282 



OF MUSCULAR CONTRACTILITY. 



opinion, that every act of Muscular contraction necessarily involves the death 

 and disintegration of a certain amount of Muscular Tissue ( 77) ; and it has 

 been recently argued by Liebig, that this disintegration, resulting from the 

 action of Oxygen upon the elements of which the tissue is composed, is the 

 real source of the mechanical power ; by setting at liberty (so to speak) the 

 Vital Force, which was previously employed, in a latent manner, in holding 

 together the components of the structure. Certain it is, that the amount of 

 Muscular power exercised by an animal, bears a very close correspondence 

 (other things being equal), on the one hand to the measure of oxygen intro- 

 duced into the system by the lungs, and on the other to the amount of those 

 excretions, which seem especially produced by this metamorphosis : and this 

 is true, as a general fact, whether we compare together different animals, or 

 different states of the same animal (See Chap. vm. Sect. i). 



378. The effects of stimuli locally applied to portions of the Muscles of 

 Animal Life, are very different from those which result from their application 

 to the muscles of Organic life. If, for example, we irritate mechanically a 

 portion of the Biceps, the fasiculus of fibres which is touched will contract, 

 but the surrounding parts will be unaffected, and the contracted fasciculus 

 will soon relax ; in fact, the only way to call the whole muscle into contrac- 

 tion at once, is to stimulate it through its nerves. On the other hand, if we 

 apply a similar irritation to the intestinal canal, when in a state of equal con- 

 tractility, the fasciculus which is stimulated shortens in a much greater 

 degree ; and propagates its action in a wave-like manner to other bundles of 

 fibres; so that successive contractions and relaxations may be produced, 

 through a considerable part of the canal, by a single prick with the point of a 

 scalpel ; but the contractions into which these same fibres are thrown, by irri- 

 tating their nerves, are for the most part feeble and undecided ( 200). It is, 

 indeed, a curious fact, corroborative of what has been just said of the influence 

 of narcotics, that the ganglionic nerves lose their power of exciting these 

 muscles to contraction, when themselves irritated, much sooner than the 

 muscles lose their power of contraction, when directly stimulated. 



379. There can be no doubt that it is through the motor or efferent nerves, 

 that contraction is ordinarily excited in the muscles of the first class, in the 

 living body ; and these nerves may, as formerly shown, convey the influence 

 of volition, of emotional or instinctive operations of mind, or of the reflex 

 action of the Spinal Cord. As the effect produced upon the muscle is in all 

 instances similar, there can be little doubt that the stimulus actually commu- 



Fig. 71. 



Form of the terminating loops of the Nerves in the Muscles. After Burdach. 



