DIGESTION OF THE FOOD 39 



say, cotton-seed cake meal is added to the ration, 

 no traces of starch are found in the dung, for diges- 

 tion has been complete. The addition of non- 

 protein nitrogenous substances (amides and amino 

 acids, etc.) acts similarly to the protein, and raises 

 the digestibility when it is depressed by large doses 

 of carbohydrates. After thorough investigation of 

 this phenomenon it has been proved that a complete 

 digestion of all constituents of the food is assured 

 if the total ration contains 8-10 parts of digestible 

 nitrogen-free substance to each part of crude pro- 

 tein. This ratio applies particularly to ruminants ; 

 for pigs less protein is necessary, and may be 

 placed at i part to 12 parts nitrogen-free extract. 

 If the proportion of carbohydrates is in excess of 

 these figures, then some of the otherwise digestible 

 material passes into the faeces. 



6. The only other substances whose action upon 

 the digestibility has been tested are lactic acid, 

 calcium carbonate, and common salt. With all 

 these, however, no influence, favourable or un- 

 favourable, has been noticed. With regard to lactic 

 acid, which is present in considerable quantities 

 (up to 3%) in acid food-stuffs, such as silage, it is 

 known that continued feeding of large quantities 

 of this material injures the teeth, and so mastica- 

 tion becomes imperfect. Disturbances of the diges- 

 tive organs are also liable to arise, and so the food 

 is not properly utilised, which means loss. Without 



