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 ct, 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. 



Q 2 



