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

by Xavier Bichat

In other circumstances the brain is only affected sympathetically. In many acute affections what is called translation to the brain, does not arise from more blood being carried to it; the pulse is not fuller, the face is not more flushed; there are often even signs of languor in the action of the vascular system. The brain is affected, like all the other organs by sympathy, a happy word, which serves to veil our ignorance in respect to the relations of organs to each other; the brain is affected then like the heart, the liver, &c. Take for example peripneumony; the lungs are then the organs that are essentially injured, from this essential and local injury, arise many sympathetic ones more or less severe. If the liver is sympathetically affected, bilious symptoms are joined to the symptoms of the principal affection; if it is the stomach then gastric symptoms are manifested. The heart is always agitated; hence there is fever. When the sympathetic influence extends to the brain, there is violent motion, convulsions, &c.; for, as I have said, the state of the muscles is the index of the state of this organ; now, in this last circumstance, the will has nothing to do with the animal contractility in exercise; the patient cannot prevent the convulsive agitation of his muscles; the sympathetic irritation of the brain is stronger than the influence of the will. This example of cerebral affection in peripneumony, though more rare than in many other diseases, may however give us an idea of what takes place in all other cases in which the muscles are convulsively agitated by the injury of any organ, by that of the fibrous system distended, of the ligaments and especially of the aponeuroses, by dentition, by violent pains in the kidneys, in the salivary glands or the pancreas, occasioned by a stone, by injuries of the diaphragm, the nerves, &c. In all these cases, there is an affected point in the economy; from this point the sympathetic irradiations go off, which especially reach the brain; this irritated by them, enters into action and excites the muscles; their contraction takes place and the will is a stranger to it.

See also how the passions which have their influence particularly over the internal organs, which especially affect those placed around the epigastric centre, the heart, the liver, the stomach, the spleen, &c. imprint on our motions an impetuosity, which the will cannot make us masters of. The internal organ affected re-acts upon the brain, this excited stimulates the muscles; they contract, and the will is almost nothing in this contraction. Observe the man, whom jealousy, hatred or rage agitates to the greatest degree; all his movements follow each other with an impetuosity which judgment reproves, but which the will cannot moderate, so much does the influence of the sympathetic affection of the brain predominate over that of the will. At other times the passions exhibit an opposite phenomenon. They are marked by a general weakness of all the muscular motions. In astonishment accompanied with grief, or in that in which is mixed a lively joy, the arms fall down as it is commonly expressed; the cerebral influx ceases almost entirely, and yet it is not to the brain that the influence of this passion is carried, it is to the epigastric centre, as is proved by the sudden contraction which is felt there. One of the epigastric organs has been affected; it has reacted upon the brain; this has been interrupted in part in its functions; the muscles feel it and theirs cease. In fear in which this phenomenon is observed, as the paleness of the skin indicates the languor of the circulating system, it may happen that the cerebral and muscular inaction arises in great measure from this, that there is not received a sufficient impulse from the heart, upon which the first influence of the passion is exerted, and which by this influence is retarded in its motions. Fear, it is said, takes away the legs, petrifies, &c.; these expressions, borrowed from vulgar language, indicate the effect of this passion on the muscles; but this effect is only secondary; the first influence has been upon the heart, the second upon the brain; it is not till after the other two that the muscles are affected. Hence how certain animals remain immoveable at the sight of that which is about to seize them for its prey.

It is also to the sympathetic influence of the internal organs upon the brain, that should be attributed the motions of the fœtus, motions which the will does not direct; for the will is but a result of the intellectual phenomena; now these phenomena are nothing at this period of life. The internal functions then very active, suppose a great action in the liver, the heart, the spleen, &c.; now these organs in that way influence efficaciously the brain, and this in its turn puts the muscles in motion; so that the animal contractility is by no means voluntary in the fœtus; it does not begin to become so until the sensations have brought into action the phenomena of the understanding; until then, they must be compared to all those of which we have spoken above.

From all that has just been said, it will be easily understood, I hope, how the animal contractility can be or not subjected to the influence of the will. In both cases, the series of phenomena which it requires is always the same; there is always excitement by the brain, transmission by the nerves, execution by the muscles, or successive inactivity of these three organs. The difference is only in the cause which produces the cerebral excitement; now this cause can be, 1st, the will; 2d, an irritation immediately applied; 3d, a sympathetic irritation. It is essential to form precise and exact ideas concerning this vital force which performs so great a part in the living economy.

Duration of the Animal Contractility after Death.

The difference of the causes which act upon the brain in the animal contractility, in order to determine it to excite the muscles, appears particularly in a remarkable manner at the instant of death. Whatever may be the way in which this happens, the intellectual functions are always the first to cease; it is even to this that we especially attach the idea of the absence of life. Whence it follows that the first phenomenon of this absence must be the failure of the muscular contraction subjected to the influence of the will, which is the result of these intellectual functions. Every thing then remains immoveable in the muscular system, if no other cause acts upon the brain or the nerves; but these two organs are, yet for a long time, capable of answering to the various excitements of stimuli. Stimulate in any way the brain, the spinal marrow or the nerves of an animal recently killed, in an instant its muscles convulsively contract; it is the same phenomenon as that obtained during life from the same cause. Often even immediately after death, this phenomenon is still more apparent than during life; I have been frequently convinced of this in my experiments. If during life we irritate any nerve, the contraction oftentimes is almost nothing, because the will acting by the other nerves upon the same muscle, or at least upon those of the limb, produces contractions opposite to those which the irritation tends to produce. I have many times observed that the galvanic phenomena are also infinitely more easily produced an instant after death, even in animals with red and warm blood, than during life; in this last case often we can obtain hardly any result, because their influence is counteracted by the cerebral influence arising from the will. When the irritation is directly applied to the brain or the superior part of the spine, it then surpasses the will; it is stronger in the living animal; but on an insulated nerve, it is often inferior to it; not that the will acts by the irritated nerve, its influence in it is arrested at the place stimulated, but it exerts itself by the adjacent nerves.

It is to the susceptibility of the brain and nerves of still transmitting the principle of motion after death, that must be referred all the phenomena that are witnessed in the different kinds of decapitation. Ducks, geese and other animals of this family move their muscles with some regularity, after the head is taken off, in running, jumping, &c. Some time after the punishment of the guillotine, the inferior and superior extremities are still the seat of various tremors; the muscles of the face are sometimes even contracted so as to give to this part the expression of certain passions, an expression incorrectly referred to the sensitive principle still left for some time in the brain. The same phenomena were formerly observed in the punishment that consisted in cutting off the head with an axe. During the year past I have had a painful proof of these singular facts; a guinea-pig, whose heart I had just removed, plunged deep into my finger the four prominent teeth that distinguish this species. All these phenomena are only the result of the irritation produced, either by the cutting instrument, or by the air, upon the two divided extremities of the marrow; this is so true, that by increasing the irritation by a pricking, cutting instrument, &c. with a chemical agent applied to these extremities, the motions are very much increased. Nothing is more easy than to be convinced of this fact in an animal; I have many times proved it in those who have been guillotined, upon whom I have been allowed to make experiments for galvanic purposes. See how the alternate motions of respiration can continue for some time, after the brain has been destroyed, after a wound of the head in which its mass has been crushed, after a luxation of the first vertebra, in which the beginning of the spinal marrow has been compressed so as suddenly to stop life, after the injection of a very irritating fluid by the carotid, &c. &c.

In this duration of animal contractility after death, the muscles are absolutely passive; they obey, as during life, the impulse they receive from the nerves; it is this which distinguishes it essentially from the duration of irritability, a property by which, after death as during life, the muscle has in it the principle which makes it move.

The duration is greater or less according to the class of the animals; those with red and cold blood keep this property longer than those with red and warm blood; among these, the family of ducks are, as I have said, remarkable for this phenomenon, which is much more rapidly lost in the others and in quadrupeds. In the first class there are also varieties among the reptiles, fishes, &c.

In general I have constantly observed that the animal contractility ceases after death, first in the brain, then in the spinal marrow and last in the nerves. When the muscles no longer move by irritating the first of these organs, they contract by stimulating the others. The irritated nerves can still communicate a motion, when the spinal marrow, no longer exhibits this phenomenon. I have not observed that the superior part of the nerve ceased sooner to transmit motion, than the inferior. But what is remarkable is that certain nerves, under the influence of the same irritation, make their muscles contract more strongly than others; such for example is the phrenic. When all the other muscles cease to be moveable by the artificial excitement of their nerves, the diaphragm is still moved by this means. Whilst experiments have but little effect elsewhere, they are in full force upon this muscle; this is the more remarkable, as during life this is precisely the one which is the least affected by the state of the brain and the spinal marrow; paralysis and convulsions hardly ever affect it, as we have seen.