Psychology Applied To Medicine

PROFESSOR LADD has defined psychology as ” the science which describes and explains the phenomena of consciousness.”

While abstruse logic and cosmic philosophy are still legitimate departments of the subject, the new psychology is not strictly metaphysics, it is a physiological psychology, in fact a mental physiology. The very word experimental, as applied to the subject, suggests appliances and individual research quite beyond the scope of logic.

It is a recognition of the law laid down by Professor James, that ” no mental modification ever occurs which is not accompanied or followed by a bodily change,” which renders it imperative that a physician should be well grounded in the fundamental truths of psychology.

The comprehensiveness of the subject is overwhelming. The present essay is an attempt to pre-sent only a few well-recognized facts which bear directly on the subjects of physiology and hygiene.

It may be well at the outset to have a clear idea of our limitations. The old controversy between the spiritualist and the materialist is perhaps not yet ended, but there has been a decided reaction from the ultramaterialism of fifty years ago. The attempt to identify thought and molecular motion has few defenders today. It used formerly to be said by this class of thinkers : ” The brain secretes thought as the liver secretes bile.” This is a distressing confusion of two distinct realms in nature, the psychical and the physical.

Recent developments in neurology have thrown much light on the phenomena of brain activity. Cerebration is now thought to be accompanied by a temporary association of nerve cells; but were we able to trace the nervous impulse, thru all its intricacies, to the brain centers, did we know the exact molecular changes which cause the efferent impulse, — the nature of a thought would be as much a mystery as ever. Indeed it is doubtful if the question is ever solved by the finite mind. Tyndall said : ” There is no fusion possible between the two classes of facts. The passage from the physics of the brain to the corresponding facts of consciousness is unthinkable.”

It is not claimed that the unknown is necessarily the unknowable, but it is a line of investigation which cannot be taken up in any superficial way. This confession of ignorance is in fact a great step toward a higher knowledge. It is a refined agnosticism. The fact seems to be that the brain is the organ of the mind, just as the body is the organ of the brain.


Simple protoplasm possesses irritability, contractility, and elasticity — that is, it has sensation equal to its needs. Professor Sutherland has said : ” A nervous system is an arrangement by means of which an organism becomes conscious of its environment (food, friends, and foes) and adapts itself thereto.”

This is a very comprehensive definition suited to any form of life except unicellular organisms, and even here, aitho there is no aggregation of nerve elements into a system, yet monocellular forms react to touch, pressure, etc.

When the ameba envelops and ingests the food particle that touches its periphery, it evidences a ” consciousness of environment and adjustment thereto.” It is evident that the word consciousness is here used in a general sense. Some psychologists have restricted the term to define a human attribute only, and others have asserted that consciousness without a central nervous system is impossible. From a biological standpoint all life is conscious.


By studying the evolutionary scale of life as it exists today, it is seen that the nervous system, like its accompanying organism, progresses from the simple to the relatively complex, till in man it reaches a development capable of what we call reason.

Undoubtedly psychology has drawn too sharp a line between reason and instinct. The reaction from this was the contention that the lower animals reason, the difference being one of degree, not of kind. The earlier idea that reasoning was an attribute of man only was natural in preëvolutionary times, and was based on the belief in the immediate creation of perfected organisms, the so-called special creation, because special creations had distinct endowments. The evolutionist maintains that since the establishment of the general law, ” from the simple to the relatively complex,” the burden of proof rests on him who claims that at any time or place it ceases to be of universal application.

Perhaps no one has a right to affirm that gravitation is of universal application, and yet experience warrants one in assuming its universality as a working hypothesis till an exception is proved. So it is assumed that the development of the nervous system has been one continuous upward movement, till we have the mind of man. This would lead us to expect to find the difference between reason and instinct one of degree, and in the last analysis this may be so. Evolution teaches that certain species have become side-tracked, and are forever con-signed to inferior positions. These are the animals whose mentality never rises above the plane of instincts. As morphological connecting links are wanting, so in a still more emphatic way is there a gulf between the highest instinct and the human mind.

Professor James says : ” No actions but such as are done for an end, and show a choice of means, can be called indubitable expressions of mind.” Accepting this criterion, that in order to be classed as reason an act must ” show a choice of means,” it is possible to draw a sharp line between reason and instinct.

It is somewhat generally believed that instincts are attributes of the lower animals only, and the fact is overlooked that man is richly endowed in this direction, especially in infancy. Instincts are impulses. ” Theirs not to reason why.” In physiology we call them reflexes. The human infant is born with the instinct to suck fully developed. The tendency to clasp any object that comes in contact with the fingers or toes is very marked. In fact, this instinct is stronger a few hours after birth than at any later period.

New-born children are able to sustain their own weight by grasping a lead-pencil, often with only one hand. The evolutionary bearing of this is very interesting, and shows very beautifully how natural selection could, in the lower animals, propagate this impulse. The young of the chimpanzee whose grasp of the mother was strongest would by this means escape destruction when pursued by an enemy. Of course in man the law of the ” survival of the fittest ” is operative in a lesser degree. The transiency of many infantile instincts, when not exercised, will be again referred to under the subject ” Habit.” Fear and love we possess in common with the animals. The sexual passion is perhaps one of the strongest examples.


Let the great John Burroughs answer it.

” Apropos of the question, ` Do animals think? ‘ a correspondent, writing from Washington, says that I deny this power to the lower animals because I use the word in a too restricted sense. He then proceeds to say that if we use the word ` chin ‘ to signify ` exclusively a portion of the human face, meaning that portion which is extended perpendicularly downward from the mouth, we would hesitate to say that lower animals have chins. So if we define ” laugh” as spreading the mouth in merriment we could not say that animals laugh.’

” I am quite ready to admit that animals think in as strict a sense as they have chins or as they laugh. A feeling of play and merriment they certainly have, but this feeling is practically entirely physical. I don’t suppose an animal could appreciate a joke, or the comic, or the absurd. Man is the only animal that laughs or weeps, though tears may run from the eyes of a suffering beast. And the chin of a bird or beast is a very rudimentary affair indeed.

” Take the case of the little yellow warbler when the cowbird drops her egg into its nest — does any-thing like a process of thought or reflection pass in the bird’s mind then? The warbler is much disturbed when she discovers the strange egg, and her mate appears to share her agitation. Then after a time, and after the two have apparently considered the matter together, the mother bird proceeds to bury the egg by building a new nest on top of the old one. If another cowbird’s egg is dropped in this one, she will proceed to get rid of this in the same way. This all looks very like reflection. But let us consider the matter a moment. This thing between the cowbird and the warbler has been going on for innumerable generations. The yellow warbler seems to be the favorite host of this parasite, and something like a special instinct may have grown up in the warbler with reference to this strange egg. The bird reacts, as the psychologists say, at sight of it, then she proceeds to dispose of it in the way above described. All yellow warblers act in the same manner, which is the way of instinct. Now if this procedure was the result of an individual thought or calculation on the part of the birds, they would not all do the same thing; different lines of conduct would be hit upon. How much simpler and easier it would be to throw the egg out – how much more like an act of rational intelligence. So far as I know no bird does eject this parasitical egg, and no other bird besides the yellow warbler gets rid of it in the way I have described. I have seen a green-backed warbler rearing the young cowbird.

” Another correspondent is sure his dog thinks when he sits up in front of him while he is reading, and taps him on his back or leg as a reminder that he wants the ball in his master’s pocket to play with ; and that his parrot thinks when, on hearing him enter the house, it begins savagely to bite its cage and to make hideous noises, all with a view to obtaining its freedom, so that it can make its way to its beloved master, and caress and play with him. If such things indicate powers of thought, then nearly all animals think. The bee does when it goes forth from the hive in quest of honey; the big midsummer spider does when it shakes its net to frighten you away; the mother bird does when she flutters over the ground at your feet to decoy you away from her nest, etc. But none of these acts can properly be called the result of thinking.

” When a parrot takes a crust of bread and soaks it in its cup of water before eating it, that looks much more like the result of a mental process.”

There are many instances of animal sagacity which seem to show a certain degree of reasoning.

The following is quoted by Professor James:

” I have two dogs, a small, long-legged pet dog, and a rather large watch-dog. Immediately beyond the house court is a garden, into which one enters through a low lattice gate which is closed by a latch on the yard side. This latch is opened by lifting it. Besides this, moreover, the gate is fastened on the garden side by a string nailed to a gate-post. Here, as often as one wished, could the following sight be observed. If the little dog was shut in the garden and wanted to go out he placed himself before the gate and barked. Immediately the large dog in the court would hasten to him and raise the latch with his nose, while the little dog on the garden side leaped up, and catching the string in his teeth, bit it thru.

” Certainly reasoning here seems to prevail.

” In face of it, however, and altho the dogs arrived of themselves and without human aid at the solution of the gate question, I am able to point out that the complete action was pieced together out of accidental experiences, which the dogs followed, I might say, unconsciously.

” While the large dog was young, he was allowed, like the little one, to go into the garden, and therefore the gate was usually not latched but simply closed. Now if he saw any one go in he would follow by thrusting his snout between the gate and the post, and so pushing the gate open. When he was grown I forbade his being taken in, and had the gate kept latched. But he naturally still tried to follow when any one entered, and tried in the old fashion to open it, which he could no longer do. Now it fell out that once, while trying, he raised his nose higher than usual, and hit the latch from below, so as to lift it off its hook, and the gate opened. From thence-forth he made the same movement of the head when trying to open it, and of course with the same result. He now knew how to open the gate when it was latched.

” The little dog had been the large one’s teacher in many things, especially in the chasing of cats, and catching of mice and moles, so when the little one was heard barking, the other always hastened to him.

” If the barking came from the garden he opened the gate to get inside.

” But meanwhile the little dog, who wanted to get out, the moment the gate opened slipped out between the big one’s legs, and so the appearance of his having come with the intention of letting him out arose, and that it was simply an appearance transpired from the fact that, when the little dog did not succeed at once in getting out, the large one ran in, and nosed about the garden, plainly showing that he had expected to see something there.

” In order to stop this opening of the gate, I fastened a string on the garden side, which, tightly drawn, held the gate firmly against the post, so that if the large dog raised the latch, and let go, it would every time fall back on the hook, and this device was successful for quite a time, until it happened one day that on my return from a walk upon which the little dog had accompanied me, I crossed the garden, and in passing through the gate the dog remained behind, and refused to come to my whistle.

” As it was beginning to rain and I knew how he disliked to get wet, I closed the gate in order to punish him in this manner.

” But I had hardly reached the house ere he was before the gate, whining and crying most piteously, for the rain was falling faster and faster. The big dog, to whom the rain was a matter of indifference, was instantly on hand, and tried his utmost to open the gate, but naturally without success. Almost in despair, the little dog bit at the gate, at the same time springing into the air in the attempt to jump over it, when he chanced to catch the string in his teeth. It broke and the gate flew open. Now he knew the secret, and thenceforth bit the string whenever he wished to get out, so that I was obliged to change it.”

If every story of animal intelligence could be carefully analyzed and the history of its development known it would probably be evident, as in this case, that the mentality displayed was hardly worthy the name Reason. There is an association of means and end. The dog remembered that a certain result followed a certain action. In the first instance, when the gate was not hasped, simply pushing against it caused it to open. Accidentally discovering that raising the hasp with his nose, the result — open gate — followed, simple memory of the association of the two occurrences caused him to repeat the movement. To this class of phenomena psychology has given the name Recept. This word is derived from Latin re (back), capio (to take), meaning something remembered.

This is in distinction from the larger word Concept, from the same root, but the prefix con, together, shows that it covers the association of things received. This term is applicable only to reasoning. In reasoning we put things together and pick out the essential quality of observed facts. In this instance, that the pushing of the gate must take place while the hasp was lifted, so that the hasp would not drop into its place again. Then there is formed in the mind a concept, the principle of hasps in general, and the test of a concept is the power to use the idea under similar circumstances.

This leads to Professor James’ proposition : ” The ability to deal with novel data is the technical differentia of reasoning.” This is very well shown by the further history of the two dogs which I quote again :

” That the big dog in raising the latch did not in the least know that the latch closed the gate, that the raising of the same opened it, but that he merely repeated the automatic blow with his snout, which had once had such happy consequences, transpires from the following :

” The gate leading to the barn is fastened with a latch precisely like the one on the garden gate, only placed a little higher, still easily within the dog’s reach.

” Here, too, occasionally the little dog is confined, and when he barks the big one makes every possible effort to open the gate, but it never has occurred to him to push the latch up. The brute cannot draw conclusions, that is, he cannot think.”

These recepts might be defined as acquired instincts, or if that seems a contradiction of terms, acquired reflexes. It is certainly one step higher than the primary instincts, and is quite suggestive of the way in which our ancestors may have repeated certain actions till a tendency to do the same appeared in the offspring. The reason for many of our human instincts is now lost. Yet it never occurs to us to question these actions in ourselves. ” It takes what Berkeley calls a mind debauched by learning to make the natural seem strange, so far as to ask for why of any instinctive human act.”

It was just said that the transmission of acquired habits might account for instincts, animal and human. This was the generally accepted view, altho it was recognized that the evidence was meager in the extreme. But in 1889 Weismann, of Freiburg, published a strong denial, outlining a theory which increases the scope of natural selection.

Weismann denies that functional qualities are transmissible, denies that the blacksmith’s son is capable of any greater physical development than he would have been had his father followed some sedentary profession.

This view has gained many adherents in the intellectual world, and while it would be out of place to introduce the argument here, it must be mentioned that Herbert Spencer was strongly opposed. The principle of inheritance of acquired characteristics is part of the groundwork of his Synthetic Philosophy, and in the later controversy 3 with Weismann he held his ground manfully.

What we need is to bear in mind the fact that we are richly endowed with instincts, and that these form a basis from which are developed habits, habits of reasoning as well as of bodily movements. Reasoning is also based upon experience both individual and ancestral.

Man may therefore be said to be dominated by three sets of impulses.

(r) Congenital reflexes.

(2) Acquired reflexes.

(3) Reason.

The second, acquired reflexes, is a somewhat arbitrary division, and its boundaries are difficult to determine. It is the transitional form, and, altho on its upper and lower sides it merges into the two extremes, its very existence tends to emphasize the gulf between instinct and reason. This difference is thus seen to be not merely one of degree but one of kind. The hights to which human reason may mount are indeed uncomprehensible to the common mind. The vast range of phenomena which a great mind can assimilate at a glance often makes him impatient with us common mortals who have to grope our way step by step. It is frequently quoted that Bow-ditch, who translated one of Laplace’s books, said : ” Whenever his author prefaced a proposition by the words ` It is evident,’ he knew that many hours of hard study lay before him, ere it became evident to him.”‘