USES OF THE BLOOD. 95 



the waste substance of the tissues, but also such matters 

 as, having been taken with food and drink, may have been 

 absorbed from the digestive canal, and have been sub- 

 sequently found unfit to remain in the circulating current. 

 And, 3rdly,_ 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 appro- 

 priate 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 observed, 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 excreting organs specially present 

 for such a purpose. 



Uses of the Blood. 



The purposes of the blood, thus developed and main- 

 tained, appear, in the perfect state, to be these; 1st, to be 

 a source whence the various parts of the body may abstract 

 the materials necessary for their nutrition and mainte- 

 nance; and whence the secreting organs may take the 

 materials for their various secretions; 2nd, 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 mani- 

 fested by them in various forms as vital power ; ^rd, 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 ; ^.th, to bring from all parts refuse 

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

 charged ; 5^/1, 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 



