158 THE FEEDING OF ANIMALS 



cium phosphate. It seems clear, however, that growth 

 can be secured where only inorganic phosphorus is fed, 

 and in many experiments this form has seemed as efficient 

 as the organic. The synthesis in the animal of such com- 

 pounds as the nucleo-proteins can hardly be doubted. 

 The fact of such synthesis does not show that organic 

 phosphorus compounds may not be in general more 

 efficient than inorganic. This question has some economic 

 importance because it is well to know whether so cheap 

 a material as phosphatic rock may be a useful source for 

 fortifying the phosphorus supply of a ration. 



FUNCTIONS OF PROTEIN 



229. Proteins as tissue-formers. While there are at 

 present many unsolved problems relative to the nutri- 

 tive offices of protein, there is no reasonable doubt that 

 the vegetable proteins are the primary and main source 

 of all similar substances in the animal body. From these 

 proteins are formed the muscles, the connective tissues, 

 the skin, hair, horn, and hoofs, and the major part of 

 the tissues of the secretive and excretive organs; in short, 

 that they are the source of a large proportion of the 

 working parts of the animal body. So far, scientific 

 research has not succeeded in demonstrating that a pro- 

 tein is ever synthesized (built up from simple compounds) 

 outside of the plant. It appears that bodies of this class 

 must in the main come to animal life fully elaborated. 

 This is a truth of great significance even in its relation 

 to the nutrition of farm animals. The nitrogenous tissues 

 are those that largely determine the vigor and quality 

 of any animal, and as these are formed rapidly in the early 

 stages of growth, a normal and unrestricted develop- 



