446 OF MUSCULAR CONTRACTION. 



warm-blood animal, is reduced to a state of prolonged inactivity, from what- 

 ever 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 distinguishing properties are no longer 

 presented. Thus 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 altogether ; 

 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. 



589. The continual and evident influence of the Nervous System upon 

 Muscular Irritability, has led many Physiologists to the belief, that the latter 

 is dependent upon the agency of the former. Two views upon this question 

 have been commonly taught, to both of which it seems necessary to devote a 

 brief consideration. The first of these is, that Muscular Irritability is derived 

 from some influence or energy communicated from the Brain or Spinal Cord. 



a. This opinion is evidently analogous to that which attributes the vital properties of 

 other parts to the Nervous System alone ; and it is open to the same objection, in laming 

 which has been applied to the latter, the improbability that anyone of the solid textures of the 

 living body, should have for its office to give to any other the power of performing any vital 

 action. Moreover it is inconsistent with the fact that, in Vegetables, tissues endowed with 

 a high degree of contractility exist, and manifest their property 'when a stimulus is directly 

 applied to themselves; which, nevertheless, can have no dependence whatever upon a 

 nervous system. In the lower classes of Animals, too, there is good reason to believe, that 

 the property is much more universally diffused through their tissues, than nervous agency 

 can be. Again, the action of the heart may be kept up, in the highest Animals, by taking 

 care that the current of the circulation be not interrupted, for a long time after the removal 

 of the brain and spinal cord ; it may even continue when completely separated from the 

 body, which shows that the great centres of the ganglionic system cannot supply any influ- 

 ence necessary to it; and there are many instances, in which the human fcetus has come to 

 its full size, so that its heart must have regularly acted, without the existence of a brain or 

 spinal cord. Further, the irritability of muscles of the first class continues for a long time 

 after their nerves are divided, and may be called into action by stimuli directly applied to 

 the parts themselves, or to their nerves below the section, so long as their nutrition is unim- 

 paired. 



6. The loss of the irritability of Muscles, within a few weeks after the section of their 

 nerves, on which great stress has been laid by Miiller in support of a modified form of the 

 above doctrine, (it being maintained by this distinguished physiologist, that, if muscular irri- 

 tability is not dependent on the Brain and Spinal Cord, they supply some influence essential 

 to its exercise,) is clearly due to the alteration in their nutrition', consequent upon their dis- 

 use. This has been recently proved to demonstration, by the very ingenious experiments of 

 Dr. J. Reid.* "The spinal nerves were cut across, as they lie in the lower part of the spinal 

 canal, in four frogs; and both posterior extremities were thus insulated from their nervous 

 connections with the spinal cord. The muscles of one of the paralyzed limbs were daily 

 exercised by a weak galvanic battery ; while those of the other limb were allowed to remain 

 quiescent. This was continued for two months; and at the end of that time, the muscles of 

 the exercised limb retained their original size and firmness and contracted vigorously, while 

 those of the quiescent limb had shrunk to at least one-half of their former bulk, and pre- 

 sented a marked contrast with those of the exercised limb. The muscles of the quiescent 

 limb still retained their contractility, even at the end of two months; but there can be little 

 doubt that, from their imperfect nutrition, and the progressing changes in their physical 

 structure, this would in no long time have disappeared, had circumstances permitted the 

 prolongation of the experiment."! This experiment satisfactorily explains the fact ob- 



hybernating condition of certain warm-blooded Mammalia; indeed, when the temperature 

 i ihc luidy is ivdiirrd 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. 

 * Kdinliiirgh Monthly .Ionni;il of .Medical Science, May, 1841. 



~(~ A fact of an exactly parallel character has fallen under the Author's observation, in a 



of Hysteric Paraplegia, in which one leg was occasionally affected with severe cramps. 



The muscles of this leg suffered much less diminution of size and firmness, than those of 



