METABOLISM AND FOOD 69 



no protein-saving action. All food nutrients, then, 

 which are capable of conversion into fat in the body 

 possess at the same time the power of economising 

 protein. Whether the nitrogen compounds of non- 

 protein nature which contain more carbon than 

 asparagine can take part in the formation of fat 

 has not yet been decided. In fact, the whole ques- 

 tion as to the position of these materials in the food 

 supply requires more investigation. As far as has 

 been proved, it may be said that ruminants receiving 

 a food poor in protein, but rich in non-protein, 

 can utilise the latter to make flesh, but not fat, 

 the change being brought about by help of the 

 bacteria in the partly digested food. Some further 

 experiments on this subject will be given in the 

 chapter on the feeding of milch cattle. 



(c) The effect of nitrogen-free nutrients. 



The different nitrogen-free constituents of the 

 food the fats, the nitrogen-free extract, and the 

 crude fibre, exercise in general the same effect. 

 The fats are the most concentrated form of nutrient ; 

 on digestion they suffer no severe loss, for they 

 are not apparently acted upon by bactena or 

 the digestive juices, except that the latter split 

 them up into free fatty acids and glycerine. 

 Immediately after entrance into the fluids of the 

 body, these components are again formed into fat. 



