 64 taking out the ocular, 65 technical use of, 12 the compound, 2 the dissecting, 107 the kind you want, 3 using the, 7 what you can see with, 6 See also “Compound mi- croscope” Microscopic objects. See “Objects, Micro- scopic” Microtome sections knife, 107 Milk, 174 Millepeds, 161 Minerals, 191 action of polarized light on, 201 structure of, 193 study of, 15 Minor, 51, 53 Mirror, cleaning the, 69 Mites, 160 Mollusca, 154 structure of, 155 Monsymmetric system, 206 242 INDEX Moss, 129 structure of, 130 the phylum of, 129 Mother-of-pearl, 155 Mounting, 106 how to mount objects, 111 kinds of, 111 Mounts, 44, 105 air, 113 balsam, 116 glycerine, 115 kinds of, 111 permanent, 111 temporary, 111 Mucor mucedo, 127 Multi-celled animal, 142 Musei, 129 Muscles, 183 Mushroom family, the, 129 Myriapoda, 159, 161 Natural light, and substage condenser, 83 Nemathelminthes, 148, 150 Neornithes, 172 Nerves, 184 Nicol prism, use of, 198 Nitrogen, 128 Non-metals, what they are, 190 Nose piece, 59 care of, 77 made parfocal, 59 Nucleus, 121 Numerical aperature, 48 Oblique light, 79 how obtained, 89 use of, 88 Objective, 51, 58 cleaning an, 67 how to put back, 65 how to take out the, 64 immersion, 46 principle of immersion, 47 Objective lens, 39 Objects, microscopic, 92 animate, 92 examining, in the dry state, 103 how to collect, 92 how to illuminate, without a condenser, 80 how to measure magnifi- cation of an, 230 how to photograph micro- scopic, 232 how to section, 109 inanimate, 92 kind of, 78 lighting of, 78 two ways in which light can be thrown on, 91 Ocular, the, 39, 51, 61 cleaning the, 68 how to put back, 66 taking out the, 65 Ocular diaphragm, 68 Oil immersion objective, 58 Opaque objects, 78 how to illuminate, 90 Optical parts, cleaning, 66 Outfit, collecting, 95 Ovipositor, 167 Oxides, 191 Oxygen, 122 INDEX 243 Palmoglaea, cell division in, 122 Paper, 213 Parasites, 126 under a low power, 222 Pedical, the, 131 Penetration, 85 Pericup, 132 Permanent mounts, 111 Petals, 136 Phosphates, 192 Photographing microscopic objects, 232 outfit for, 233 Phylum, 94 Pigment cells, 158 Pillar, the, 50, 52 Pine tree family, the, 131 Pinion adjustment, 56 Pipette, 101 Pisces, 170 Pistil, 136 Planes, 85 Plants, examination of, 10 flowering, 132 of the fungus group, 125 Platy helminthis, 148 Pod, 132 Polariscope, 202 analyzing crystals with, 202 what it is, 197 Polarization of light, 197 Pollen, 136 Polyps, 144 Porifera, 142 Porpoises, 174 Potato starch, 216 Preservatives, 221 use of, 222 Prismatic cells, 155 Prism, refracts fight, 23 Prisms, neutralize disper- sion, 36 Prothallus, the, 131 Protozoa, 138 unicelled animal, 138 Pseudopodia, 139 Pterygota, 163 Pupa, 168 Rack adjustment, 56 Radial symmetry, 148 Reading glass, the, 5 Red corpuscles, 185 Refracting angle, 35 Refraction, index of, 47 Regular system, 194, 205 Reptilia, 172 Resolving power of an ob- jective, 84 Retting, 208 Rhizoids, 129 Rhizopoda, 139 Rhombic system, 196, 205 Rocks, 191 structure of, 193 Rodentia, 175 Roots, 134 Round worms, 150 Salamanders, 171 Saprophytes, 126 Scales, 181 Scalpel, 107 Scissors, 106 244 INDEX Sclerogen, 133 Scorpions, 160 Scyphozoa, 144, 145 Sea Anemones, 146 Seaslug, 157 Sea urchins, 146 Section knife, 107 Seeds, structure of the, 136 Setal, 130 Sharpness, depth of, 85 Shellac, 113 Shellfish, 154 Shifting effect, produced by a cover glass, 44 Shrimps, 160 Sight, the eye the organ of, 18 Silex, 124 Silica, 124 Silicates, 192 Silicon dioxid, 124 Silk, 211 artificial, 212 Silkworm, 211 Single-celled animals, 139 Skin, 182 Slugs, 156 Snails, 156 Snakes, 172 Specimens examining living, 101 how to dissect, 108 lowest forms of animal, 138 Spherical aberration, how caused, 30 how corrected, 33 what it means, 30 Spiders, 160 Spirogyra, 124 Spoils, caring for the, 100 Sponge, structure of, 143 Sporangia, 130 Sporozoa, 141 Springtails, 163 Square purmatic system®, 195, 205 Squid, 158 Stage, caring for the, 74 Stage, the, 51, 55 Staining, 116, 117 Stamen, 136 Starch, 122 Starches, 215 Starfish, 146 Stem, 134 Stomata, 135 Straw fibers, 213 Substage, condenser, the, 51, 53, and natural light, 83 cleaning, 76 Sugar, 221 Sulphates, 193 Sulphides, 191 Symphyla, 161 Tapioca starch, 218 Tasmanian wolf, 174 Teeth, structure of, 178, 180 Temporary mounts, 111 Thousand-legged worms, 161 Thysanura, 163 Ticks, 160 Tissues, 132, 177 Toads, 171 Tools, dissecting, 106 Transparent objects, 78 how illuminated, 79 INDEX 245 Tripod magnifier, the, 5 Tungsten filament lamps, 71 Turbellarea, 148 a longitudinal section of the class, 150 Turntable, how to make, 114 Turtles, 172 Ungulata, 174 Vermes, 148 Vertebrata, the, 169 classes of, 170 Water, 122 examination of drinking, 223 Welsbach gas mantle light, 71 Whales, 174 Wheat starch, 216 Whelk, 156 White corpuscles, 186 Wingless insects, 163 Wings, of the seed, 137 Wood fibers, 213 Worms, 148 Xylol, 67 Yeast, 128 Zoology, 92 division of, 94 Zoophytes, 144 Zygospores, 123 By A. 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