We cannot increase, by constant exercise, the nutrition of the organic muscles. Aliments taken beyond measure, making the stomach frequently contract, weaken it instead of developing its fibres more, as happens from constant exercise given to a superior or inferior extremity. The bladder incessantly in action in some cases of incontinence, is thus gradually weakened and loses its energy. We might say that these two systems were in this respect in an inverse order. It appears that the nutrition of the organic muscles, like that of the others, is subject to frequent variations; that at some periods they are more developed and less so at others. Diseases have a great influence upon this phenomenon, which proves, like the softening of the bones and their return to the natural state, the constant composition and decomposition of which these organs are the seat. We find in the dissecting rooms many differences in different subjects, as it respects the colour, density and cohesion of the muscles. Now what many exhibit then at once, the same individual often experiences successively; the same man no doubt has, according to the different influences to which he is exposed, his heart red, dense, large and well nourished at one period of life, and feeble, pale and small at another; for the internal organs experience the same alterations as the exterior. Now we know that the external appearance often changes during life. IV. _State of the Organic Muscular System in Old Age._ As we advance in age, the muscular system of which we are treating becomes weak like all the others; yet its action is more durable; it survives, if we may so say, that of the other. When the old man, almost immoveable, crawls about but slowly and with pain, his pulse, digestion, &c. have vigour still. This difference of the two systems is so much the more remarkable, as the time of activity of the second is almost by half less than that of the first; sleep cuts off in fact almost half of the duration of the voluntary motions, whilst it leaves the involuntary wholly untouched. This phenomenon of the organic muscles as it were surviving the voluntary in the last periods of life, is derived on a great scale from the same principle from which arises on a small one the lassitude which follows the contraction in an insulated motion. A less durable motion is necessary to fatigue the voluntary muscles, than to fatigue the involuntary; the stomach empty remains for a long time contracted upon itself without producing any painful sensation, whilst if we hold a body strongly grasped between our fingers for a quarter of an hour, all the flexors are soon painfully affected. After a convulsion of half an hour, in which all the locomotive muscles have been stiff, the whole body is broken, as it is called; it cannot admit of any motion; whilst after a paroxysm of fever of six or eight hours in which the pulse has been violently agitated, the heart often preserves the natural type of its