52 The Feeding of Animals 



sues of plants and animals. The basic substance of the 

 active cell is protoplasm, a complex nitrogenous body, 

 which Huxley called "the physical basis of life." Around 

 this primal substance seem to center all vital activities, 

 especially the transformation of the raw materials of the 

 inorganic world into the organized structures of life. 



(2) These compounds are structurally essential to 

 the growth of living tissues and to the formation of 

 milk. The significance of this fact is intensified by 

 their paucity in many of the feeding stuffs that are 

 ordinarily produced on the farm. 



(3) Nitrogen combinations suitable for use as plant 

 and animal food have reached a position of great com- 

 mercial importance. They are the most costly of all 

 the plant-building materials, the significance of which 

 is intensified by their scarcity in the soil in useful 

 forms, and by their easy passage bej^ond reach either 

 through chemical changes which liberate the nitrogen, 

 or through leaching from the soil. Nitrogenous feed- 

 ing stuffs also bear relatively high market prices. 



PROTEIN 



For the sake of brevity and convenience, the nitro- 

 gen compounds of cattle foods, both vegetable and 

 animal, are designated as a class by the single term 

 protein. When, therefore, it is stated that a feeding, 

 stuff contains a certain percentage of protein, refer- 

 ence is made to the total mass of nitrogen compounds 

 present, which may be many in number and of greatly 

 differing characteristics. 



