140 THE FEEDING OF ANIMALS 



for use. When thus charged, it is known as oxyhemo- 

 globin. Because of this function of their most prominent 

 constituent, blood corpuscles become the carriers of 

 oxygen to all parts of the body. The blood corpuscles 

 are also concerned in gathering up one of the waste 

 products of metabolism, viz., carbon dioxid, and convey- 

 ing it to the point where it may be thrown off from the 

 body. (See Par. 77.) 



201. The blood plasma. — ^The plasma is a liquid 

 having a very complex composition. It is about nine- 

 tenths water, so that it easily holds in solution whatever 

 soluble nutrients are discharged into it from the alimen- 

 tary canal. Among its constituents are found members of 

 all the classes of compounds that are important in this 

 connection — ash, protein, carbohydrates, and fats. The 

 proportion of ash is about 1 per cent, three-fourths of it 

 being common salt, and the remainder consisting of 

 phosphoric acid, lime, and other important mineral com- 

 poimds. The solid matter of the plasma is rich in pro- 

 teins, including the fibrinogen which is the mother sub- 

 stance of fibrin and several albumins and globulins. 

 These proteins make up about 80 per cent of the total 

 dry substance of plasma. Sugar and fats are also present, 

 their proportions undoubtedly varying somewhat with 

 the extent to which they are being absorbed from the 

 digestion of food. It is evident that the blood is charged 

 with those materials which we recognize as necessary to 

 the construction and maintenance of the animal body. 



202. The heart. — ^The blood is contained in the heart 

 and in two sets of vessels, one set called the arteries lead- 

 ing from the heart by various ramifications to all parts 

 of the body, and the other set called the veins, leading 

 from all parts of the body back to the heart. Through 



