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.