144 The Feeding of Animals 



its constituents are found members of all the classes 

 of compounds that are important in this connection, — 

 ash, protein, carbohj'drates and fats. The proportion 

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

 common salt, and the remainder consisting of phos- 

 phoric acid, lime and other important mineral com- 

 pounds. The solid matter of the plasma is rich in 

 albuminoids, including the fibrinogen which is the 

 mother substance of fibrin and several albumins and 

 globulins. These proteids make up about 80 per 

 cent of the total dry substance of plasma. Sugar and 

 fats are also present, their proportions varying 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. 



THE HEART 



In quantity, the blood is from 3 to 4 per cent of 

 the total weight of the live animal. It is contained in 

 the heart and in two sets of vessels, one set called the 

 arteries leading 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 these vessels the blood is moving in 

 a constant stream, which we call the circulation. It 

 does not move of itself, but is forced along by a very 

 powerful pump, the heart. This is a highly muscular 

 organ divided into four chambers, which are separated 

 by valves and partitions, the two upper chambers be- 



