Claude Bernard

“ How, indeed, can one understand that it is permitted to the physiologist to succeed in explaining the phenomena that occur in all the organs of the body, except a part of those that occur in the brain? Such distinctions cannot exist among vital phenomena. Unquestionably they present very different degrees of complexity, but they are all alike in being either soluble or insoluble by our examination; and the brain, marvellous as those metaphysical manifestations that take place in it appear to us, cannot form an exception among the other bodily organs. ”

“ Besides, do we not find that certain poisons, such as opium and curare, paralyze the nerves and the brain, without being able to discover any visible alteration in the nerve-substance? Yet we are sure that such alterations exist; for, to admit the contrary, would be to admit an effect without a cause. When the poison has ceased to act, we find the mental disturbances disappear, and the normal condition return. It is the same when pathological injuries are healed; the trouble in the intelligence ceases, and reason comes back. ”

“ Reflecting, now, on the organic and physico-chemical conditions required for the support of life and the discharge of its functions, we find that they are the same in the brain as in all the other organs. The blood acts on the anatomical elements of all the tissues by supplying their indispensable conditions of nutrition, temperature, and humidity. When a diminished supply of blood flows to any organ, its activity of function declines, and the organ rests; but if the blood is quite cut off, the elementary properties of the tissue slowly change, while at the same time its function perishes. ”

“ THE first task of physiology was to localize the functions of life in the various organs of the body which serve as their instruments. Thus digestion was assigned to the stomach, circulation to the heart, respiration to the lungs; thus, too, the seat of intelligence and thought was placed in the brain. Still, with regard to the latter organ, a reservation was thought proper, excluding the idea that the metaphysical expression of the intellectual and moral powers was the manifestation, simply and merely, of the cerebral function. ”

“ Every one has long known that, without the brain, intelligence is not possible, but experiment has discovered exactly the part that is played by each portion of the organ. It teaches us that consciousness, or intelligence properly so called, resides in the cerebral lobes, while the lower portions of the brain contain nervous centres destined for organic functions of a lower kind. ”

“ Briefly, then, the brain is governed by the common law that controls blood-circulation in all the organs. By virtue of this law, when the organs are at rest and their action suspended, the circulation in them grows languid; and it increases, on the contrary, as soon as activity is resumed. The brain, I repeat, is no exception to this general law, as had been supposed, for it is now demonstrated that the state of sleep coincides not with congestion, but, on the contrary, with bloodlessness of the brain. ”

“ In the phenomena of general circulation the blood may be said to do nothing more than traverse the parts, to pass from the arteries into the veins; in the phenomena of local, which is the true functional circulation, the blood penetrates all the folds of the organ, and gathers closely about its anatomical elements, to arouse and excite their special mode of activity. The nervous system, sensitive in its action through the vessels, governs all those phenomena of local circulation which attend organic activity ”

“ The progress of modern science has destroyed all such doctrines; yet it must be admitted that those physiologists who have drawn from the most delicate recent researches into the structure of the brain the conclusion that thought must be localized in a particular substance, or in nerve-cells of a determinate form and order, have equally failed to solve the problem, since they have done nothing more, in reality, than to oppose materialistic theories to other spiritualistic theories. ”

“ In a word, the brain has its pathological anatomy exactly as all the organs of the economy have, and the pathology of the brain has its special series of symptoms, just as the other organs have theirs. In mental alienation we observe the most remarkable disturbances of the reason, furnishing in their study a rich mine for the researches of the physiologist and the philosopher ”

“ Experiments have demonstrated that the tissue of the brain exhibits a higher temperature than any other organ of the body. In man and the warm-blooded animals the brain itself produces the heat required for the manifestation of the peculiarities of its tissue. If this were not so, it would infallibly grow cooler, and we should at once see all the functions of the brain become torpid, and intelligence and will perish. ”

“ For instance, when the cerebral lobes of a pigeon have been removed, the animal at once loses its senses, and the power of seeking its food. Yet if the animal is artificially fed, it can survive, because its functions of nutrition continue unimpaired so long as their special nervous centres are left unharmed. Little by little the brain renews itself with its particular anatomical elements, and in the degree in which this restoration takes place we observe the animal's use of its senses, and its instincts and intelligence return. ”

“ In its anatomical development the brain follows the general law; that is, it increases in volume whenever the functions which it controls increase in energy. In the graduated orders of animals we find the brain gain in development in proportion to the greater manifestation of intelligence; and in man, with whom the phenomena of mind have reached their highest expression, the cerebral organ presents the largest volume. The intelligence of the various animals can be readily inferred from the shape of the brain, and the number of creases or folds that extend its surface. ”

“ In this the brain again follows a general law, for in all organs the anatomical element has fixed characteristics by which it may be known; the completeness of the organ consists chiefly in the arrangement of these elements, which presents in every animal species its own peculiar form. Every organ is in fact, then, an instrument whose constituent elements remain identical, while their grouping grows more and more involved in the same degree as the function itself displays more variety and complexity. ”

“ But not only does the outward appearance of the brain change with the modification of its functions; it presents in its inner structure also a complexity that increases with the variety and intensity of the mental manifestations. As regards the texture of the brain, we are long past the days of Buffon, who considered the brains, as he contemptuously called them, a mucous substance of no importance. The advance of general anatomy and of histology has taught us that the cerebral organ possesses a texture more delicate as well as more complex than that of any other nerve-arrangement. ”

“ In this essay, we have attempted to state only one term of the problem, and to show how untenable is the opinion that the brain forms an exception in the organism, and is the substratum of intelligence instead of being its instrument. ”

“ At a later date the lungs were regarded as a sort of furnace to which the mass of the blood repaired successively to gain the heat which circulation was bidden to distribute throughout the body. The advance of modern physiology has proved that all these absolute consignments of vital conditions to special points are chimeras. The sources of animal warmth exist everywhere, and in no region exclusively. It is only through the harmonious functional play of the various organs that the temperature is kept nearly constant in man and the warm-blooded animals. ”

“ The will of the animal persists, but power to guide its motions is gone. In spite of its efforts of will, it moves necessarily in the direction determined by the organic lesion. Pathologists have remarked numerous similar instances in man. Lesions of the peduncles of the cerebellum create rotary movements in men as in animals. Some patients could walk only straight onward. In one case, cruel in its irony, a brave veteran general could only move backward. Therefore the will, which proceeds from the brain, does not take effect on our organs of locomotion themselves ”

“ When the brain of the inferior animals is removed, the function of the organ is necessarily suppressed; but the persistence of life in these beings allows the brain to grow again, and, in proportion as the organ reproduces itself, we observe its functions reappear. The like experiment succeeds in the same way with superior animals, such as birds, in whom intelligence is much more developed. ”

“ When, for instance, we examine the alimentary canal of a fasting animal, we find the mucous membrane that lines the inner face of the stomach and intestines, pale and but little supplied with blood; during digestion, on the contrary, we learn that the same membrane is highly colored, and swollen with the blood which flows energetically into it. These two phases of circulation, in a state of rest and a state of activity, have been brought under direct investigation in the stomach of a living man. ”

“ Diseases, which are at bottom nothing but vital perturbations caused by Nature instead of being produced by the hand of the physiologist, affect the brain according to the usual laws of pathology; that is to say, by occasioning functional troubles which always correspond to the nature and seat of the injury. ”

“ We discover everywhere a necessary bond between the organs and their functions; it is a general principle, from which no organ of the body can escape. Physiology should copy the example of more advanced sciences, and free itself from the fetters of philosophy that would impede its progress ”

“ Anæsthetics, for instance, destroy consciousness and depress sensibility, while they leave the power of movement untouched. Curare, on the other hand, destroys the power of movement, and leaves sensibility and will unimpaired; poisons affecting the heart, suspend muscular contractility, and the oxide of carbon destroys the oxidizing properties of the blood-globules, without at all affecting the properties of the nerve-elements. ”

“ If we seek now to understand the relations that may exist between great activity of blood-circulation and the functional condition of the organs, we shall readily see that this increased flow of the sanguineous fluid corresponds with greater intensity in the chemical alterations going on within the tissues, as also with an exaltation in the phenomena connected with heat which are their necessary and immediate consequence. The production of heat in living beings is a fact established from remote antiquity ”

“ In fact, it has been shown by direct experiment that, during sleep, the brain, instead of being congested, is on the contrary pale and bloodless; while in a state of wakefulness the circulation, becoming more active, provokes a flow of blood proportioned to the intensity of cerebral activity. ”

“ Thus, after a nerve is cut, when the parts to which it had been distributed lose their sensibility, we conclude from this that it is one of the nerves of sensation; if it is motion that ceases, we infer thence that we are dealing with one of the nerves of motion. The same method has been applied in examining the functions of the different parts of the encephalic organ, and, though the complexity of the parts has occasioned novel difficulties of execution, the method has yielded results that are not to be contested. ”

“ The animals subjected to the operation survive it; and observations on their brain through this sort of window, while awake and when asleep, prove that when the dog is asleep the brain is always paler, and that a fresh afflux of blood is regularly noticed on his awaking, when the functions of the brain resume their activity. Facts analogous to those observed in animals have been studied directly in the human brain. Upon a person injured by a frightful railroad accident the effect of a considerable loss of brain-substance was examined. ”

“ Thus, by injuring the peduncles of the cerebellum, and different points of the brain, the experimenter can make an animal move as he chooses, to right or left, forward or back-ward, or can make it turn, sometimes by leaps, sometimes by rotary movement on the axis of its body. ”

“ For the study of the brain in natural sleep a circular trepan is made on a dog's head, and the piece of bone removed is replaced by a watch-glass carefully adjusted to the exact opening, so as to prevent the irritating action of the air. ”

“ There is another and more delicate experimental method, which consists in introducing into the blood various poisonous substances intended to exert their action upon the anatomical elements of the organs, while these are left undisturbed and kept uninjured. ”