THE STRUCTURE OF ANIMALS. 157 



are floating a large number of small disc-shaped particles, 

 which are called corpuscles. Most of these are red, and thereby 

 give a red color to the blood. Some are white corpuscles. It 

 is by means of these corpuscles that much of the material is 

 carried through the system. For instance, in the lungs they 

 take up a load of oxygen and carry it to all parts of the body 

 and bring back a load of carbonic acid gas to be breathed 

 out from the lungs. In the plasma is contained much of the 

 material that goes to build up bone and flesh. We have seen 

 that when the albumen of milk or white of egg is heated it 

 becomes insoluble, or is clotted. When acids are added to 

 milk, the casein becomes clotted. In plasma there is a similar 

 nitrogenous substance, fibrin, which is clotted by the action of 

 the air. When blood flows from a cut, therefore, the clotted 

 fibrin and the corpuscles that are entangled in it form a cover- 

 ing for the wound otherwise the animal would bleed to death. 

 When a clot forms inside of the body, circulation stops at that 

 point, and death frequently results. In a man the blood forms 

 about one-thirteenth of his entire weight. 



CONCLUSION. Apart from the water of the body, the various 

 digestive liquids and agents, and the blood, we have, then, 

 three classes of compounds in the animal body the bones ; 

 the fat ; and the muscles, the various organs, lean flesh, hair, 

 hoofs, and horns. The bones, as we have already stated, are 

 largely made up of ash or mineral matter ; the fat contains 

 three chemical elements carbon, hydrogen, and oxygen; the 

 third, or muscle class, is made up of five elements carbon, 

 hydrogen, oxygen, nitrogen, and sulphur. To show in what 

 proportion these are contained in an animal's body, we give 

 one example. The body of a half-fat ox, after the removal of 

 the stomach and intestines, will contain in every 100 pounds 

 the following : Water, 56 pounds ; flesh and muscle material, 

 1 8 pounds; fat, 21 pounds; bone material, 5 pounds. 



