DISINTEGRATION AND NUTRITION OF MUSCLE. 445 



Muscle, which is of a nature destructive to its integrity as an organized tissue. 

 For, in the first place, the researches of Helmholtz, formerly referred to 

 ( 238, 6), indicate such a change, from the comparative results of Chemical 

 analysis of the muscle, before and after the violent excitement of its contrac- 

 tility. But it is still more decidedly shown, by the increase in the excretions, 

 which is consequent upon Muscular activity; and especially by the augmenta- 

 tion of the Carbonic acid set free from the respiratory organs, and by that of 

 the Urea set free from the kidneys. The amount of the latter, indeed, may be 

 regarded, cseteris paribus, as an approximative indication of the quantity of 

 Muscular tissue which has undergone disintegration ; being increased or 

 diminished, in precise proportion to the degree of exertion to which the 

 Muscular system has been subjected. It cannot but be regarded as a probable 

 inference from these facts, that the development of the Contractile force is in 

 some way dependent upon the Chemical change, which seems to be so essen- 

 tial a condition of it; just as the development of the Electric force of the 

 Galvanic battery is dependent upon the new chemical arrangements, which 

 take place between the bodies brought to act upon one another in its trough. 



587. The frequently-renewed exercise of Muscles, by producing a deter- 

 mination of blood towards them, occasions an increase in their nutrition ; so 

 that a larger amount of new tissue becomes developed, and the muscles are 

 increased in size and vigour. This is true, not only of the whole Muscular 

 system when equally exercised; but also of any particular set of muscles, 

 which is more exercised than another. Of the former we have examples in 

 those who practise a system of Gymnastics adapted to call the various mus- 

 cles alike into play ; and of the latter, in the limbs of individuals who follow 

 any calling, that habitually requires the exertion of either pair, to the partial 

 exclusion of the other, as the arms of the Smith, or the legs of the Opera- 

 dancer. But this increased nutrition cannot take place, unless an adequate 

 supply of food be afforded ; and if the amount of nutritive material be insuffi- 

 cient, the result will be a progressive diminution in the size and power of the 

 muscles ; which will manifest itself the more rapidly, as the amount of exer- 

 tion, and consequently the degree of waste, are greater. Nor can it be effected, 

 if the exercise be too constant ; for it is during the intervals of repose that 

 the reparation of the muscular tissue occurs; and the Muscular system, like 

 the Nervous ( 294), may be worn out by too constant use. The more violent 

 the action, the longer is the period of subsequent repose, which is required for 

 the reparation of the tissue : and the longest will, of course, be requisite, when 

 (as sometimes occurs) the contractility of the muscle is so completely ex- 

 hausted by excessive stimulation, that no new manifestation of it can be ex- 

 cited. Nevertheless it is certain, that there must be a provision in some Mus- 

 cles, for the continuance of their nutrition during their state of activity; for in 

 no other way could the Heart and Respiratory Muscles, which are in unceas- 

 ing action during the whole of life, be kept in a state fit for the discharge of 

 their functions. 



588. On the other hand, Muscular Irritability, like the vital properties of 

 other parts, is diminished by want of action; and in this, as in other cases, it 

 is quite clear that the cause of its loss is to be found in the alteration of the 

 nutritive processes, which is the uniform result of the cessation of the usual 

 operations of any part. The Muscular tissue, like all other soft organized 

 substances, has a constant tendency to spontaneous disintegration, especially 

 at the high temperature of the body in warm-blooded animals ; and it is con- 

 sequently subject to a slow and regular waste, quite irrespectively of that pro- 

 duced by its vital activity.* Now when a Muscle or set of Muscles, in a 



This does not occur with nearly the same rapidity in cold-blooded Animals, nor in the 

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