328 PRODUCTIVE FARMING 



Essentials in Animal Feeds. As the animal body con- 

 sists of several classes of substances, it demands similar 

 classes from the feeds consumed. The substances in animal 

 feeds are: (1) Protein, (2) carbohydrates, (3) fats, (4) mineral 

 salts. 



Protein. The protein of a feed includes vegetable albu- 

 men, fibrin, and other substances similar to the protein of 

 the animal body. The term albumenoids was formerly used 

 to designate this class of substances when contained in feed 

 or in animal tissues. 



The different kinds of protein substances vary somewhat 

 in their composition. They are all rich in nitrogen, and are 

 quite uniform in their value in feeds. They are the most 

 important of the compounds in feed, and are indispensable, 

 as they are the sole direct source of the protein in the bodies 

 of all domestic animals. The chief forms in which protein 

 is found in the animal's body are: albumen, fibrin, and casein. 

 These differ widely in appearance but agree in containing 

 about the same percentage of nitrogen. Gluten is abundant 

 in wheat. Albumen is well represented by the white of an 

 egg. Fibrin is seen in the white solid of coagulated blood 

 remaining after the red color is washed out. Casein is the 

 basis of cheese. 



EXERCISE. Protein in Wheat. Make some stiff dough 

 of wheat flour. Wash the dough in cold water to remove 

 the starch. The remainder will become very elastic. It is 

 made up chiefly of that kind of protein called gluten. The 

 "gum" formed from chewing wheat is also chiefly gluten. 



EXERCISE. Study of Protein. Examine some of the 

 other substances mentioned, and let pupils become familiar 

 with the different forms of protein. Have present the white 

 of egg, both raw and cooked. American cheese or cottage 

 cheese, or both, may be put into small bottles with a weak 

 solution of formalin to preserve them for future use in 

 illustrating that form of protein called casein. 



