DIGESTION OF THE FOOD 37 



carbohydrates — potatoes, mangels, etc. — are added 

 to a ration poor in crude protein, the digestibility 

 of the various components of the food is diminished. 

 As regards the explanation of this phenomenon, 

 it is known that after the addition of such materials 

 as have been mentioned, the faeces of the animal 

 are considerably richer in nitrogenous substances. 

 These do not come from the food, but from the 

 digestive juices and from the mucous membrane of 

 the intestines. On analysing such faeces more 

 crude protein is found than when the basal ration is 

 given without any additions. As the calculation 

 of the quantity of digested crude protein is made 

 by subtracting that found in the dung from that 

 present in the food, the difference in crude protein 

 is less where additions of the kind mentioned have 

 been made. The depression of the digestibility of 

 crude protein by the addition of starch, etc., would 

 accordingly only be an apparent one, and would 

 be explained by the presence of waste nitrogenous 

 products of metabolism in the faeces. Further, it 

 may be supposed that the bacteria, which are 

 present in large quantities in partly digested food, 

 nourish themselves on the easily digestible sub- 

 stances, such as starch or sugar, when these are 

 added, whilst the constituents of the food are acted 

 upon in a less degree. The addition of starch or 

 sugar to hay would protect the latter from disso- 

 lution and decomposition by bacteria. In conse- 



