CHAPTER I 



GENERAL CONSIDERATIONS EXPERIMENTAL TRIALS 

 IN PRACTICE 



T INVESTIGATIONS on the metabolism of material 

 * and energy in animals have shown that animal 

 heat, muscular energy, and body fat can arise from 

 proteins as well as from fats and carbohydrates, and 

 that a liberal supply of nitrogen-free nutrients allows 

 of the food protein being reduced to a certain 

 quantity without detriment to the utility of the 

 animal. This many-sidedness which the animal 

 possesses in dealing with its nutrients and the margin 

 which is thereby allowed in the composition of the 

 ration is of great importance in practice. If the 

 cost of raising and procuring digestible protein 

 was about the same as it is for digestible carbo- 

 hydrates, it would be of little importance whether 

 slightly more proteins were given than necessary, 

 for these substances are without exception able to 

 perform the functions of carbohydrates and fats. 

 But as at the present time protein matter is very 

 considerably dearer than carbohydrates, it is 



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