204 THE VITAL FUNCTIONS. 



of an arrow ; and many presenting a triangular, a 

 quadrilateral, or other polygonal outline. In many 

 of the Invertebrata these corpuscles have a very 

 irregular shape ; often exhibiting a tuberculated 

 surface, like a raspberry. In the Annelida, they 

 are generally circular, but much larger than in 

 man. 



Chapter X. 



CIRCULATION. 



§ 1. General Plans of Circulation. 



Animal life, implying mutual actions and reac- 

 tions between the solids and fluids of the body, 

 requires for its maintenance the perpetual transfer 

 of nutritive juices from one part to another, corre- 

 sponding in activity to the extent of the changes 

 which are continually taking place in the organized 

 system. For this purpose we almost constantly 

 find that a circulatory motion of the nutrient fluids 

 is established ; and the function which conducts 

 and regulates their movements is emphatically 

 denominated the Circulation. Several objects of 

 great importance are answered by this function ; 

 for, in the first place, it is through the circulation 

 that every organ is supplied with the nutritive par- 

 ticles necessary for its developement, its growth, 

 and its maintenance in a healthy condition ; and 

 that the glands, in particular, as w^ell as the other 

 secreting organs, are furnished with the materials 

 they require for the elaboration of the products. 



