A CORRELATION THEORY 
OF 
COLOR PERCEPTION. 
BY 
CHARLES A. OLIVER, A. M., M. D., 
ONK OF THE OPHTHALMIC AND AURAL SURGEONS TO ST. MARY’S HOSPITAL, PHILADELPHIA. 
REPRINTED FROM 
THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES, 
January, 1885. 1885.] 
Duiiking, Dermatitis Herpetiformis. 
lesions. The flexor surfaces are especially invaded. Upon the thighs 
and legs there is not a square inch that is not the seat of disease. The 
skin which is not occupied by distinct lesions is dark red and violaceous in 
color. The ankles are literally encircled with blebs and pustules, many 
of which have run together forming large, elongate, flaccid, partly bloody, 
dependent blebs. There is everywhere a tendency for the lesions to 
group, and while owing to their great multitude this is not striking in all 
regions, it is nevertheless very manifest in certain localities, as on the 
buttocks and thighs. The groups are for the most part small, consisting 
of from three to five lesions situated within a radius of an inch. In other 
places a dozen or more lesions occupy an area the size of the palm of the 
hand. 
A peculiarity of the lesions is their disposition to coalesce. Inclining 
to manifest themselves in ill-defined clusters of two, three or more, as 
they increase in size they run together, forming larger lesions. Around 
the immediate circumference of these lesions, whether vesicular or pustu- 
lar, smaller, flat pustules or vesicles, the size of pin-heads, are in many 
instances present. When ruptured the lesions crust over with flat, light, 
yellowish crusts. Removing these, superficially excoriated, moist, reddish 
surfaces, having sharply defined irregular vesicular or pustular borders are 
exposed to view. Everywhere about the older lesions there is noted a 
disposition on the part of the process to extend itself in a creeping manner 
while healing in the centre. Itching is present, and is very distressing. 
Dec. 19. A month has elapsed since the last note. During this period four 
distinct attacks or crops of eruption have manifested themselves. The 
lesions in the first three attacks were of the same character as those in 
the outbreak of November 22d, just described at length, namely, vesicles, 
blebs and pustules, with but little inclination to intermediate forms, while 
in the present eruption vesico-pustules predominate. The last two attacks 
have been milder, with smaller lesions, but accompanied with more itching. 
The general course of the disease, the disposition of the lesions to clus- 
ter, and the regions invaded, have been the same as on previous occasions. 
At present the eruption is characterized by many small, and some large, 
variously shaped, vesicles, vesico-pustules and pustules, occurring in patches 
or scattered over the surface, in all stages of evolution, together with 
numerous excoriations, ruptured or torn lesions, crusts and scales seated 
upon a dark-red, violaceous, mottled, pigmented skin, the remains of former 
attacks. The patient is able to be about the house ; his general health is 
good. He has used lately alkaline tarry lotions. Arsenious acid, in doses 
of one-fortieth of a grain, has also been taken for the last three weeks; 
also quinia, and a general tonic treatment. 
In December, 1882 (four years after the last note), I received a note 
from the patient, stating “ I am still troubled with the disease, and it has 
not failed to put in an appearance at certain periods since you saw me in 
1878, although the blisters and pustules have gradually become less, both 
in number and in size. At certain times since, within the year, I was so 
free of eruption that at one time I thought surely I was rid of my pest. 
I can always tell two or three days before the eruption will appear by the 
coming on of an itching sensation. During the past six months I have 
had two attacks.” 
The history of this case, including the cause of the disease—a violent 
shock to the nervous system, is both interesting and instructive. The 
No. CLXXVII Jan. 1885. 98 
Oliver, A Correlation Theory of Color-perception. 
[Jan- 
bullous variety predominated, and when I first saw him, it was highly 
developed; subsequently, however (as in almost every case that I have 
encountered), other lesions, especially pustules, manifested themselves. 
The constitutional symptoms accompanying one exacerbation were 
marked. 
Article YIII. 
A Correlation Theory of Color-perception.1 By Charles A. Oliver, 
A.M., M.D., one of the Ophthalmic and Aural Surgeons to St. Mary’s Hos- 
pital, Philadelphia. 
For some time past the author’s attention has been directed towards 
the many opposing theories of color-perception, some so 
filled with falsities and absurdities as to render them ridiculous, and others 
so veiled with useless perplexities as to maim and alter their intended 
significance. Whilst he is fully cognizant of the fact that he is but add- 
ing to the already overfilled list, he does not hope for indulgence if he be 
in error, nor does he apologize for anything that he may say. Individual 
firm convictions are presented in the knowledge that the only way for 
theory to become a law, is, that each shall contribute his mite of truth 
even though it be buried in a mass of rubbish. Taking for granted that 
the Iluygenian or undulatory hypothesis of the imponderables is accepted, 
and that a difference in the number of vibrations makes a change in natural 
result, it must be self-evident that there can be given three positive asser- 
tions. First. That, as these actions are perceived, there must be organs 
able to appreciate them. Second. That each series of organs must have 
an apparatus able to respond to the quality of its perceived impression. 
Third. That as all natural imponderable stimuli are the resultants of a 
mere difference in the number of vibrations of one and the same ether, the 
organs for the receipt of the different varieties must be but analogues and 
modifications of each other. 
Starting with the idea that each sensory organ is so adapted as to be 
able to receive its variety of impression, the assertion that there is a cor- 
relation in structure and action is arrived at.2 This cannot be denied. 
Take the lowest sensation of animation, touch, and endeavor to compare 
it with the highest, sight. The tactile sense is seen in simplest proto- 
plasmic mass, and it alone enables this primary form of living mechanism 
to exist. There has been given a quality to receive one of the simplest 
1 This theory was brought forward in a preliminary note published in the Phila- 
delphia Medical Times for June 28, 1884. The present writing is the discussion of the 
subject in extenso. 
2 It is not necessary to discuss the first two assertions. 1885.] 
Oliver, A Correlation Theory of Color-perce 
99 
impressions of natural force, an actual contact with a resultant action.” 
What is the visual sense in man, the highest creation, but a complex mass 
of simple elements, an engine capable of receiving many more impressions 
from the imponderables. What is vision but the result of an exalted 
character of contact1 upon a physical difference so arranged as to be 
adjusted to the receipt of undulations equivalent to those of light! The 
physical tactile apparatus does not differ in any way from the physical 
color apparatus except in its form ; the latter a more highly constructed 
variety of the former, each being adapted for its kind of stimulus. Of 
course every grade of animal life has its percentage of sensory power 
dependent upon the special development of the individual. The rate of 
increase being not only in the number of senses, but also in the evolution 
of an individual form. This is well exemplified by the sharp sight of 
some birds, the quickness of hearing, and the keeness of smell of some 
animals. 
There cannot be any doubt of the fact that the special sensory portion 
of the organ of sight is intended wholly and solely for the determination 
of color. The thought that the sense of light constitutes the only visual 
factor of many of the lower grades of animal life, and that it must have 
been the primary form in the evolution of the now existent human visual 
sense, is, strictly speaking, incorrect. Natural colors are the exponents 
of a series of undulations of waves of light existing between two deter- 
minate ratios. Colorless light is the complete synthesis of such color 
vibrations. The more numerous the color combinations, the purer the 
light; the purer the light, the less colored it is; the less colored, the less 
visible. Pure light is invisible. Light to be seen must be colored, it 
must be impure. Consequently visual perception is of color and not of 
light, of which color there may be thousands of intensities of a single 
character of vibration from a dull reflection of a given natural red to the 
most intense reflection of the same natural red. All visual apparatuses, 
from the very simplest to the most complex, receive impressions of vary- 
ing intensities of color. The simplest form of visual apparatus has pro- 
bably but a few differentiations of impure light under its command. 
Thus in the epidermal eye spots of the most rudimentary types of animal 
existence, where resident nerve energies have been lifted from the sensa- 
tion of varieties of heat vibrations into varieties of light vibrations, the 
impressions are limited to a few of the varying intensities of impure, 
colored solar beams. As the scale of life force is ascended, the numbers 
of received impressions increase, dependent not only upon acquired powers 
during the life of the animal, but upon the direct result of hereditary 
transmission of more highly developed physical structures capable of finer 
and more complex action. This continues in an interchangeable and 
1 The so-called “ indirect.” 100 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
irregular ascent until the acme is probably reached in some of the car- 
nivorous types of tropical birds. 
When the human visual apparatus is first placed in the world, and is 
exposed to color waves, it has nerve structures and material, which 
although never having seen the component colors of impure light, are 
physically fitted to respond to many of its vibrations, just as the leg, 
though never having acted, has its definite parts, such as the supporting 
bones, the propelling muscles, the governing nerves, and the supplying 
vessels, each in readiness for immediate action. The first moment that a 
beam of colored light is focused upon a sentient point of an infant’s organ 
of sight, there is a transformation of the impinged natural stimulus into 
an equivalent nerve-energy which is transmitted to a cell, or plants a new 
cell in that infant’s cerebral cortex, thus giving the receiving, transmit- 
ting, and recording cells each a new quality. A second impression is 
similarly received, a third, and a fourth, each stamping the working 
machinery with its representative mark. Repetition upon repetition of 
this occurs in all of the available responsive nerve materials, each single 
cell adding its mite, each mite strengthening and giving greater power to 
the organism, and each organism capable of perceiving as many colors as 
it holds under its jurisdiction. Assuming that complete external synthesis 
of natural color results in colorless light, and that incomplete combination 
in impure or colored light (the impure light being divided into invisible 
and visible), it must be concluded that the value of the total nerve force 
belonging to the various parts of one sensory filament is equal to a quo- 
tient represented by the sum total of all of its individual sensations if 
they had been extraneously combined to form some multiple color. From 
the theorems of natural color which follow, it will be seen that this quo- 
tient of value must be equal to some impure or pure white, but whilst this 
is undoubtedly so, yet in order to avoid confusion, the value of each fila- 
ment’s resident power and related perceptive nerve-force will be ordinarily 
designated as its normal power—merely using the specific terms when 
necessary. In these statements form, magnitude, distance, etc., are totally 
disregarded, because they are the results of combined action, muscular 
changes in and on the eye, changes in intensity of natural vibration, other 
sensory impressions both previously and simultaneously associated, memory, 
intelligence, etc. These taken in measure, or in all, in conjunction with 
the knowledge acquired by the sensory portion of the organ of sight, con- 
stitute what is called sight, the acme of visual result. To briefly illustrate, 
take the illusory effect of a picture representing an every-day scene. Here 
by the careful disposition of color and color only, the artist is enabled to 
seemingly designate form, magnitude, distance, etc., in fact all of the 
factors of sight. In this instance it must be acknowledged that the 
sensory portion of the organ of sight is excited by color vibrations alone, 
yet it is said that by this excitement the mind is brought to believe that 1885.] 
Oliver, A Correlation Theory of Color-perception. 
101 
actual form, actual magnitude, and distance are in existence. How much 
more so for photographs where there are nothing but the so-called black- 
white intensities to act as stimuli ! A moment’s reflection will show how 
faulty the assertion. The mind through the aid of the senses associates 
previous knowledge with the present color perception, which gives rise to 
a pseudo-reality, and the picture appears real. Place the organ of sight 
in an unaccustomed situation where previous knowledge cannot be of any 
value. Allow it to gaze on a picture representing the same subject as 
before, though now seen vertically over the side of a balloon, and it will 
be found to be at an utter loss to correctly recognize anything but color; 
no definite ideas of form, magnitude, distance, etc., can be given. There 
is no previous knowledge, and sight is imperfect. How difficult are the 
attempts to estimate the length of time occupied during the falling of a small 
slip of white paper from a high tower to an uniform green sward ! How 
often the calculation that the object has reached the ground is incorrect! 
The organ of sight is placed in a new and a novel situation, where it has 
no previous knowledge to associate with its present color perception, and 
as a consequence, sight is imperfect and the calculation false. Let it 
assume the same position, say several hundred times, and there will be 
found to be the most accurate idea of both the time of falling and the 
correct distance for that place. There is now previous knowledge to asso- 
ciate with the color perception, and sight for that situation becomes more 
nearly perfect. Crude and vague ideas of magnitude and distance are 
always given by the inexperienced to lone vessels on open seas or solitary 
mountains in deserts. In each case the eye sees as much and as well as 
it ever did, yet sight is imperfect, there being nothing for accurate com- 
parison either in the past or in the present. The sensory portion of the 
organ is alone properly answered, and color perception is the only correct 
result.1 
In telegraphy it is not necessary to possess an uncorrelative difference 
in the form of apparatus to be acted upon by an artificial division of a 
certain alphabet. As the resultants are only modifications of each other, 
they necessitate but corresponding changes in the working machinery. If 
there is a wish to attempt a higher grade of a similar stimulus, the appa- 
ratus is so modified as to allow the record to be correctly produced. The 
tactile apparatus is one form of telegraphic machinery destined to receive 
1 It may be of importance to note that there has been a distinction made in the 
terms “visual apparatus” and “ organ of sight.” This has been intentional. By 
“ visual apparatus” is meant the peripheral and the central sensory nerve expansions, 
with the connecting sensory nerve-fibres, i. e., the ocular or receiving retina, the cere- 
bral or discharging retina, and the connecting sensory fibre (so named optic nerve) ; 
whereas, by “ organ of sight” is designated the visual apparatus in combination with 
the entire ocular appendages—the muscles, the media, the tunics, etc. These dis- 
tinctions apply as well to the other special senses. 102 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
its impressions, whilst the visual apparatus is another form of the same 
machinery intended for the receipt of the same character of impressions ; 
each in itself a simple mechanism, not possessing differentiating power, 
but merely capable of response when properly acted upon. It would be 
foolish to assert that there may be special divisions of peripheral tactile 
nerves especially adapted for the three empirical sensory impressions— 
cold, warm, and hot; then to make an artificial gross division of caloric 
into several arbitrary parts, and say that the different varieties of results 
are the productions of differences in grade and amount of action upon each 
or all of these fibres (that the actions of natural fixed stimuli cause addi- 
tions and subtractions of action in unknown degrees upon organisms of 
elective power). Yet here is Young’s theory applied to the sense of 
touch. A theory slightly modified by such great minds as Maxwell and 
Helmholtz; accepted and held almost without question. Or how ridicu- 
lous to say that there are three tactile substances acted upon and produc- 
ing three-paired primary tactile sensations, each peforming its duty in a 
sort of give-and-take manner, yet at an utter loss of reasoning to tell 
which gives and which takes. Here is the wonderfully ingenious theory 
of Hering considered from a tactile point of view. A theory framed and 
thrown to the world on account of the want of explanation of complemen- 
tary color: a theory blindly followed by this great man’s satellites and 
advocates.1 The same line of criticism might be extended to the senses 
of smell and hearing, in first supposing several arbitrary odor names, or 
taking the now existent musical octave, and then endeavoring to form 
odor and sound theories to explain why these gross recognized differences 
in natural stimuli are smelt and heard.2 
Why take the trouble to give a series of organic elements a coarse un- 
natural division of fibre, in an effort to harmonize them with an arbitrary 
and unscientific naming of visible color, when we have the difference of 
1 As these two theories are the best known amongst those that have been advanced 
since the remotest antiquity, the analogy has been limited to them. 
2 In the arrangement of this argument it might have been better to have compared 
these theories with similar imaginative theorems for musical sensation and perception, 
because not only of the close relationship existing between the two senses employed, 
but of the author’s belief that the special sentient parts of the organ of hearing are 
intended for the reception and transmission of nerve energies equivalent to sensations 
of sound vibration alone, and that our ideas of distance of sound, direction of sound, 
character of sound, etc. etc., are but the results of combined perceptions and concep- 
tions. Nevertheless, he has preferred the use of the sense of touch not only by reason 
of its wide remove in point of evolution from that of sight, but that he thinks the cor- 
relation can be traced here just as well. He also maintains that the peripheral parts 
of the tactile apparatus are destined for sensations of degrees in temperature only, 
which are transmitted as nerve-energies of specific and relative value to be perceived 
by the central organs. Ideas of solidity, weight, etc. etc., are but the results of pre- 
viously gained knowledge and associated impressions from the other senses, combined 
with the so-called “muscular sense,” which is nothing more nor less than an exact 
counterpart of the governing muscles of the organs of sight and hearing. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
103 
result dependent upon a difference in cause acting upon an ever-ready 
material P A difference in the character of natural impression affecting 
one and the same organic element to a greater or less degree, producing 
an exact and equivalent answer. For instance, suppose that a quantity 
of optic-nerve points in the human retina should be exposed to a beam 
of light of undulations, say, equal to five hundred trillions per second, 
the average response to the sensation thus produced upon healthy tissue 
would be what is known as “ red.” Each impinged point would excite 
a sensation equal to a specific energy equivalent to red. Again, suppose 
these same points were exposed to another beam of light of, say, six hun- 
dred trillions of undulations to the second, they would cause a sensation 
which would produce a specific energy giving the response of “green.” 
Or let a beam of light, say of seven hundred and thirty-three trillions of 
vibrations to the second, be thrown upon the same sentient points, there 
would be “violet” given as the answer. Each and every optic-nerve 
fibre tip has a receiving power equal to its individual strength. Each and 
every healthy optic-nerve filament transmits to the color centre for recog- 
nition nerve energies equal to as many special sensations as its peripheral 
tip is capable of receiving. The innumerable quantities of nerve filaments 
placed side by side on a sheet or membrane serves to give greater field, 
and to allow many colors to be seen at one and the same time, thus making 
our every-day and momentary pictures. Therefore, in the author’s opinion, 
the most rational theory is, that color-perception takes place through each 
and every optic-nerve filament. It consists in the passive separation of a 
specifie nerve energy equal to the exposed natural color, from a supposed 
“energy-equivalent” resident in the peripheral nerve tip, by an active 
chemico-vital process of the impinging natural color vibration upon the 
sensitized nerve terminal. The separated nerve energy is transmitted to 
the central terminus of the filament in the cerebral retina, where it is 
fully evolved into such a condition as to be transferred into an automatic 
form of perception by an action upon some unknown contiguous perceptive 
nerve elements: this constitutes the consummation of the nerve energy 
force into the lowest (and evanescent) form of recognizable color-percep- 
tion. Finally, it is carried through similar posts and stations, though 
now of a higher value, as it was whilst pursuing its course inwards as a 
sensation, until at last it is completely recognized as intelligent color-per- 
ception in the higher color centres; these higher color cells being per- 
manent in type, and forming parts and parcels of the higher perceptive 
cerebral centres. The first moment that the primary portion of this action 
(*. e., the separation) has taken place, there has been left in the peripheral 
tip of the primarily impinged sensory filament a nerve-energy material 
equal to the difference between that individual nerve’s “ energy-equiva- 
lent ” and the transmitted nerve stimulus. The healthy peripheral nerve 
tip returns to its “ energy-equivalent,” or normal nerve power, the mo- 104 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
merit the specific energy separated by the received natural vibration has 
been forwarded for transmission and recognition ; whilst the transmitting 
filament and excited cerebral expansion regain their normal condition the 
moment the energy has passed them. After the consummation of such 
an action, the filament is again ready for any other natural color-vibration. 
The whole secret of the theory rests in the fact, that all natural color 
stimuli cause definite losses of nerve-energy material, whilst rest of the 
nerve produces restitution of nerve-energy substance.1 To see red, the 
nerve is first supposed to be charged to its normal physiological condition 
by its inherent vitality and sensitizing material. Vibrations of five hun- 
dred trillions per second—a natural red color—are allowed to be thrown 
upon this sensitized tip. To see the color, the peripheral negative (an 
unused energy equal to the commencing sensation of a green) must be 
allowed to rest, by the separation of a quantity of nerve-force equal to a 
supposed red-energy from the “ energy-equivalent,” through the excitation 
of the impinging ray. This separated specific energy is transmitted to 
the lower color centre, where, although perceived, it is still more fully 
formed into a condition fit to be put upon record by certain higher percep- 
tive elements, thus constituting the highest or intelligent perception ot 
red. The moment that the red energy has left the nerve-tip, the terminal 
is again charged to its energy-equivalent, and is ready to receive any other 
color-vibration that may be cast upon its surface. The same tip is able 
to receive as many impressions of natural color as it holds similar sensa- 
tions under its jurisdiction. Each and every natural color causes the 
separation of a specific energy equal to itself, which is properly transmitted 
and correctly perceived, if the conducting and central nerve structures be 
normal and intact. 
It will be noticed that it is presumed that the sensation must begin in 
the peripheral termination of the visual apparatus (the ocular retina), be- 
cause it is here that the primary change of an external natural force into 
an equivalent nerve-energy takes place, i. e., the conversion of a natural 
impression into the first form of a sensation. This primary form of sen- 
sation is conducted inwardly by the so-termed “optic-nerve” (truly speak- 
ing, the intermediate connecting link of the optic-nerve), and spread as 
more thoroughly adapted and as a finished sensation, upon the intracranial 
retina, in such a form as to be readily converted into an equivalent per- 
ception by the aid of some unknown process of mentality. The sensation 
is first formed peripherally by the impinging natural impression upon an 
individual nerve tip ; it is conveyed inwardly as such, by an intermediate 
1 This is the usual and normal order of progression in the evolution of a recognized 
color-perception from a natural color-stimulus ; although, as will be explained, forces 
can originate in other ways, which may act upon any part of the visual apparatus or 
its related perceptive tracts and cells, and thus give rise to visible results. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
105 
connecting optic-nerve fibre, and at last is evolved upon a definite portion 
of the intracranial sheet or membrane as the same sensation, though now 
completely finished for conversion into a perception of an equivalent 
value : in other words, an impression of natural force upon a special sense 
apparatus, causes a peripheral change of that natural force into a nerve- 
energy (the primary form of the sensation), which is forwarded to a posi- 
tion and in such a manner that it is converted into a perception in certain 
definitive perceptive structures. This reasoning is dissimilar in measure 
from that which would be employed in the usual significations of the 
terms “ sensation,” “ perception,” and “impression,” although in no way 
does it allow the visual apparatus to act as a differentiating body. In 
these remarks, the following distinctions between the terms “ impression,” 
“ sensation,” and “ perception,” have been ventured, which differ some- 
what from those found in the ordinary books bearing upon the subject.1 
1. An impression. The impinging of an extraneous natural force upon 
the peripheral termination of any sensory apparatus. The action of an 
outer world and a receiving material. 
2. A sensation. The action of a sensory nerve. This in all instances 
commences peripherally, where a natural impression is converted into a 
nerve-energy of a relatively equal power; which energy is conveyed to a 
position and evolved into a condition by the transmitting and central struc- 
tures of the apparatus, so as to allow a recognition by contiguous percep- 
tive elements. The work of a receiving, conducting, and discharging 
material. 
3. A perception. The recognition of a properly evolved sensation by 
an act of mentality through the excitation of definite perceptive structures 
in the cerebral cortex connected in some way with the central terminals 
of a sensory apparatus. The action of an inner world and a discharging 
material. 
There cannot be any doubt but that the mind must act in color percep- 
tion, or there would not be any visible world. To perceive color, the 
mentality must take cognizance of the action of an impinging color-sen- 
sation which has been ever altering and becoming higher and higher in its 
physical and physiological growths, from the time it was first formed from 
a peripheral impression of natural color-stimulus. If it be agreed that 
the laws of an act of color perception are similar to those of color-sensa- 
tion, although the character of the labor of the former is of a higher order, 
it must be conceded that physical posts and stations intended for the evo- 
lution of the material qualities of the perceptive agency must exist. 
This implies that as color-perception has its regular development and 
growth, it must necessarily have a scale of efficiency or ratios of percep- 
1 In these definitions, abnormal and pathological stimuli are excluded. 106 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
tive powers. Endeavors to accurately place or express these powers, 
or even to give analyses of their various strengths, are futile as long as 
the union between mind and body remains a locked secret. It may 
be assumed, however, that there is much difference between what 
may be termed intelligent color-perception and automatic color-perception; 
and at this point, at this gross dissimilarity, the human mind with its 
present knowledge is compelled to stop. Automatic color-perception (by 
some termed color-sensation) is the primitive form of the perception, 
where although the color is recognized, yet the mentality is of such a low 
order that the perceptive color cells which have been primarily impinged 
—perceptive cells of evanescent power—would quickly lose their new 
quality, and the color-perception be forever lost, if they had not the power 
of transmitting it to the higher color-cells in the centres where intelligence, 
etc., the creations of the higher mentality, are brought into play, and 
which {dace it, as it were, upon record, so that it may be used in future 
requirements. In this higher situation the perception is stamped, the 
internal consummation of the external force takes place; here it is that 
the higher color-cell is either deposited or augmented so as to be brought 
into action as often as a proper stimulus attacks it; and it is at this place 
that these very cells live and play their roles, growing fat and healthy 
from use, shrivelling and dying from inactivity. What may be the situa- 
tion of these higher cells of permanent powers, and how they live, must 
remain unanswered ; for although physiological experiment and pathology 
have taught the probability of position of the lower forms, they have thus 
far failed to reveal the phenomena of individual and separate existence. 
No matter whether a force be of external or internal origin, if it either 
acts upon these higher-formed cells or makes a new corpuscle, it will 
cause intelligent color-perception (the so-called “perception”), because 
the newly formed higher cell or the increased material is in a proper con- 
dition and a correct situation to act in its turn upon the whole force of 
contiguous mentality. As the greater part of this mentality has been de- 
rived from the accrued results of the other sensory organs as well as from 
the visual apparatus, there may also arise an action of all of the other re- 
sponsive cells, which response will cause an act called sight. So it is 
with the other sensory organs and channels from the outer to the inner 
world. Audition, olfaction, gustation, and taction, each may have added 
to its individual capability such mental factors as will produce hearing, 
smelling, taste, and touch. The manifold combinations of these final re- 
sults with each other as well as with the processes of the deeper though 
derivative mental forces—such as emotion, volition, intelligence—consti- 
tute the ultimata of mental activity. The results of hypnotism, somnam- 
bulism, or in fact any of the so-called disturbances of the ganglion cells of 
the cerebral cortex, conclusively show this distinction. All this bears out 1885.] 
Oliver, A Correlation Theory of Color-perception. 
107 
the saying of Epicharmus, the old Greek poet: “ ’Tis mind alone that 
sees and hears ; all things besides are deaf and blind.”1 
The questions now arise: What is strictly meant by the expression 
“ energy-equivalent” ? Why is it supposed to reside in the peripheral ter- 
mination of each optic-nerve filament? What is its value? What is 
understood by the term “ specific energy” ? Where is its residence ? 
Why.were these nerve-energies chosen ? What is meant by normal con- 
dition ? The combined answers to this series of questions may be given 
in the following paragraphs. At the peripheral tip of every optic nerve 
filament, there must be two separate and distinct actions in the receipt 
and the conversion of a natural color-stimulus into an equivalent nerve- 
energy. First, a separation of a nerve-force physiologically equal to 
the amount of the natural stimulus of the impinging extraneous vibra- 
tion, from the normal conditions of the “ energy-equivalent” resident 
in the tip of the impressed nerve ; and secondly, a return to the now 
lowered remaining nerve-energy material, of an energy matter equal 
to the separated amount of force, the moment the natural color-stim- 
ulus is withdrawn, thus changing the remaining energy to the normal 
energy-equivalent. What this force is, and how it is formed, sepa- 
rated, propagated, and reformed are all difficult problems to attempt 
to answer. Many thoughts, sucli as chemical decomposition, molecular 
vibration or oscillation, direct transmission of vital force, suggest them- 
selves, but no one can positively say which one of these, or whether all, 
or even some other yet unknown force, can be considered as the true sen- 
sory actor, until discriminating instruments can be brought to play upon 
the living and acting organism. It is probably of a purely chemico-vital 
character, placed in such a situation as to permit stimulation of natural 
color upon it. It is not possible to give it any determinate and fixed 
ratio of value, because this must be dependent upon the vitality and 
strengtli of each optic nerve filament. Each tip is born into the world 
and exposed to light with a definite amount of developed physical mate- 
rial just as any hereditary or congenital feature, a foot, a hand, etc., 
and it, through the same amount of physiological action as another optic- 
nerve tip not so well developed, gives greater and finer results than its 
fellow ; thus stamping that individual optic-nerve tip in its peculiar power 
of action. Again, if two tips have primarily the same amount and the 
same grade of physical structure, their life histories may be such, in refer- 
ence to situation, position, exercise, etc., that they will each develop and 
1 The fact that the reader dissents from this division of action in vision, and desires 
rather to believe in the terms “ impression,” “ sensation,” and perception” as gener- 
ally received, does not affect the correctness of the theory at all. The author gives 
but his personal beliefs as to the use of the expressions, which might with equal pro- 
priety be abolished by any disbeliever, and yet the foundation of the fabric remain 
secure and untouched. 108 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
have far different sensory material and power. Roughly speaking, the 
quotient of value of each individual “energy-equivalent” is equal to the 
subjective sensation (with consequent perception) of as pure and as color- 
less an energy as its individual past objective sensations would make if 
they had been extraneously combined as separate color vibrations to form 
a natural impure beam of light (some impure white). 
By the term “ specific-energy” is meant a specific amount of seqsory 
nerve force which has been primarily separated from an energy-equivalent 
resident in the peripheral terminus, by the action of an impression of natu- 
ral color. This separated energy always bears a definite relation to the 
amount of natural color-vibration. After separation, it is evolved into a 
higher grade of action during its passage along the transmitting apparatus, 
until at last, it is spread as an almost fully developed force in a relatively 
similar position upon a cerebral membrane ready to be still further 
charged to a sufficient vitality to act and to be acted upon by some men- 
tal equivalent. 
The reason of the choice of these two forms of this special sensory force 
must be palpable after the above explanations; they serving as full an 
answer to the proposed questions as any other that might be added. 
Besides, such a theoretical designation of nerve-energy admits of much 
more convenient practical testimony in its behalf, than any other form of 
speculative argument bearing upon the subject. 
The last question, “ What is meant by ‘normal condition’ ?” is almost 
self-answerable. It was chosen, however, to serve as an expression of 
difference to the specific term “ energy-equivalent,” as expressing a mere 
physiological rest, just as would be found in the normal condition of any 
other acting body. In this distinction, it must be understood that there 
may be a primary excitation of this material by some internal force, with 
a resultant corresponding physiological action, just as freely as if the 
“ energy-equivalent” had been stimulated. 
This theory has the following theorems of natural color for its basis :—1 
1. The general convenient adoption of the seven so-called primary 
colors, or of the solar spectrum being made of three graduated overlaying 
spectra must be discarded, as these are nothing more nor less than crude 
visual and mental distinctions made through the want of perfect physical 
condition and physiological ability. 
2. A difference in kind of undulation makes a change in natural color, 
and every such change must be called a “ primary natural color” or a 
“pure natural color”; on account of its being the representative of a 
specific character of vibrations totally different and distinct from any 
other primary natural color. There are as many separate primaries or 
1 By “ natural color” is meant every species of independent and combined light 
vibration (except total synthesis), in contradistinction to “visible” or “sensory 
color,” which is a mere visual and mental exponent of such wave lengths. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
109 
pure colors as there are difference in undulations between the extremes of 
color-vibration. 
3. A “secondary natural color” or a “tone” is the result of the addi- 
tion of any two pure natural colors or primaries. 
4. A “ multiple natural color” is the result of the addition of two or 
more tones, or of more than two pure natural colors. 
5. Colorless light is the compound of all natural color, the origin of all 
separated natural color vibrations. The purest example may be repre- 
sented by the synthesis of a resultant spectrum produced from the com- 
bination of all of the spectra of all of the natural elements in all possible 
conditions. To human knowledge, there is no single natural body which 
contain all of the natural elements; consequently to human knowledge, 
there is no individual body that can give rise to pure colorless light. 
Every light-giving source, such as a sun, electricity, chemical and animal 
change, gives a definite color-spectrum equal to its constituent elements. 
Hence there must be two varieties of colorless light, pure and impure.1 
6. By an inherent synthetical power, every light-giving source gathers 
and collects all of its individual elemental spectra into a compound natural 
energy. Portions of this energy are propagated into all free space as un- 
dulations equivalent to those of invisibly impure and visibly impure color- 
less light. These vibrations upon being received by a natural object, are 
either fully absorbed, totally reflected, or broken into two portions, the 
absorbed and the reflected ; this being dependent upon the nature of the 
impinging beam and the character of the impinged object; the reflected 
portion gives the natural color to the object. The amount of the separat- 
ing action is dependent upon the relation existing between the active 
power of the impinging beam and the passive resistance of the body. A 
slightly impure beam is able by its relative action upon innumerable 
bodies to separate itself into innumerable colors, whereas a decidedly im- 
pure beam separates only the varying tints and shades of its own kind.2 
7. Pure complementary color. Every natural color has its complemen- 
tary, to which, if it be combined in certain ways by a natural object, gives 
either pure white or pure black. 
Pure white is caused by the simultaneous reflection in a definite, direc- 
tion of any two pure complementary colors, or of any even multiples of 
pure complementary colors, from an impinged natural object. Hence, 
1 The impure white light of the earth’s sun is an impure colorless beam, the repre- 
sentative of the solar constituents. 
2 As a matter of course, the visual apparatus cannot see invisibly impure light. 
Such light falls upon the sentient parts of the retina as well as upon any other natural 
body which absorbs and reflects. The amount of reflection gives to these sentient 
tips their natural color. They are fitted to respond only to energies equal to imping- 
ing reflected rays. (All transmitted rays to be seen, must have surfaces or points of 
reflection.) 110 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
pure white is a positive or a visible tone, of which there may be innume- 
rable varieties. 
Pure black is caused by the simultaneous absorption of any two pure 
complementary colors or of any even multiple of two pure complementary 
colors, by the passive action of an impinged natural object. Hence, pure 
black may be considered as a negative or an invisible tone, of which there 
may be innumerable varieties. It is not a color, and has darkness for its 
equivalent. 
8. Impure complementary color. Every natural color, primary, 
secondary, or multiple, has innumerable impure complementaries. If 
there should be a combination in certain ways of any one or more of these 
natural colors with one or more of its impure complements, there will re- 
sult an impure white or an impure black—a tint or a shade. 
A tint is the simultaneous reflection in the same direction of two or 
more impure complementary colors, from an impinged natural object. 
The preponderant wave serves as a basis for the color. 
A shade in the simultaneous absorption of two or more impure comple- 
mentary colors by the passive action of an impinged natural object. 
9. Darkness : two conditions. 
a. Produced by the interference of two or more series of undulations. 
The rising phase of the one exactly corresponds in position and time with 
the sinking phase of the other; thus they neutralize each other, and give 
rise to the loss of positive color. It may be designated as positive undula- 
tions so interfering as to give negative results. Of these, there may be 
many varieties. 
b. True absence of light undulation. Here there are no stimuli produc- 
tive of color ether-waves, hence no results, either positive or negative. 
This condition is directly opposed to pure colorless light. 
Physiological Research—As before intimated, in the human sys- 
tem, every special sense apparatus has three separate parts. First, a peri- 
pheral expansion intended for the reception of natural vibration equal to 
its powers of primary sensation. Second, a series of telegraphic com- 
munications, inclosed and insulated, separated and adapted for the trans- 
mission and the partial evolution of equivalent nerve energies. Third, a 
central expansion, upon which is spread the received result, ready to be 
fully evolved and transformed into a perception by a contiguous nerve 
material endowed with the power of mentality. The visual apparatus is 
but one of these forms; a sensory nerve development adapted for impres- 
sions of color; and from this standpoint it must be studied. Naturally, 
inquiry w'ould be made for methods of determining the comparative rela- 
tions existing between the exciting stimuli and the degree of sensory 
power of the apparatus. Mathematically, this has been found totally in- 
adequate ; so that at present, not possessing any absolute data for ratios Olivee, A Correlation Theory of Color-perception. 
1885.] 
111 
of equivalence between the strength of the impinging beam and the ap- 
preciation or value of sensation of the receiving fibre, except those based 
upon physiological investigations and clinical experience, these have been 
deemed sufficient for a time at least, to endeavor a proper enunciation of 
the theory. The question of the value of theorizing as to the modus 
operandi falls to the ground, the moment that it is unbiasedly considered 
that having hut one premise fixed to the equation no conclusion can he 
arrived at. Theoretically, the beam of light of the least number of vibra- 
tions should be that of the easiest recognition, hut then the questions arise— 
Does not such a beam cause less sensory disturbance? Does it not excite 
the filament the least? Would not a stronger natural impression give a 
correspondingly stronger nerve-energy ? What relation may the intensity 
of the natural color vibrations have upon the ease of impression ? All of 
these are serious questions, which must remain unanswered until ingenious 
instruments of such precision are made, that can with unerring accuracy 
and the utmost delicacy give the actual rates of known impression and 
passage of equivalent nerve-energies. All, therefore, that can be reason- 
ably presumed, is, that there must be a normal condition to which the 
nerve filament must return after each individual impression has been con- 
veyed. This has been brought forward more at length in the previous 
part of the paper, and upon it the whole superstructure rests. In this 
section of the subject endeavors shall be made to study and give some 
physiological explanations for its choice, and add a few reasons why its 
probability may be entitled to belief. After much deliberation, it has 
seemed best to consider the different results under the following heads : 
First. Color-perception as produced by color-sensation commenced in 
the macular region of the ocular retina. 
Second. Color-perception as caused by color-sensation primarily formed 
in the circummacular region of the ocular retina. 
Third. Color-perception directly resulting from provoked remaining 
nerve-energies. Subjective after-color (so-called complementary color). 
Fourth. Color-perception caused by the action of internal stimuli upon 
nerve-energies which have not been lowered by any preceding act. Sub- 
jective color. 
First. Color-perception as produced by color-sensation commenced in 
the macular region of the ocular retina. From time to time experiments 
have been instituted in various ways to determine the qualitative and 
quantitative limits of normal color-perception derived from color-sensation 
primarily made at the macula lutea. Those for the determination of the 
latter have been the more numerous, and these have been limited to a few 
of the more important and valuable color differences. As might be ex- 
pected from theory, experimentation has revealed that although all indi- 
vidual macular regions have definite relative powers with each other, yet 
no two possess exactly the same amount of color-sensation ; thus con- 112 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
clusively showing that each lias a different amount of nerve-tissue and 
nerve-energy. This can be understood when it is considered that the 
great varieties of physical differences in similar normal organs, must 
necessarily give proportionate differences in normal physiological action. 
Consequently, here it has involved the use of standards for a proper solu- 
tion of the average strength of color-vibration upon those optic-nerve 
filaments which are deemed by all physiologists to be of the highest 
physical organization—the filaments resident in the yellow-spot. Briefly, 
the order of the standards for five of the most important colors have been 
red, yellow, blue, green, and violet, showing that a natural red vibration 
excites an optic-nerve filament the quickest, followed by the others in the 
order given above.1 At present it will not be necessary to offer any ex- 
planation why these colors follow each other with such regularity. Suffice 
it to say, that, as before intimated, it can never be hoped to gain a proper 
solution to the problem until vital energies can be reduced to mathematical 
certainties, although an adequate answer, based upon the combined results 
of physiological research and pathological study, will be reserved for the 
concluding paper. 
Second. Color-perception as caused by color-sensation primarily formed 
in the circummacular region of the ocular retina. Really no sharp line 
can be drawn between these two headings, as one is a gradual lessening of 
the other ; but as the experiments have been dealing, in the investigation 
pursued in this connection, with the furthermost limits of the generally 
used portion of the ocular retina, in contradistinction to those of direct 
use, it has seemed better to make the classification so as to have a com- 
parison between the weakest and the strongest filaments of the nerve. 
Two plans were adopted: One, to consist in the study of the ordinary 
visual fields, and the other in investigations as to the possible recognition 
1 This has been partially determined, and will, probably, be continued by the writer 
in experiments differing somewhat in detail of method from any others with which he 
is acquainted. An emmetropic eye with good color vision is placed at the extremity 
of a blackened tube six metres in length by ninety millimetres square. No light is 
permitted to enter the eye, except from the opposite end of the tube, and this through 
a graduated double shutter, practically similar in all respects to the author’s color- 
sense measure (description in Archives of Ophthalmology, vol. x. No. 4, p. 438), with 
the exception that transmitted light is used instead of reflected, as in his previous ex- 
periments ; this being accomplished by the substitution of thin, transparent plates of 
colored glass, or gelatine, in the opening between the shutters, for the squares of colored 
paper previously employed. The movable slides in the newly adapted color-sense 
measure are slowly separated, and the area of exposed color registered the moment it 
is properly designated. This plan is pursued in such a manner that there can be 
nothing but a certain amount and kind of color-stimulus to affect any desired region 
of optic-nerve filaments. To complete the experiments, and to make them of fixed 
value, there should be some mechanical device constructed by which the shortest time 
necessary for the perception of the color could be accurately determined and registered. 
Valuable results might also be obtained by diminishing the illumination as in the ex- 
periments of Bull. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
113 
of all of the colors (equal to the power of the individual macula lutea 
region under observation), in the periphery, by increase in illumination or 
in quantity of color exposed.1 As far as gone, all of these showed the 
following results:— 
1 It has not been thought necessary to accurately describe the proposed methods, 
but merely to state the character of experiment with a description of the instruments 
in use. For the first series, perimetric observations are made with areas of reflected 
color upon both black and white surfaces, as well as examinations of the same char- 
acter, by the employment of transmitted color-stimulus alone. This latter method is 
deemed worthy of full description, not that the device of instrument is the best, but 
that the plan in itself is probably the only proper way to obtain accuracy in the size 
and extent of the different visual fields. In a large darkened box with a circular 
opening cut into one of its sides, there is placed a normal emmetropic eye, at about 
thirty centimetres distance from a small roughened woodeu button fastened against 
the upper end of a narrow flat glass rod so arranged that both the eye in the box and 
the button in the centre of the open area will be situated on the level with each other. 
This window is of much greater size than any normal visual field. A piece of paste- 
board several times larger than the opening in the box is held against the window. In 
the centre of this pasteboard screen there is a hole of one centimetre square, in which 
can be placed thin sheets of colored glass or gelatine. As many pieces of color may 
be used as desired. By sliding the large pasteboard card so that its central hole may 
be allowed to perform excursions in all directions from the periphery of the now 
covered window to its centre (which centre is made visible to the eye within the 
darkened chamber by the rubbing of the wooden button with a piece of stick phos- 
phorus), the hole in the immense shutter is caused to act as a definitely sized area of 
movable transmitted color stimulus. The moment the color is recognized, as it is 
brought inwards, its distance from the luminous button is measured, so that when the 
circle is completed, the different distances can be registered upon small memorandum 
slips ruled to proportionate values of space. As many different color fields as desired 
can thus be taken, and small registers kept for future reference and accurate compari- 
son. The objections as to the methods being crude, cumbersome, tiresome to the 
patient and surgeon, the difficulty of working the instrument, etc., might be easily 
overcome by the substitution of adaptations of better construction. In the studies pur- 
sued in this paper, all this would be but afterthoughts, as here it is but desired to get 
a working instrument of sufficient capability to give proper answers to the experi- 
ments. The advantage of the plan must be manifest in the fact that there is no other 
stimulus present except that of the desired color and a faintly luminous spot of just 
sufficient visibility to keep the optic nerve fibres of the macula lutea fixed in a position 
to preserve proper steadiness of the globe. 
The second series of experiments, where it is designed to study the comparative 
strengths of the most peripheral and the central distribution of optic nerve fibres in 
the ocular retina, have been partially attained and will be probably accomplished by 
putting the eye in a darkened chamber. The macula lutea will be kept fixed upon a 
small, white, faintly-luminous object consisting of the passage of common daylight 
through a piece of uncolored translucent glass placed in a hole one millimetre square 
cut in one wall of the chamber. In a position corresponding with the most periphe- 
rally used parts of the retina (i. e., the outer horizontal meridian of the visual field), 
thin, transparent plates of colored glass or gelatine of known values are to be placed 
in an opening ninety millimetres square cut in the wall of the chamber in which the 
central hole is pierced ; this opening can be changed in position to correspond with 
each case. In this opening there i6 a movable slide of the same character as in the 
author’s color-sense measure, by the working of which, any desired amount of color 
surface may be impinged upon by direct and indirect beams of sunlight of greater and 
No. CLXXVII.—Jan. 1885. 114 
Oliver, A Correlation Theory of Color-perception. 
1. By the same amount of daylight, the superposition of a definitely 
sized area of unglazed reflected color upon a dead black surface, gives the 
largest visual field to white, followed by yellow, blue, red, and green in 
the order named. 
2. By the same amount of daylight, the superposition of a definitely 
sized area of unglazed reflected color upon a white surface, gives the 
largest visual field to yellow, followed by blue, red, and green in the order 
named.1 
3. Perimetric observations upon black backgrounds, show that with 
equal illumination, all reflected colors undergo definite changes during 
their passage across the fields towards macular fixation. 
The following is the order for those experimented with: A definite 
area of white first gives a peripheral sensation of gray, which gradually 
passes to white. The same size of yellow impression, first appears as 
gray, then white, then lemon-colored, and at last yellow. Blue first 
appears as gray, and successively passes to white, bluish, and blue. Red 
first shows itself as gray, then white, followed by orange, salmon-color, 
and red. Green first appears as gray, then white (sometimes bluish), and 
then greenish, before it gets to its true color. 
4. In perimetric observations with reflected color upon a white back- 
ground, the same phases of color-change are undergone as in similar ex- 
[Jan. 
greater intensity, at last supplanted by gauged intensities of electric light. These 
beams are made to pass through a blackened tube six metres in length by ninety milli- 
metres square, placed on the outside of the chamber; the extremity of the tube being 
fastened against the large eccentric opening containing the different colored plates. 
This contrivance enables us to expose to the peripheral portion of the observing retina, 
graduated intensities of chosen colors. Notes of the size of the color stimulus and 
of its intensity will be taken as soon as the color is properly called. A ready compari- 
son between the qualities of the same color as perceived through the peripheral fibres 
of the ocular retina and through the macular fibres of the same ocular retina, will be 
made by putting a similarly colored piece of glass or gelatine as has been used in the 
large eccentric opening, in the place of the plain translucent glass used for macular 
fixation, and giving to it the same amount of illumination as has been used for the 
peripheral color. To estimate the proportionate physiological values of the most 
peripheral and the macular optic-nerve filaments, more and more surface of the eccen- 
trically seen area will be exposed until the macular and the peripheral colors are 
determined to be as alike each other as can be gotten. (This plan is but a modifica- 
tion of that of Charpentier. Snellen, Landolt, and Aubert have experimented in other 
ways.) After the establishment of the visual results, valuable information as to the 
order of peripheral loss of colors could be easily gotten in a series of converse experi- 
ments by mathematical diminution of color intensity and area. 
1 As black is not a color, its relative situation was not placed in the list, although a 
similar area of it upon a larger surface of white was tried, which showed a projected 
position of the unimpinged optic-nerve filament into the visual field. This area of 
defect was made known far more peripherally than the places of primary receipt of 
any of the color vibrations, on account of its being inclosed in a space of recognized 
white stimulus. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
115 
periments upon a black background ; every color tried, with the exception 
of white, first appears as an area of non-impression.1 
5. When visual fields are produced in the same amount of daylight, by 
the use of transmitted color, the largest area is that of white, followed 
by yellow, blue, red, and green. 
6. As far as investigations have gone, the following may be laid down 
as a rule. By increased light stimulus all of the different colors responded 
to by optic nerve filaments in an individual macular region can be recog- 
nized when exposed to the most peripherally used elements of the same 
retinal area.2 
Third. Color-perception directly resulting from provoked remaining 
nerve energies. Subjective after color (so-called complementary color). 
The term complementary color has been avoided because it does not 
express the true condition of things; it only shows that there is a color 
which appears to be the complementary of another color previously seen. 
Therefore in consequence of a wish to give a precise designation for the 
character or kind of action as well as one for the state of existence of the 
working material, in the place of a term which is merely indicative of a 
recognizable symptom, the above expression has been substituted. 
Possibly it might have been advisable to have placed this part of the sub- 
ject under the heading of the so-called color-blindness, because both con- 
ditions are nothing more nor less than true species of each other. As will 
be explained, the former is a momentary faulty answer, the resultant of 
imperfect physiological work, through normal physical incapability; 
whilst the latter is a permanent3 faulty answer, the resultant of imper- 
fect physiological work through abnormal physical incapability. On 
account of “ complementary-color” being as universal as vision itself, it 
has assumed a similar physiological basis, and must be considered under 
1 This is readily explained. In this experiment we are dealing with a white back- 
ground, which is the largest visual color-field. All the other color-fields are propor- 
tionately smaller; hence the boundary of the white field must be the peripheral limits 
of color-vision. A small white area is first seen as gray at the border of its white 
field, because at this point it necessarily must give its first weak sensation. The other 
color areas have a certain space of peripheral white color vision to travel over beiore 
they commence to be recognized ; consequently, the superposition of one of these 
natural colors anywheres in this space, must necessarily take away the vision for 
white in the superimposed position, and yet fail to give any impression whatever. 
Hence as a consequence, there is an area of subjective darkness—an area of unrecog- 
nized color-stimulus. 
2 The author’s experiments in this direction have not been completed, They have 
been limited to the mere question of recognition of the five color»differences—white, 
yellow, blue, red, and green. He has partially determined that the comparative 
values of the experimented colors are in the order as given above. 
3 By “permanent” is meant a time corresponding to the continuance of the causa- 
tive pathological structural change. 116 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
the physiological laws of the visual appai'atus.. Hence it has been placed 
here. In order to facilitate the studies in this branch, the results and 
reasonings of previous investigators have been combined with some 
additional experiments and analyses, and from these, certain suppositions 
as to causation have been framed. As said in the other headings, it does 
not seem necessary to give each individual example of research ; for, 
besides being burdensome, it would but add much unnecessary detail, 
where resultant averages could be readily formulated and briefly given. 
It must be granted that all such changes are necessarily of a purely sub- 
jective type—a momentary alteration of physical structure causing a 
consequent relatively faulty answer. The exciting stimulus may be either 
peripheral or central—external or internal ; it does not matter which, as 
long as there is a passing fault in the machinery, there will be a corres- 
ponding fault in the product. This gives the first grand division of 
“ subjective after-color first, those produced from the external world or 
natural light stimulus ; and second, those from some internal stimulus, 
either in the visual apparatus, or in the cerebrum beyond it. In a previous 
paragraph it has been more fully shown and explained that every sensory 
nerve has at its peripheral termination two separate and distinct actions 
in the receipt and the conversion of a natural color-stimulus into an 
equivalent nerve energy; first, a separation of an amount of nerve force 
equal to the amount of an impinging natural stimulus, from the normal 
condition of a resident nerve-energy ; and second, a regain or a return of 
an equivalent amount of material to that nerve’s “ energy-equivalent,” 
the moment the natural stimulus is taken away. This rule holds good for 
the entire length of the sensory filament as well as for the related percep- 
tive elements in the cerebral masses. Should there by any means be 
another color-stimulus presented to the primarily impinged optic-nerve 
filament tip, before it has had time to regain its normal condition, the new 
color-stimulus will be reduced in its equivalent action by as much as the 
primary color-stimulus has taken away, and the result in all cases will be 
a proportionate difference. In other words, there is a moment before the 
lowered sensory nerve can be made to properly obey its physiological law. 
Thus, suppose a red stimulus should be superimposed upon a white stimu- 
lus (t. e., a red wafer upon a sheet of white paper), and that the red 
vibrations should be allowed to impinge upon an optic-nerve filament, 
the natural stimulus would separate a nerve-energy equal to itself from 
the “ energy-equivalent” of the impinged optic-nerve filament, and con- 
tinue to do so as long as the red stimulus is there. This is an act of 
continued separation. Again, suppose that this natural red color should 
be suddenly removed. By this act there would be a natural stimulus of 
white sent to the same nerve in which the “ energy-equivalent” has been 
lowered to an energy of an amount equal to the difference between the 
nerve’s normal power and the red energy. No time has been allowed for Oliver, A Correlation Theory of Color-perception. 
117 
1885.] 
the “ energy-equivalent” tQ be properly re-formed. There would now be 
a dual action for the impinged nerve—a regain of the separated amount of 
the red energy, and a separation for the impression of the natural white 
stimulus. The result would be a difference between the white and the 
red, whieh is equal, in this case, to the commencing sensation of some 
green.1 
The same thing occurs when the so-called complement is provoked 
upon some other color surface than white. By the sudden substitution of 
a new color-stimulus, the excited nerve is rendered momentarily abnormal 
for the amount of regain of the primarily seen stimulus. If this second 
color-stimulus be of greater value than the amount of nerve-energy left in 
the optic-nerve filament tip, the actual result will be an answer to a nerve 
action equal to the amount of energy left by the primary stimulus, which 
of a necessity will always be a complement of the primarily seen color. 
To explain : if a natural red stimulus be superimposed upon an orange 
ground, theoretically in this particular instance, there would be either one 
of two things, each dependent upon the separating power of the second 
color. First, a proper receipt of the natural orange color (in which case 
there would not be any complement at all, because both the primary and 
the secondary natural color-stimulus would be properly answered), pro- 
vided that there be sufficient nerve-energy material left from the separat- 
ing action of the primary red stimulus upon the energy-equivalent of the 
optic-nerve filament tip, to be separated for transmission and perception of 
the after natural orange stimulus. (Here the separating power of the 
second natural stimulus (orange) is considered to be low.) Second, a 
subjective after-color of some green upon the orange ground. The remain- 
ing energy would be stimulated to its utmost by a natural color of greater 
power than it is capable of receiving. As has been shown, the energy 
that is left'is always equal to the subjective complement of the primarily 
seen color ; and, as a consequence, this amount of energy is all that can 
be separated for evolution into a completed perception. (In this latter 
supposition, the separating power of the second natural stimulus (orange) 
is considered to be high.) This latter is what takes place when the 
so-called complement is produced. 
The belief that black is the complement of white is obviously incorrect 
because it is based upon false premises. This refutation admits of ready 
1 A good example of a subjective after-color produced from a natural white light 
after prolonged exposure of the eye to a red stimulus, was once experienced by the 
writer. One dark night whilst he stood watching some men at work before the blast 
furnaces of a large rolling-mill, his attention was particularly attracted towards 
several huge pieces of iron heated to a cherry-red color, that were standing in a dark 
corner. He gazed at the blocks for some time, and upon turning to walk down an 
unlighted street, noticed that the light of a distant lamp appeared bright green, and 
continued so until he had nearly reached it. He then saw that the lamp was covered 
by a white shade. Oliver, A Correlation Theory of Color-perception. 
[Jan. 
118 
explanation ; for when a certain number of optic nerve filament tips have 
been exposed to a definitely sized square of natural white stimulus upon 
a larger area of neutral gray surface, there is an answering nerve material 
separated as a white energy as long as the tips are directed towards the 
natural stimulus. As this white natural stimulus has been derived from 
an ordinary impure natural colorless energy, it contains all of the com- 
plements of that natural energy, and par consequence must have impressed 
and separated all of the nerve material of the impinged tips. This sep- 
arated white nerve energy is transmitted and evolved into a perception of 
white. Suppose this certain natural white stimulus be stopped, and an- 
other similarly sized and placed area of white stimulus be given to the 
impinged nerve-tips before a formative action could have taken place in 
the nerve energy material; all white sensation and perception would be 
at an end, because the second white natural stimulus would take away the 
nerve-energy material as fast as it would endeavor to re-form, and would 
not allow any of it to be separated for transmission and perception. This 
condition would last until the nerve-energy material could sufficiently 
regain itself for separation. Consequently there would be a space of true 
physiological darkness equal in size to the space occupied by the prima- 
rily perceived white color, which was produced from the first natural 
white stimulus: an area of “ physiological nothing” made visible by sur- 
rounding color, just as a hole in a board is seen ; this area being depend- 
ent upon the inability of the peripheral tips of a quantity of sensory nerves 
to properly receive a series of impressing natural waves. This can be 
proved by the following experiment: Make of unglazed paper a card 
containing three concentric rings, each ring of three centimetres width. 
Let the middle one be white, and the two outer ones black. Hang the 
contrivance directly in front of a nine centimetres wide ring of white paper, 
upon the gray wall of a badly-lighted room, in such a manner as to com- 
pletely hide the white-ring card. Gaze attentively at the black and the 
white rings for at least fifteen seconds. (Preferably do this when tired 
and fatigued, as the result is much more prompt and vivid.) Whilst keep- 
ing the eye steadily fixed, have the outer card suddenly removed, which 
action will give the impinged optic nerve filament tips a white stimulus to 
respond to. Instead of a receipt of white there will subjectively appear 
three concentric rings, the outer ones being white, and the inner one 
dark. This experiment also explains the fact that the exposing of sensi- 
tive peripheral nerve-tips to a black surface does not cause a separation 
of sensory nerve force in the exposed terminals; thus conclusively show- 
ing that the popular idea of white being the complement of black, is 
nothing but a crude and false deduction based upon premises which con- 
found a want of action with action—an error that has arisen through the 
belief that a black surface is an area of natural sensitizing material. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
119 
The superposition of a natural white stimulus upon any other natural 
color-stimulus than white, practically causes an area of momentary dark- 
ness, because the primary natural white stimulus has used all of the resident 
nerve force, and time has not been allowed for the formation of sufficient 
material to transform the second natural stimulus into an equivalent 
nerve-energy. This want of action prevents the second natural color from 
being perceived. 
The series of passing subjective after-colors produced by excluding all 
natural light rays from the visual apparatus, after it has gazed for some 
time upon pieces of white paper on black surfaces, held in direct sunlight, 
seem to depend upon the fact that the primary extraneous white stimulus 
has been of such great intensity that even after it has been completely 
removed, it has left an irritant action in the exhausted peripheral tips, 
which of a necessity will separate for transmission and perception specific 
nerve-energies from the re-forming material as last as the material is poured 
into the tips. The fact that the irritant action is ever decreasing, with a 
proportionate gain of the nerve-energy material in the tip, is the cause of 
the succession of subjective colors. For instance, a definite number of 
optic nerve-filament tips have been exposed for some seconds to a white 
stimulus of very great intensity. The extraneous stimulus is suddenly 
stopped. All of the nerve-energy material has been extracted from the 
exposed tips. A formative action immediately takes place, but this is 
met with an irritant in the shape of the remains of the intense white 
natural stimulus. A contest takes place between the formative action of 
the nerve-energy material and the irritant. The irritant separates the 
nerve material as fast as formed. The gradual loss of irritating action is 
evinced in the passing changes of perceived color. The victory is given 
to the nerve-energy material, because the material has had a source of 
constant renewal, whereas the irritant action has died from the want of 
fresh supply of natural stimulus. It may be that this result is indirectly 
augmented by a devitalizing action of the intense white stimulus upon the 
organic constituents of the tip itself, which physicial alteration prevents 
proper physiological working; the various color changes being dependent 
in some measure upon the character of the reparative action taking place 
in the recipient tissues. This supposition is borne out by the so-called 
blending effect of direct sunlight upon the human retina. 
If, instead of excluding the visual apparatus from all natural light after 
it has gazed for some time upon the pieces of white paper on the black 
surfaces held in the bright sunlight, it should be immediately re-exposed 
to the same slips of white paper to which the first exposure was made, 
there will subjectively appear the same character of passing colors as were 
made subjectively visible in the preceding experiment, except that now 
they will progress in a reverse order. The reason for this can be readily 120 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
given. During the time that the reimpressed exhausted tip is gradually 
gaining sufficient nerve-energy to transmit the second natural white stimu- 
lus, there is a corresponding separating process continually taking place, 
dependent upon the great intensity of the second natural white stimulus. 
These separated amounts of nerve-energy are forwarded to the perceptive 
centres where they are recognized. This continues in a definite order of 
gain, until at last the second natural white stimulus is able to be properly 
received as an equivalent nerve-energy, which is transmitted and per- 
ceived as “ white.” 
Both of these experiments first show the so-called “objective comple- 
ment” of the primarily exposed natural color, followed by visible expres- 
sions of regain of nerve-energy material under different circumstances. 
The subjective after-colors seen by an eye exposed to a feeble stimulus 
of natural color when its fellow is made to receive a strong stimulus of 
some other natural color, must necessarily be dependent upon a transfor- 
mation of a “remaining energy” of one of the primarily used perceptive 
color-cells belonging to the strongly impressed visual apparatus, to an 
equivalently placed perceptive color-cell belonging to the weakly impressed 
visual apparatus; the primary weak excitation of the secondarily and in- 
ternally impinged perceptive color-cell causing a primary separation of but 
a minimum amount of nerve-force material to be regenerated for recogni- 
tion and projection of the internal stimulus. It is nothing but the action 
of the “ remaining energy” of a lowered though highly excited perceptive 
color-cell belonging to one channel to the external world upon another 
similar and responsive perceptive color-cell with a “ remaining energy,” 
belonging to a like channel to the outer world. As the most probable 
cause for this character of response must have been dependent upon a con- 
nection of the perceptive cells belonging to the two sensory apparatuses, 
although, from the very nature of things, all normal human cerebral action 
must ordinarily be dual in its physicial nature and physiological action, 
yet it is the most reasonable to suppose that at the time of the double 
action of the visual apparatuses, the perceptive cells of each were physi- 
cally and physiologically thrown into connection with each other. How 
this may have been done, whether by continuity of material tissue, chemico- 
vitally or by some unknown agent, it is impossible to say. That there is 
an organic or life connection at such times is known by the blending of 
the finite results ; but even if continuity of molecule could be traced during 
such action, the fact of a new perceptive color-cell being attacked by a 
definite stimulus, which sets free a specific energy, does not destroy the 
weight of the argument that might be forwarded for not considering it a 
“ subjective after-color” in the same light as the author, because the inter- 
nally impinged cell has been lowered to a “ remaining nerve-energy” by 
its weak primary action. Thus, in one of the interesting and ingenious 1885.] 
Oliver, A Correlation Theory of Color-perception. 
121 
experiments by Gorham,1 where a subjective green is made to appear to a 
visual apparatus which has been exposed to a weak natural white stimulus, 
whilst the opposite visual apparatus has been given a strong stimulus of 
natural red color, the answer cannot be arrived at in any other way. The 
fact of white being the weak primary separation in this experiment appears 
as a vulnerable point in the argument; but the force of this is contro- 
verted by the extreme weakness ot the intensity ot the action from the 
natural white color, in contradistinction to the great strength of the oppo- 
site internal stimulus, the question being one of a difference in intensity. 
The same character of reasoning that has been offered in explanation 
of the preceding class of experiments may he adduced in favor of the so- 
called “ simultaneous contrast colors,” in showing that either the action 
of simultaneously powerful and feeble intensities of natural color stimuli 
or of a prolonged exposure of a strong and a weak natural color impres- 
sion upon a series of contiguous peripheral nerve terminals of the same 
visual apparatus can readily provoke an internal irritant action in the 
strongly excited perceptive color-cell, which will, in its turn, cast the 
entire brunt of its remaining nerve-force upon its feebly excited neighbor, 
and thus rouse the now secondarily impinged cell into a corresponding 
action. This is found to be most likely the case, when it is remem- 
bered that these cells have probably through their simultaneous primary 
action been physically and physiologically thrown into connection with 
each other. It will not be necessary to give the many variations of this 
variety. The recital of two experiments will suffice for all. First, when 
a small square of weak red stimulus placed upon a large area of intense 
natural red appears greenish, the supposition as to causation belongs to 
the first rule—“ simultaneously powerful and feeble intensities.” An 
experiment illustrating the second rule, i. e., prolonged exposure of a 
strong and a weak natural stimulus may be cited by having a small strip 
of dull-grayish paper placed in juxtaposition to a similarly sized strip of a 
bright-green paper, in which case, after some seconds’ exposure, the 
border of the dull-gray strip next to the bright-green will have a reddish 
cast.2 
The so-called “ multiple complements,” or rather “ alternating subjec- 
tive after-colors,” as, for instance, in the following example, where alter- 
nating subjective perceptions of green and of red have been aroused by 
1 “ On the Blending of Colors by the Sole Agency of the Sensorium.” By John Gor- 
ham, M.R.C.S., Tunbridge; Brain : A Journal of Neurology, vol. iv. p. 467. As early 
as 1808 Sir David Brewster obtained similar results in an almost identical way. ( Vide, 
p. 257 of the first American edition of A Treatise on Optics. By Sir David Brewster, 
LL.D., F.R.S.L. & E., etc., Philadelphia, 1845. 
2 These experiments might be multiplied almost indefinitely in different ways, with 
varying though corresponding results. Buffon, Schaeffer, Westfield, Chevreul, Brew- 
ster, etc., have all given a great number of interesting modifications of this variety of 
subjectivism. 122 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
sensory and perceptive materials set into activity through the action of 
either a recognized objective natural green color or a subjective green in 
producing a red subjective after-color, are most probably dependent upon 
momentary alternating regains and discharges of sufficient energy mate- 
rial to perceive color energies equal to, first, the primary energy and then 
its subjective after-color, after having had perceived the subjective after- 
color. It is a modification of the same old battle though now transferred 
to the perceptive cells ; the changes in the passing results being dependent 
upon some peculiar condition under which the new variety of weapon is 
wielded. 
So far the first division has been discussed. Endeavors will now be 
made to explain the causes of the different actions coming under the 
second head, where the visual apparatus has either an irritant taking birth 
within itself or a cerebral stimulus to respond to. In the first instance, 
there cannot be any doubt but that it is possible for the subjective after- 
colors to be provoked by an irritant affecting any part of the visual appa- 
ratus. Suppose the following case: sudden squeezing of the sensory 
elements of the transmitting parts of the optic nerve, from some momen- 
tary blood-pressure increase, with a production of the perception of sub- 
jective color. This symptom means that a traumatic stimulus has caused 
a separation of a definite amount of nerve-energy, which specific quantity 
is transmitted and perceived as though it had been set into motion by a 
color-stimulus of external origin. If this traumatic stimulus should be 
continued for a few moments longer, then suddenly dropped, and the visual 
apparatus subjected to another act of traumatism, the second subjective 
visual result would be diminished by as much power as had been extracted 
by the first act of traumatism, and the answer would be equal to the 
amount of difference. If the primary irritating force should transmit all 
of the resident nerve-energy there would not be any perception caused by 
the second force. These rules hold good for any part of the visual appa- 
ratus, no matter whether the exciting stimuli originate in the ocular retina, 
the conducting nerves, or in the cerebral sheet. Under this category 
come the answers to the questions suggested by the production of subjec- 
tive colors when the visual apparatus is not exposed to natural color- 
stimulus. For easy study there have been two subdivisions made : First, 
the production of the so-called complements when the organ of sight is 
in complete darkness; and second, the production of the so-called com- 
plements when the organ of sight is directed against a black surface. 
Practically, these two divisions are the same. The following example 
illustrates a cause coming under the first subdivision. A man walking in 
the dark suddenly strikes his eye against a heavy blunt obstacle. He has 
an immediate subjective perception of red flashes of light. A moment 
later his organ of sight encounters with much greater force a second 1885.] 
Oliver, A Correlation Theory of Color-perception. 
123 
obstacle, and there arises a perception of a subjective green. Here there 
is a blow upon the outer tunics, followed by a stronger second one, each 
causing a contre coup upon the sensory elements of an equivalent nerve- 
energy power; the second blow or stimulus having arrived before a forma- 
tive action for the amount of separated nerve-energy caused by the pri- 
mary act has taken place.1 If white light had been the primary subjective 
color there would not have been any subjective after-color. 
Where subjective colors are produced by changes in cerebral structure, 
or in actions taking their origin within the limits of perceptive material, 
the same reason for cause and effect as expressed in the paragraph upon 
subjective color-changes originating from excitants taking their birth 
within the visual apparatus, must be accepted as truisms, although it 
should be strictly understood that when, in its studies, the human men- 
tality approaches the domain of the cei’ebral forces, and demands answers 
as to the why and the wherefore of the physical changes and the physio- 
logical actions occurring within itself, it assumes a position bordering 
almost upon the search of the infinite. It must be agreed that there are 
two distinct changes taking place in the conversion of a sensation into a 
properly recognized perception. First, an action upon the lower mentality 
by the received sensory result, which has been spread upon the cerebral 
retina, causing a physical change in the contiguous cerebral material, with 
a production of the primary form of a perception. Second, a conversion 
of this automatic perception into a higher form through the action of a 
conveyed and everchanging quality of perception upon a certain amount 
of physical material resident near or in the centres of intelligence. These 
two actions constitute the direct order of the complete evolution of a color- 
perception as well as the last physiological rule of consummated vision. 
If it thus be accepted that the evolved perception of a completely sensi- 
tized color-energy passes through the same character of stations, and is 
subject to the same laws, although now of a higher grade of nerve material 
and cell-action, as it did whilst pursuing its course inwards as a sensation, 
and that similar acts of separation and re-formation as were attributed to 
the production of the completed form of color-sensation in the visual appa- 
ratus occur in the related perceptive elements of the cerebrum, it must 
be admitted that momentary alterations and transitory physical changes 
in these perceptive structures may happen in such a way as not only to 
produce subjective color-images, but actually to make the ego doubt the 
subjective quality. For instance, suppose the production of a subjective 
after-color upon a black surface, after the perception of a natural color 
stimulus. Here the second stimulation upon the perceptive color cells 
1 This example might be multiplied in many ways, and the stimulus made to origi- 
nate in any part of the visual apparatus, but for proper explanation, this selection is 
thought to be sufficient. 124 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
must be of central origin,1 because tlie moment the primary natural force 
is removed there,is absolutely nothing external left to reexcite the exposed 
peripheral terminals of the optic nerve. To explain : Suppose that a small 
square of red color be placed upon a dead-black surface, and a visual appa- 
ratus be allowed to fix upon it for several moments by the aid of a good 
light. Without moving the organ of vision from the point of fixing, have 
the red square suddenly taken away, and the light decreased to almost a 
minimum intensity, and there can be made to subjectively appear a green 
color upon the portion of the dead-black surface previously occupied by 
the red stimulus. In this experiment a portion of the energy material of 
the impinged optic nerve filament tip has been separated, evolved, and 
perceived as red ; whilst a remaining nerve-energy material sufficient for 
the perception of a subjective complement of the transmitted and perceived 
primary nerve-energy has been left untouched. The acting sensory fila- 
ment has been lowered to a transmitting power equal to the amount of 
nerve-energy left in its tip ; whilst the internal termination of the filament 
upon the cerebral retina has been reduced in its power to an amount equal 
to the difference between its normal equivalent and the quotient of value 
of the perceived primary nerve-energy. The sudden removal of the natu- 
ral stimulus, with the substitution of an area that is incapable of throwing 
out any vibrations of natural color, causes an immediate cessation of sepa- 
ration and transmission of the nerve-energy of the primary stimulus, with 
an attempt of formative action commencing in the peripheral tip of the 
abnormalized optic-nerve filament, and passing inwards throughout the 
whole connected extent of the sensory nerve. Before the restitution of 
the nerve-force material has reached the central terminus of the tip’s fila- 
ment, there has arisen an excitant in the cerebral cortex, either through 
will-power or emotion, which excitant has acted upon the acting central 
terminus of the optic-nerve filament, and caused a separation from the 
nerve-energy material remaining in the terminus; thus producing a per- 
ception of a subjective complement of the primarily perceived color. For 
obvious reasons, should the experiment have been tried with a square of 
natural white color, there would not have arisen any true “ subjective 
after-color” at all. If the under larger surface had been gray instead of 
black, there would have been a visible area of subjective darkness, equal 
in size to the removed white square, because in reality in the above ex- 
periment of a white color upon a black surface there is as a result, in 
addition to the great amount of unused sensory nerve terminals, a small 
area of exhausted tips, which area is rendered invisible by reason of the 
non-employment of the surrounding nerve-tips ; whilst in the latter experi- 
ment upon a gray ground there is a sufficient natural sensitizing material 
affecting the surrounding optic-nerve fibre tips to cause the area of non- 
1 This excludes internal forces that may arise in the sensory portions of the visual 
apparatus. 1885,] 
Oliver, A Correlation Theory of Color-perception. 
125 
action to be perceptible. (Had the primary natural white stimulus been 
very strong, there probably might have been a series of passing subjective 
color changes.) 
The same line of reasoning might he used if the primary stimulus had 
been of internal origin ; the only difference being that in this case there 
would not have been any external stimulus whatever. This might be 
illustrated by placing the organ of sight in the dark, and causing a second 
cerebral stimulus to act upon a perceptive color-cell which had been lowered 
by some previous cerebral act. 
All of these observations upon “ subjective after-color,” whether pri- 
marily produced from extraneous or internal stimuli, have dealt with the 
perceptive cells belonging to the most sensitive regions of either the ocular 
retina or the cerebral retina.1 Experiments as to the possibility of the pro- 
duction of subjective after-colors through the peripherally placed cells2 would 
be of value; although from the arguments brought forward in this theory it 
is certain that if sufficient intensities and large enough areas could be given 
to two complementary natural colors, or that two internal forces equivalent 
to those from the twro natural complements could be aroused, so that their 
actions would be separately perceived by the eccentrically placed percep- 
tive cell (as we know is possible), the subjective after-color of either of 
the natural colors or of the internal stimuli, could be provoked from the 
remaining energy of the primarily excited cell. 
The other varieties of subjective after-colors are dependent upon modi- 
fications of the just described exciting agencies and conditions of physical 
material. It is for these reasons that no endeavors for their explanation 
have been given. 
Fourth. Color-perception as caused by the action of internal stimuli 
upon nerve-energies which have not been lowered by any preceding act. 
Subjective Color. Under this heading come all those visible expressions 
of actions upon unused perceptive color-cells, through internal force set 
into activity by internal agencies. It differs from the preceding head in 
the fact that the color-perceiving cell has not been lowered in its individual 
forces by any previous act upon its nerve energy material. Here there 
is not a “ remaining energy” ; the energy is in its entirety, and ready to 
give subjective visible expression to any color that it has once known ob- 
jectively. If the material of the nerve energy should be of the finest type, 
and its visible white of the purest variety, then the more individual color 
1 As this theory presumes a central as well as a peripheral expansion of the visual 
apparatus analogous to the roots and branches of a tree, it does not seem unjustifiable 
to speak of the most sensitive region of the cerebral retina, when it is remembered that 
the individual components of the two retime bear equivalent physical and physiological 
relations with each other. 
2 By “peripherally placed cells” is meant the probable position upon the cerebral 
cortex of those perceptive color-cells which are the internal representatives of the optic- 
nerve filaments of the circummacular regions of the ocular retina. 126 
Oliver, A Correlation Theory of Color-perception. 
[Jan. 
gradations it has under its jurisdiction, and the more subjective colors can 
be separated from it for perception. This presumes that there is no con- 
genital or hereditary mental power, and that all mental force must have 
been derived from the external world. (The true reason of “ Hereditary 
Genius” is, that one brain may have a more highly developed material 
structure, or a stronger physical substance devoted to certain mentalities 
than another brain, and that the first organ by an equivalent amount of 
physiological action as the second, may be productive of better work than 
its less fortunate companion ; marking the possessor of the better built 
machinery as a remarkable “ color-seer,” or a fine “ sound-hearer,” etc. 
If the individual who possesses this better substance should persist in an 
avocation fitted for the constant use of such structures, he will cause rapid 
increase of physical material in the parts, and thus through extra powers 
of receipt and response be brought into eminence.) This is the true 
foundation of the superiority of one perceptive color-cell material over that 
of another similarly placed and used cell. This is the reason that there 
must be different grades of subjective colors dependent upon the strength 
of variously placed nerve energies and provoked internal stimuli, just as 
there were differences in objective colors dependent upon the value of the 
receiving fibre, as well as the amount and character of natural stimuli. 
Internal stimuli acting upon responsive perceptive material may be assumed 
in many ways, sucli as through sudden vascular changes, or by momentary 
pressures upon sensory tissue. That this is actually so, is fairly presum- 
able from the everyday experiences of the victims of the visual types of 
either “conscious centric (or subjective) pseudopia,” or “unconscious 
centric (or subjective) pseudopia,” 1 or of “ Hallucinations,” as Hammond2 
prefers to call them. Yet as it is neither in the province nor in the scope 
of this paper, to enter more fully into this part of the subject than will be 
sufficient for explanation of the causes of a few of the prominent varieties 
of subjective color, all others will be set aside, so as to allow deductions to 
be drawn from the chosen examples. The varieties will be primarily 
divided into two groups—the physiological and the pathological. The 
former will be treated of here, whilst the latter will be reserved for the 
third portion of the paper, in order that the various causative stimuli of 
abnormal nature may be placed in their proper and respective groupings.3 
1 These terms first made use of by Dr. Ed. H. Clarke, in an excellent, though un- 
finished essay upon “Visions: a Study of False Sight (Pseudopia).” Boston, 1878, 
8vo., pp. 315. 
2 Divided into two kinds, “ recognized” and “ delusive.” “ Diseases of the Nervous 
System.” By Wm. A. Hammond, M.D. 
3 Strictly speaking, hallucinations occurring when the visual apparatus is impressed 
by natural color, as in ordinary daylight, should be considered as having been caused 
by actions upon remaining nerve-energies in previously impinged perceptive color- 
cells. 1885.] 
Oliver, A Correlation Theory of Color-perception. 
127 
Physiologically, it does not matter in what internal situation the abnor- 
mal stimulus originates. If there should be a momentary attack upon any 
perceptive color-cell, there would be an immediately perceived action. For 
instance, the sudden appearance and disappearance of phosphenes from some 
internal momentary blow upon the region of perceptive color-cells, when the 
visual apparatus is either in a dark room, or when it is directed against a 
black surface.1 Here there is a physiological action of a properly charged 
color-cell, from an abnormal process of stimulation. The physiological 
action of the cell is perfect, and the amount of action is dependent upon the 
force of the internal stimulus. 
The same explanation holds good should an experiment be made by 
which a subjective color should be projected from an unused sensory fila- 
ment upon a black surface, or into a dark space, during the time that it« 
contiguous filaments are being exposed to strong intensities of natural 
color for some length of time ; the only difference being that here there is a 
change in the kind of natural cause, and the character of its invasion. 
At first sight, it may appear as if it should in reality have been placed 
under the preceding head “subjective after color,” but upon making sepa- 
ration of the reasons for the various manifestations, the proper situation 
will be found to have been chosen. Here there is a strong internal 
stimulus from the perceptive cell of the strongly impressed sensory fila- 
ment acting upon the unused perceptive cell of the unimpinged second 
sensory filament, giving a definite and equivalent response in the percep- 
tive cell of the second sensory filament. This does not in any way mean 
that there is an action of a “ remaining energy” of the perceptive cell 
which has been impinged by the internal force, but that the internal 
stimulus from the primarily lowered perceptive cell is of a complementary 
type. 
Reasoning from these lines of argument, it can be assumed as a certainty 
that the latter experiment might have been so modified as to cause sub- 
jective colors to appear to an unexposed second eye, because even here 
there is a definite amount, and a definable source of stimulus to attack the 
working material of the unused organ.2 
1 The origin of this force may have been external, as from a blow upon the vault oi 
the cranium. 
2 At this point, “ physiological research” is ended. In the concluding paper, which 
will appear in the April number of this journal, “pathological data in support” and a 
“ resuu<£” will be given. Kemper, Lodgment of a Breech-pin in the Brain. 
[Jan. 
Article IX. 
A Case of Lodgment of a Breech-Pin in the Brain ; Removal on the 
Second Day : Recovery. By G. W. H. Kemper, M.D., of Muncie, 
Indiana. 
On the 19th day of April, 1884, Emerson McC., a robust farmer boy, 
aged 18 years, received a compound fracture of the frontal bone, imme- 
diately above the right frontal sinus, by a bursting gun. About noon, as 
ascertained from persons who heard the report of the gun, while the 
weapon was in position before his face, lie fired at a squirrel. Four hours 
later he made his way, unaided, to his father’s home. An investigation 
revealed the facts that the accident had occurred one-lialf a mile from the 
home, the gun had been broken into numerous pieces, and he had lain on 
the ground for a considerable length of time in an insensible condition. 
The hemorrhage had been moderate in quantity, and about half a tea- 
spoonful of brain substance was found upon the leaves. 
Dr. D. O. Munsey, of New Corner, the family physician, was sum- 
moned, and arrived about six o’clock. He found the patient suffering but 
little pain, and his mind was clear. Cold water dressings were applied— 
a critical examination of the wound being postponed for a consultation. 
At 9 A.M. of the 20th—about twenty-one hours after the receipt of the 
injury—I saw the patient. The temperature was 104|° ; pulse 64. He 
felt but slight pain, and the mental faculties were unclouded. He had 
slept well during the night. The tissues around the right eye were con- 
siderably swollen, and blackened with powder stains. A partially curved 
wound, about one and a half inches long, was located vertically above the 
right eyebrow. Raising the valve-like flap of skin, I found quite an aper- 
ture through the two plates of the frontal bone. Passing my 'finger 
through this and into the brain to search for any pieces of bone that 
might be detached, at a distance of half an inch beyond the internal 
plate, I felt a serrated object, and, guided by my finger, I introduced a 
dressing forceps, and seized and withdrew it—the breech-pin of a gun. 
I presume the characteristic shape of the wound of the skin and soft 
tissues wfs made by the iron striking with its long diameter. After en- 
tering the cranial cavity the base of the pin advanced, and left the small 
end towards the point of entrance, and this was the point I first touched. 
Some five or six small pieces of detached bone were removed at this time, 
and two or three more, with a piece of his felt hat, worn at the time of the 
accident, appeared at the opening of the wound, sevexal days later, and 
were removed by Dr. Munsey. 
During all the time of my manipulations the patient made but slight 
complaint of pain—having refused to inhale an anaesthetic. The shape 
and natural size of the iron is shown in the accompanying cut (Fig. 1). 
The iron weighed 617 grains; length, inches. THE MEDICAL NEWS. 
A National Weekly Medical Periodical, containing 28-32 Quarto Pages 
in each Number. Published every Saturday. 
Uniting the scholarship of a weekly magazine with the energy of a daily news- 
paper, The Medical News renders a service of especial value to the profession. 
As a magazine, it contains Original Articles and Lectures by the ablest writers 
and teachers of the day, judicious Excerpts and Translations from the medical, 
pharmaceutical and scientific periodicals of the world, and numerous Editorials 
from the pens of a large and able Editorial Staff. As a newspaper, it maintains 
a corps of reporters and correspondents, in all the medical centres of the globe, 
and receives by mail and telegraph prompt and accurate reports of Society Meetings 
and other matters of immediate interest. It is thus enabled to present in each 
issue, without loss of time, the advance of knowledge attained in the medical 
sciences during the previous seven days. Ample space is devoted to News Items and 
Correspondence and to the weekly official list of changes in the Army and Navy 
Medical Departments. In typographical arrangement everything has been done 
to economize the time and to promote the comfort of its readers. The subscription- 
price of The News has been fixed at the very low sum of Five Dollars per 
annum. 
The American Journal of the Medical Sciences. 
A Quarterly, Published on the first days of January, April, July and 
October, each Number containing over 800 large 
Octavo Pages, fully illustrated. 
Founded in 1820, The American Journal now begins its sixty-sixth year of 
faithful and honorable service to the profession, with full assurance of con- 
tinuing usefulness. The great amount of space devoted to Original Articles 
enables it in each issue to present a large number of elaborate papers, embracing 
in scope all departments of medical science. The Reviews have always been noted 
for their impartiality and discernment, and the Quarterly Summary of Improvements 
and Discoveries, classified under appropriate heads, is highly valued as an accurate 
and convenient summary of medical advance. The subscription price of The 
American Journal has never been raised during its long career; it is still 
furnished for Five Dollars per annum. 
Together, The American Journal and The Medical News contain ar 
equivalent.of over 4000 octavo pages, in which duplication of matter is preventec 
by special management. They will be furnished together at a commutation rat* 
of Nine Dollars per annum, in advance. 
The safest mode of remittance is by Bank Check or Postal Money Order, 
drawn to the order of the undersigned; where these are not accessible, remittances 
may be made at our risk by forwarding in Registered Letters. Address, 
706 & 708 Sansom Street, Philadelphia. 
LEA BROTHERS & CO.,