Chap, xiv.] LYMPHATIC CIRCULATION. 227 



movement of translation has only two possible causes, the 

 pression exercised by the absorption itself in the fine canalicules, 

 the vis & tergo, and, as an auxiliary force, the contraction of the 

 walls ; that is to say, the principal agents of circulation in the 

 veins. We may therefore, by analogy, conclude that in the 

 sanguineous circulatory system the heart is simply a reinforcing 

 organ, and that a very great part of the propulsive labour is 

 accomplished by the vessels themselves. 



q2 



