MOVEMENTS PRODUCED BY MUSCULAR CONTRACTION. 445 
find a peculiar tissue, the Muscular (§§ 55—59), distin- 
i 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 Crganic life merely, are rendered subservient to the Will, 
and 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. 
_ 680. The peculiar contractility of muscular fibre may be 
called into action by various means. As in certain vegetable 
tissues (Vecet. Pays. § 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 
