CIRCULATION OF TPIE BLOOD. 399 



blood again charged with oxygen, and becomes of a bright 

 scarlet color. If the carbonic acid, which the blood takes up 

 as it circulates through the body, were not thrown off, death 

 would soon take place. Neither could life continue for more 

 than a few seconds if oxygen were not mixed with the blood in 

 the lungs. Now, oxygen is one of the two gases which are 

 mixed together to form the air which all animals breathe. It 

 is called vital air. If the air which the animal breathes is 

 not fresh and pure, there will not be the proper quantity of 

 oxygen taken into the lungs, and the animal must suffer from 

 its want. Hence the importance of keeping stables clean and 

 supplied with fresh air. The blood contains every thing neces- 

 sary for repairing the worn-out j^arts of the body, and which, 

 as it flows through the system, are deposited, or left, exactly 

 where they are needed. But, it may be asked, where does the 

 blood get these particles fit for supplying this waste? It gets 

 part of them from the food ; after it is digested in the stomach, 

 and as it passes through the bowels, it is absorbed into 

 the veins. Also, the w^orn-out particles of the system are 

 taken up by a set of vessels called lacteals, and by them car- 

 ried back into the blood, and again fitted for the repair of the 

 body. But those parts that have become utterly unfit for any 

 purpose are thrown ofP from the body by the bowels, skin, lungs, 

 or kidneys, in the form of dung, sweat, or perspiration, gases, 

 and urine, or water. 



The quantity of blood in the animal is generally about one- 

 fifth of his weight. The blood contains several different parts, 

 of which water is the largest. But the most important are the 

 red corpuscles, albumen, and fibrine. The white of an egg is 

 albumen, but that in the blood is thinner. Fibrine is a white, 

 stringy substance. It may be obtained by taking a switch and 

 stirring a clot of blood, and then washing it. It is, in its nat- 

 ural state, a liquid, but as the blood cools, it becomes solid little 

 fibers, or threads, which cause the blood to clot. 



The heat of the animal body is mainly dependent on the 



