316 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



by too constant use. The more violent the action, the longer will be the period 

 of subsequent repose required for the reparation of the tissue : and the longest 

 time will of course be requisite, when (as sometimes occurs) the contractility of 

 the muscle is so completely exhausted by excessive stimulation that no new 

 manifestation of it can be excited. Nevertheless it is certain, that there must 

 be a provision in some Muscles, 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 unceasing action during the whole of life, be kept in a 

 state fit for the discharge of their functions. 



313. But, on the other hand, the Muscular tissue, like all the softer and 

 more decomposable portions of the organized fabric, has a limited term of exist- 

 ence ( 114) ; and hence, even if its contractility be not called into exercise, it 

 undergoes a gradual disintegration, so soon as all the nutritive changes of which 

 its component cells are susceptible, have been completed. This change seems 

 to be a necessary consequence of the high temperature of the bodies of warm- 

 blooded animals ; for it does not occur with nearly the same rapidity in cold- 

 blooded Animals, nor in the hybernating condition of certain warm-blooded 

 Mammalia; indeed, when the temperature of the body is reduced to within a 

 few degrees of the freezing point, no chemical change seems possible in muscle, 

 its spontaneous decay, and its vital activity, being alike checked. Now when 

 a Muscle or set of Muscles, in a warm-blooded animal, is reduced to a state of 

 prolonged inactivity, from whatever cause, its supply of blood is diminished, 

 and its spontaneous decay is not compensated by an equally active renewal ; so 

 that, in time, the characters of the structure are changed, and its distinguish- 

 ing properties are no longer presented. Thus it was found by Dr. John Reid, 1 

 that, in a rabbit, a portion of whose sciatic nerve had been removed on one side, 

 the muscles of that leg were but very feebly excited to contraction by Gal- 

 vanism, after the lapse of seven weeks. The change in their nutrition was 

 evident to the eye, and was made equally apparent by the balance. The mus- 

 cles of the paralyzed limb were much smaller, paler, and softer, than the cor- 

 responding muscles of the opposite leg ; and they scarcely weighed more than 

 half being only 170 grains, whilst the others were 327 grains. It was found 

 also, that a perceptible difference existed in the size of the bones of the leg, 

 even after so short an interval had elapsed : the tibia and fibula of the para- 

 lyzed limb weighing only 81 grains, whilst those of the sound limb weighed 89 

 grains. On examining the muscular fibres with the microscope, it was found 

 that those of the paralyzed leg were considerably smaller than those of the 

 sound limb, and presented a somewhat shrivelled appearance ; and that the 

 longitudinal and transverse striae were much less distinct. So in persons whose 

 lower extremities have been long disused, the muscles first become pale and 

 flabby ; their bulk gradually diminishes ; their contractile force progressively 

 decreases, and at last departs almost entirely; and their proper structure is 

 replaced by a deposit of fat, intermixed with ordinary fibrous tissue, in which 

 few or no characteristically-striated muscular fibres can be detected. But mus- 

 cles that have for some time remained in this condition may be gradually 

 brought back to their original state by exercise, provided that the feeblest 

 contractility remains ; for every action which they can be made to perform, 

 determines an augmented flow of blood through the tissue, and gives rise to an 

 improvement in its nutrition, which in its turn increases its contractility, and 

 renders it capable of more vigorous action. This principle is of great import- 

 ance in the treatment of various forms of paralysis (especially the hysterical), 

 in which the muscles are thrown out of use by the suspension of the functional 



1 "Edinburgh Monthly Journal of Medical Science," May, 1841 ; and "Physiological, 

 Anatomical, and Pathological Researches," p. 10. 



