MOVEMENTS PRODUCED BY MUSCULAR CONTRACTION. 445 



find a peculiar tissue, the Muscular ( 55 59), distin- 

 guished from the rest ; in which the general contractility of 

 the body becomes, as it were, concentrated. In proportion to 

 the development and complexity of this muscular apparatus, 

 it supersedes, the more feeble contractility diffused through 

 the fabric of the lower tribes. It now, moreover, becomes in 

 great degree subjected to the Nervous System ; by which all 

 those parts of it which are not connected with the functions 

 of Organic life merely, are rendered subservient to the Will, 

 :md thus become its instruments in determining the place 

 and the various actions of the body. Still we find that the 

 ordinary actions of those portions of the muscular apparatus 

 which are most immediately subservient to the functions of 

 organic life, are essentially independent of nervous influence, 

 and are very little under its control ; as we see in the case of 

 the alternate contraction and relaxation of the heart, and the 

 peristaltic movements of the alimentary canal. 



580. The peculiar contractility of muscular fibre may be 

 called into action by various means. As in certain vegetable 

 tissues (VEGET. PHYS. 390), contraction may be excited by 

 a mechanical stimulus directly applied to the muscle itself 

 Thus, if the heart of an animal recently killed be touched 

 with a pointed instrument, it will contract and then dilate, as 

 if performing its ordinary action ; and this may be repeated 

 several times. In the same manner, if the walls of the intes- 

 tinal canal be pricked or pinched, they will re-commence and 

 continue for a short time their peristaltic movement. And if 

 any part of an ordinary muscle be irritated in the same 

 manner, that particular bundle will contract, but the rest will 

 not be affected. Now these actions are analogous to those 

 performed by the Sensitive Plant, Venus' s Fly-trap, and many 

 other plants, some part of whose tissues contracts in like 

 manner when an irritation is applied to it, causing it may 

 be extensive and important motions. It appears to be in 

 this manner that the contractions of the heart, and of the 

 alimentary tube from the stomach to the rectum, are ordinarily 

 excited in the living body. 



581. But there must be some other cause for the con- 

 tinuance of the rhythmical movements of the heart, as well as 

 of some other organs; for the heart of many cold-blooded 

 animals will continue to contract and dilate many hours after 



