USES OF THE BLOOD. 85 



including in this term not only the waste substance of the 

 tissues, but also such matters as, having been taken with food 

 arid drink, may have been absorbed from the digestive canal, 

 and have been subsequently found unfit to remain in the cir- 

 culating current. And, 3dly, the precise constitution of the 

 blood is adjusted by the balance of the nutritive processes for 

 maintaining the several tissues^so that none of the materials 

 appropriate for the maintenance of any part may remain in 

 excess in the blood. Each part, by taking from the blood the 

 materials it requires for its maintenance, is, as has been ob- 

 served, in the relation of an excretory organ to all the rest; 

 inasmuch as by abstracting the matters proper for its nutrition, 

 it prevents excess of such matters as effectually as if they were 

 separated from the blood and cast out altogether by the ex- 

 creting organs specially present for such a purpose. 



Uses of the Blood. 



The purposes of the blood, thus developed and maintained, 

 appear, in the perfect state, to be these : 1st, to be a source 

 whence the various parts of the body may abstract the ma- 

 terials necessary for their nutrition and maintenance ; and 

 whence the secreting organs may take the materials for their 

 various secretions ; 2d, to be a constantly replenished store- 

 house of latent chemical force, which in its expenditure will 

 maintain the heat of the body, or be transformed by the living 

 tissues, and manifested by them in various forms as vital power ; 

 3d, to convey oxygen to the several tissues which may need it, 

 either for the discharge of their functions, or for combination 

 with their refuse matter ; 4th, to bring from all parts refuse 

 matters, and convey them to places whence they may be dis- 

 charged ; 5th, to warm and moisten all parts of the body. 



Uses of the various Constituents of the Blood. 



Regarding the uses of the various constituents of the blood, 

 it may be said that the matter almost resolves itself into an 

 analysis of the different parts of the body, and of the food and 

 drink which are taken for their nutrition, with a subsequent 

 consideration of how far any given constituent of the blood 

 may be supposed to be on its way to the living tissues, to be 

 incorporated with and nourish them ; or, having fulfilled its 

 purpose, to be on its way, in a more or less changed condition, 

 to the excretory organs to be cast out. It must be remem- 

 bered, however, that the blood contains also matters which 

 serve by their combustion to produce heat, and, again, others 

 which possibly subserve pnly a mechanical, although most im- 



