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CHAPTER X. 



Circulation. 



§ 1. Diffused Circulation. 



Animal life, implying mutual actions and reactions be- 

 tween the solids and fluids of the body, requires for its 

 maintenance the perpetual transfer of nutritive juices from 

 one part to another, corresponding in its activity to the ex- 

 tent of the changes which are continually taking place in 

 the organized system. For this purpose we almost con- 

 stantly find that a circulatory motion of the nutrient fluids 

 is established; and the function which conducts and regu- 

 lates their movements is emphatically denominated the Cir- 

 culation. Several objects of great importance are answered 

 by this function; for in the first place, it is through the cir- 

 culation that every organ is supplied wiih the nutritive 

 particles necessary for its development, its growth and the 

 maintenance of its healthy condition; and that the glands, in 

 particular, as well as the other secreting organs, arc fur- 

 nished with the materials they require for the elaboration of 

 the products, which it is their peculiar ofiice to prepare. A 

 second essential object of the circulation, is to transmit the 

 nutritive juices to certain organs, where they are to be sub- 

 jected to the salutary influence of the oxygen of the atmo- 

 sphere; a process which in all warm-blooded animals, com- 

 bined with the rapid and extensive distribution of the blood, 

 difl'uses and maintains throughout the system the high tem- 

 perature required by the greater energy of their functions. 

 Hence it necessarily follows that the particular mode in 

 which the circulation is conducted in each respective tribe, 



