DIGESTION 



405 



Assuming the starch to be completely digested, the results are as 

 follows i 1 



PERCENTAGE DIGESTIBILITY. 



The depression in digestibility of protein may be in part due to 

 increased excretion of metabolic products. As we have seen, 

 2.5-3.1 grams of protein are excreted from every 100 grams of 

 digested dry substance, and the additional quantity of protein 

 excreted corresponds very nearly to the increase which would be 

 caused by the addition of starch. However, we do not yet know 

 the cause of the decreased digestion. Other carbohydrates, as, 

 cane sugar, pectin, and purified cellulose, have the same effect as 

 starch in decreasing digestibility. 



An increase of protein can partly or completely eliminate the 

 depression caused by addition of carbohydrates. For example, 

 Haubner found that the starch appeared in the excrement of 

 sheep fed on potatoes, but when rape cake was added to the ration, 

 starch was no longer excreted. Many exact digestion experi- 

 ments have proved that the addition of protein can increase the 

 digestibility of a ration poor in protein. 



Non-albuminoid nitrogenous compounds, such as asparagin, 

 exert a similar effect. For example, Weiske found a ration 

 nearly free of nitrogen digested 86 per cent., with addition of 

 asparagin or fibrin it was digested 92 per cent. Kellner observed 

 a similar action when asparagin or ammonium acetate was used. 



Concentrated feeding-stuffs exert an influence on digestion 

 according to their content of digestible protein or carbohydrates. 

 Foods poor in protein, as beets and potatoes, exert a depressing 

 1 Landw. Versuchs-stat., 1894, p. 470. 



