OF VITAL MOTION. 35 



powers of the latex vessels: and in the higher 

 animal when the circulation flags and the heart beats 

 faintly and irregularly, it is interesting to observe 

 that the blood no longer moves in a continuous stream 

 in one direction in the capillaries, but oscillates irre- 

 gularly to and from certain points, in such a manner 

 as to show a tendency to the revival of those nume- 

 rous centres of action, which had been absorbed and 

 superseded by the heart. 



2. Of intra-organic force as the agent in the 

 capillary movements. 



In vegetables the vascular movements are mainly 

 dependent upon the agency of extrinsic force, but in 

 animals the case is altered, and the internal or organic 

 powers gain the ascendancy, except in the hyber- 

 nating class, where perhaps the influence of the two 

 is nearly balanced. 



The internal or organic force may be divided into 

 two principal forms, and each of these will demand 

 separate consideration. The first is connected with 

 the mysterious operations of the nervous system ; and 

 the other, which is less vague and indefinite in its 

 character, in the expression of the several molecular 

 changes which constitute the functions of nutrition, 

 respiration, and secretion. 



d2 



