fertilizer control station. 381 



Artificial Digestion Compared with Results Obtained from 



Experiments with Animals. The Errors Intolved in 



Digestion Experiments with Animals. 



Several investigators have proposed within a comparatively recent 

 time to measure the digestibility of cattle foods by the solubility of 

 their protein in certain artificial solutions of pepsin and pancreas ex- 

 tract that are similar in action to the digestive fluids of the stomach and 

 intestines of animals. In testing this method comparisons have been 

 made between the results obtained b}' the use of artificial solutions 

 and by experiments with animals. These comparisons have brought 

 into especial prominence the errors involved in the coeflScients of 

 digestibility for protein as determined in the ordinary way. The 

 main facts developed by several investigations, which bear upon the 

 above points, are summarized in what follows : 



(1) The feces of animals contains varying quantities of bile com- 

 pounds, epithelial cells, mucus, &c., some of which contain nitrogen. 

 These cause an error by increasing the apparent amount of undi- 

 gested protein. 



(2) The quantity of these substances appearing in the feces is 

 stated to vary within wide limits with the amount of digestible ma- 

 terial in the food eaten. 



(3) When comparisons of artificial digestion and the results of 

 experiments with animals have been made with the same material, 

 the former method has invariably given higher coefficients of diges- 

 tibility for protein, the difference being somewhat inversely to the 

 amount of protein in the food. 



(4) It is claimed that the artificial method gives correct results 

 and that these diflferences are due to the presence in the feces of 

 certain gall and intestinal products alread\^ mentioned, which do not 

 belong to the undigested food residue, and which cause the digesti- 

 bility of protein to appear less than it really is, when this is measured 

 by the difference between the nitrogen of the food and that of the 

 feces. 



(5) Stutzer* has proposed that the undigested protein of the food 

 be measured b}' the nitrogen left in the feces after submitting it to 

 digestion with a pepsin solution. FfeiflTert has compared the re- 

 sults obtained in this way with those of the artificial pepsin-pan- 



*Zeit. Phys. Chemie X, p. 157. 

 flbid X, p. 561 and XI, p. 1. 



