General Anatomy, Applied to Physiology and Medicine, Vol. 2 (of 3)

by Xavier Bichat

Animal sensibility is that of all the vital properties which is the most obscure in these organs, at least if we consider them in the ordinary state. Cut transversely in amputations, in experiments upon living animals, they do not experience any very painful sensation; it is only when a nervous filament is touched, that pain is manifested. The peculiar texture of the muscle is but slightly sensible; irritation by chemical stimulants does not show much sensibility in it.

There is however a peculiar sensation, which in the muscles very evidently belongs to this property; it is that which is experienced after repeated contractions, and is called lassitude. After long standing, it is in the thick bundle of lumbar muscles that this sensation is especially felt. After walking, running, &c. if on a horizontal plain, it is all the muscles of the lower extremities which are more particularly fatigued; if on an ascending plain, it is especially the flexors of the ilio-femoral articulation; if on a descending one, it is the posterior muscles of the trunk. In the employments which exercise particularly the superior extremities, this sensation is often experienced in a remarkable manner, which is certainly not owing to the compression made by the muscles in contraction, upon the small nerves which run through them. In fact it can take place without this antecedent contraction, as is observed in the commencement of many diseases, in which it extends in general over the whole muscular system, and in which the patients are, as they say, fatigued and wearied, as after a long march. This sensation appears to depend on the peculiar kind of animal sensibility of the muscles, a sensibility which the other agents do not develop, and which the permanency of contraction renders here very apparent. Thus the fibrous system, sensible only to the means of distension which act upon it, does not receive a painful influence from the other agents of irritation. Observe that this painful sensation, which a too prolonged motion produces in the muscles, is intended by nature to warn the animal to place limits to it, without which the consequences would be serious. Thus the peculiar sensation which arises from distended ligaments, is designed to make the animal limit their extension. Observe how each organ has its peculiar kind of sensibility; how false an idea we should have of the existence of this property, if we judged of it only from mechanical and chemical agents, and observe particularly how nature accommodates to the uses of each organ its kind of animal sensibility.

In phlegmasia of the peculiar muscular texture, the animal sensibility is very often raised to a very great height; the least touch on the skin becomes painful; the patient can hardly bear the weight of the clothes, and frequently the least jar produces in the limbs the most acute pains. But in general these pains are wholly different from the painful sensation which we call lassitude; thus the pain of a ligament stretched in a sound state, is not the same as that which arises from the inflammation of a ligament or any other fibrous organ.

I would add to what I have said above upon this sensation, that some organs are fatigued like the muscles, from too long continuance of their functions; for example, the eyes by the contact of light, the ears by that of sounds, the brain by thinking, &c. and in general all the organs of animal life; it is even this general lassitude which brings on sleep, as I have proved in my Researches upon Life. But observe that the sensation which the eye, the ear, the brain and all the external organs produce when thus fatigued is not the same as that which arises from the over-exertion of the muscles; another proof of the peculiar kind of their sensibility, and in general of that of every living part.

Animal Contractility.

This animal property, upon which all the phenomena of locomotion and voice depend, which assists those of the internal and external functions, has its seat exclusively in the animal muscular system; it is this which distinguishes it from the organic, and from all the others. It consists in the faculty of moving under the cerebral influence, whether the will or other causes produce this influence. The animal contractility has then, like the sensibility of the same species, a peculiar character, differing from the two organic contractilities, a character which consists in this, that its exercise is not concentrated in the organ which is moved, but that it requires also the action of the brain and the nerves. The brain is the principle from which, if we may so say, this property goes, as it is that to which all the sensations come; the cerebral nerves are the agents which transmit it, as they are, though in an opposite direction, the conductors of the sensitive phenomena. Whence it follows, that in order to understand this property well, it is necessary to examine it in the brain, in the nerves and in the muscle itself.

Animal Contractility considered in the Brain.

Every thing in the phenomena of animal contractility proclaims the influence of the brain.

In the ordinary state if more blood is carried to this organ, as in anger; if opium, taken in a moderate dose, excites it slightly; if wine produces the same effect, the muscular action increases in energy in proportion as that of the brain is thus increased. If terror by retarding the pulse, by diminishing the force of the heart, and even the quantity of blood sent to the brain, strikes it with atony; if the different narcotics, carried to excess, produce the same effect; if wine prevents its action by its too great quantity, then observe these muscles languish in their motion and experience even a remarkable intermission. If the brain is wholly engrossed in its relations with the senses, or in its intellectual functions, it, if we may so say, forgets the muscles; these remain inactive; the man who looks or hears with attention, does not move; neither does he who contemplates, meditates and reflects. The phenomena of ecstasy, the history of the studies of philosophers, often present us with this important fact, this muscular inertia, the principle of which is in the distraction of the cerebral influence, which does not increase in other functions, only by diminishing in locomotion.

In diseases, all the causes which act strongly on the brain, re-act suddenly on the animal muscular system; now this reaction is manifested by two opposite states, by paralysis and by convulsions. The first is the indication of diminished energy, the second that of increased; one takes place in compressions from pus, effused blood, bones driven below their natural level, and from the consequences of apoplexy; it is seen in the attack of most hemiplegias, a sudden attack in which the patient falls down, loses all consciousness and has all the signs of a cerebral lesion. This lesion disappears, but its effect remains, and this effect is the immobility of a part of the muscular system. The other state or the convulsive, arises from the various irritations of the cerebral organ from osseous fragments driven into its substance, from its own inflammation or that of its membranes, from different tumours of which it may be the seat, from organic lesions that it may have, lesions which I have rarely observed in the adult, but which infancy sometimes exhibits, and from the causes even of compressions; for oftentimes we see this convulsive state existing at the same time with different effusions, with hydrocephalus, &c.