Part 46

Besides, in thus comparing the duration of animal contractility, the same stimulant should always be employed; for the effects are more or less evident according to those which we use. When the whole brain and the nerves are no longer sensible to mechanical or chemical agents, they still powerfully obey galvanic impulses. The irritation of the metals is of all the means at present known, the most efficacious in perpetuating animal contractility some time after death.

Organic Properties.

Organic sensibility is the manifest portion of the muscles of which we are treating; constantly brought into action in them by nutrition, absorption and exhalation, it becomes still more apparent, when we irritate muscles that are laid bare; they feel this irritation, and the motion, of which we shall speak hereafter, is the result of this feeling which is centred in the muscle, and which is not referable to the brain.

Insensible organic contractility is the attribute of this muscular system, as of all the others.

The sensible organic contractility is very evident in it. If we lay bare a muscle in a living animal, and irritate it with any agent, it curls up, contracts and is agitated. A detached muscular portion exhibits for some instants the same phenomenon.

Every thing is irritating to the naked muscle, the air, water, neutral salts, the acids, the alkalis, the earths, metals, animal and vegetable substances, &c. The mere contact is sufficient to produce contraction. Yet besides this contact, there is something also which depends upon the nature of the stimuli, and which makes the intensity of the contractions vary. A powder of wood, coal, metal, &c. sprinkled upon the muscles of a frog, produce but slight motions in it; pour on it a neutral salt in powder, the marine salt for example, immediately irregular agitations, and a thousand different oscillations are manifested. Each body is by its nature capable of irritating the muscles differently, as according to individuals, ages, temperaments, seasons, climates, &c. the muscles are capable of answering differently to excitements made upon them.

It is not necessary to irritate the whole of a muscle to produce its contraction; two or three fibres only being pricked bring into action all the others. Often even when we make these experiments on a living animal, the contraction is communicated from one muscle to another. In general I have constantly observed that during life these experiments are less easy, and give results much more various, as we have already stated with regard to animal contractility. Lay bare a muscle, irritate it at many different times; sometimes it does not give the least sign of contractility; sometimes it moves with force; this varies from one instant to another. Whereas if it is upon an animal recently killed that the experiments are made, the results are always nearly the same in a given time, with the difference however of the weakness which the contractions have in proportion to the length of time after death. It never happens that you see a muscle immoveable under stimuli, which is not rare in a living animal. This essential difference which authors have not sufficiently pointed out, and which I have frequently proved upon different animals, arises from this, that during life, the effects of the nervous influence counteract those of the stimuli; for example, if an animal extends with force his thigh by the posterior muscles, we may in vain irritate the anterior ones, we cannot produce flexion by this irritation. The cerebral excitement in the extensors being stronger than the mechanical excitement in the flexors, triumphs. Often when we apply the stimulant, the brain acts with force upon the muscle, the effect is then much superior to the excitement we have applied. We are astonished; but the astonishment ceases, if we recollect that there is a concurrence of two excitements, of that of the external agent and of that of the brain. In general, those who have made experiments, have not paid sufficient attention to this concurrence of the two forces in a living animal.

In order to estimate correctly the sensible organic contractility, it is necessary to destroy the animal contractility. So long as these two clash, interrupt and counterbalance each other, we cannot properly estimate them, and determine what belongs to each and what is common to both. Now we destroy animal contractility in the living subject, by cutting all the nerves of a muscle or an extremity, which then become paralyzed. The brain can no longer act upon them, and the results we obtain from stimuli, belong to the sensible organic contractility.

The duration of this last property, after the experiment I mentioned, proves completely that the nerves are wholly foreign to it, that it resides essentially in the muscular texture, that it is, as Haller said, inherent in it. Thus whilst in the different paralyses the muscles lose the power of obeying the cerebral influence, or rather this influence becomes nothing, they preserve that of contracting in an evident manner when stimulated.

This contraction of the muscles of animal life by stimulants, appears under two very different modes. 1st. The whole of the muscle can contract and shorten so as to approximate the two points of insertion. This happens in general when death is recent, when the muscle is still fully possessed of life. 2d. There are oftentimes numerous oscillations of the fibres; all are in action at the same time; now this action is not a contraction, but a real vibration, a fluttering, which has not a sensible effect upon the whole of the muscle, which not contracting cannot approximate its moveable points. When life is about abandoning entirely the muscle, it is thus that it moves. The diversity of the stimuli occasions also this double mode of contraction. Carry a scalpel over a living muscle, a contraction of the whole will be the consequence; afterwards sprinkle the same muscle with a neutral salt, sometimes there is an analogous contraction; but frequently there are only oscillations, vibrations similar to those of a muscle which life abandons.

During the life of the animal, its sensible organic contractility is rarely in action, because the muscles have not agents that act upon them in a sensible manner at least. Why then is this property so developed in them? I cannot determine.

All the muscles do not possess it to the same degree; the diaphragm and the intercostals are the most irritable; they are also those whose organic contractility is the most permanent after death. Observe that this contrasts, like their susceptibility to receive the nervous influence by the irritation of their nerves, especially of the phrenic, with the little disposition they have to feel, during life, convulsions or paralysis. After them I think that the temporal, the masseter, the buccinator, &c. are the most irritable. There is certainly as it respects irritability a great difference between them and the muscles of the extremities, which are all nearly equally susceptible to the effect of stimulants. Besides, it is only by a great number of experiments that we can establish general data; for nothing is more frequent than to find inequalities between two analogous muscles, and even between the corresponding ones of the two sides of the body.

Sympathies.

The animal muscular system performs a very important part in the sympathies. We see it very frequently agitated with irregular motions in the different affections of our organs, especially in infancy when every lively impression made upon any organ, is almost always followed by spasmodic and convulsive motions in the muscles of animal life. Observe in fact that it is the vital property predominant in this system, that is to say the animal contractility, that is most often brought sympathetically into action in it, by the influences that the organs exert upon each other.

In general it appears that when the animal sensibility is strongly developed in an organ, this system tends immediately to contract. The acute pains that stones occasion in the kidneys, in the ureter and even the urethra, distensions of the ligaments, of the aponeuroses, dentition, surgical operations in which the patient has suffered much, &c. produce very numerous and frequent sympathetic convulsions. I know that there are very severe pains without sympathetic convulsive motions; but it is very rare that you see convulsive motions of this nature, without the organ, from which these sympathetic irradiations go, is very powerfully affected, and the seat of great animal sensibility.

Observe on the contrary that most of the sympathies which develop to a great degree in any part, insensible organic contractility, or sensible organic contractility, are not marked by these acute pains in the affected organ from which the excitement goes; for example, sweats, sympathetic secretions, intestinal and gastric contractions are rarely produced by affections of the character of those from which arise the sympathies of animal contractility.

The brain is always first affected in this last species of sympathies in which the muscles are, as it were, passive, as we have already seen, and in which they are made to obey the impulse they receive. The affected organ acts at first upon the brain, then this re-acts upon the muscles.

Authors have considered sympathies in too loose a manner. Some have admitted, others have rejected the intermediate office of the brain; some have not pronounced upon it. All would be agreed, if instead of attempting to resolve the question in a general manner, they had distinguished the sympathies according to the vital forces, of which they are only aberrations and irregular developments; they would have seen, that in the animal sympathies of contractility, the cerebral action is essential; for we cannot conceive of any contractility of this species, without the double influence, nervous and cerebral, upon the muscles; that on the contrary, in the organic sympathies of contractility, the action of the brain is nothing; the affected organ acts directly and without any thing intermediate upon that which contracts sympathetically. When the heart, the stomach, the intestines, &c. move, when the parotid and other glands increase their action by the sympathetic influence of an affected organ, certainly this organ does not act first upon the brain; for it would then be necessary that this should re-act upon those that contract; now it would not be able to influence them except by the nerves, since it is only by these that it is united to them; but all experiments and all facts prove as we shall see, that the brain has not by this means any influence over the organs with involuntary motions; then the action is direct and there is nothing intermediate. There are sympathetic motions like the natural ones; the sensible and insensible contractilities are constantly brought into action by a direct stimulus applied to the organ, whilst that the animal contractility is never exercised but by the cerebral stimulant, which itself requires a cause, either sympathetic or direct, in order to act upon the muscles.

Next to animal contractility, the sensibility of the same nature is the most often brought sympathetically into action in the animal muscular system. The lassitude, wandering pains, sensation of weight and stretchings that are felt in the limbs in the beginning of many diseases, are phenomena purely sympathetic, in which this property enters into action in the muscles. At advanced periods of many other affections, these sympathetic troubles are also very remarkable, but less in general than at the beginning.

The organic properties are for the most part rarely sympathetically in action in the species of muscles of which we are treating. Besides, if they are so, we can hardly judge of it, because no sign points it out to us. The sweat in the skin, the secreted fluids in the glands, the fluids exhaled upon many of the surfaces, are general results which indicate to us the sympathetic derangements of the organic sensibility and of the insensible contractility of the same species. In the muscles, we have not the same means of knowing these alterations.

Characters of the Vital Properties.

From what we have thus far said, upon the muscular properties and sympathies, it is easily seen that the vital activity must be in general much greater in the muscles than in the organs previously examined in this volume; thus all their affections begin to take a peculiar character that distinguishes them from those of these organs; they are much more prompt and rapid. Yet let us remark that all the alterations of function which they exhibit, cannot assist us in estimating this vital activity. In fact, many of these alterations do not reside essentially in the muscular texture, their cause is not there; such are for example all the convulsive motions in which, as we have seen, the muscles act by obeying, but have not the principle of action in them. They are then the indices of cerebral alterations; thus the arteries, which exhibit such numerous varieties in the state of the pulse, are as it were only passive, and serve most frequently merely to indicate the state of the heart by their motion, whilst the veins, which have not at the origin of their circulation an analogous agent of impulse, very rarely exhibit varieties, though however their texture may have as great vital forces, and its life be as active or more so, than that of the arteries.

One proof that the texture of the muscle is less often altered than it at first seems to be in considering the frequency of the affections of these organs, is the infrequency of their organic lesions. These lesions are even less common in them than in the bones. We do not see in them those schirri, swellings, changes of texture in a word, which are so commonly met with in the other organs. Among the great number of subjects that I have had occasion to dissect or to have dissected, I do not recollect to have seen in the muscles of animal life other alterations than those of their cohesion, their density and their colour. It is a phenomenon that approximates them to those of organic life, in which we rarely meet with changes of texture, as the heart, the stomach, &c. are examples.

The muscular texture of animal life rarely suppurates; thus but little is known of its mode of suppuration. In general, it appears that inflammation terminates in it almost always by resolution. Induration, gangrene and suppuration, three terminations that this affection often makes in the other parts, are unknown to this in the greatest number of cases.

ARTICLE FOURTH.

PHENOMENA OF THE ACTION OF THE MUSCULAR SYSTEM OF ANIMAL LIFE.

Thus far we have spoken of muscular mobility, abstractedly from the phenomena that it exhibits in the muscles, when it is in exercise in them. These phenomena are now to be considered. They relate especially to contraction, which is the essentially active state of the muscle, relaxation being a state purely passive. We shall easily understand the phenomena of this, when those of the other of which they are the reverse are known to us.

I. Force of the Muscular Contraction.