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._