OF VITAL MOTION. d5 



faulty, then the vessels are shrunken and collapsed. 

 In so far, therefore, as concerns the muscular tissue 

 present in the coats of these vessels, it is evident that 

 the state of contraction is not induced by the stimu- 

 lant properties of the blood. 



In nature and office the bloodvessel is very inti- 

 mately related to the alimentary canal ; and hence it 

 may be expected that the influence of the food and the 

 blood, upon the passages with which they are severally 

 related, will present many points of correspondence 

 and analogy. And such indeed is the fact. 



The food is said to stimulate contraction in the 

 coats of the alimentary canal; but let us examine 

 what is involved in this supposition. If a morsel 

 acts in this manner, how is it, we may ask, that the 

 act of contraction does not prevent its admission into 

 the gullet ; or if by chance it be admitted, how is it that 

 it is not immovably fixed there? There is no phy- 

 sical necessity that the muscular acts should follow in 

 a certain and definite order ; for, in the ordinary peri- 

 staltic movements, an impulse which passed in one 

 direction at first may the next moment be entirely 

 reversed. Again ; in the movements of the guUet in 

 the cow, or in any other ruminant animal, we have 

 a simple proof of this fact ; for, during the process of 

 rumination, the morsel is seen to ascend and descend 

 alternately, where the gullet lies superficially at the 

 side of the neck. There is no reason, therefore, so 



F 



