CHEMICAL DYNAMICS OF ANIMAL NUTRITION 159 



This disintegration proceeds for three or four hours, 

 after which in most cases it entirely ceases, at any rate 

 for some time (Lane-Clay pon and Schryver, Journ. 

 Physio I. 31, pp. 173-4). In the researches just quoted, 

 the residual nitrogen was determined in the filtrate 

 from the coagulum, after precipitating with trichloracetic 

 acid in boiling solution. The preliminary researches of 

 Part II shew that when this method is used, nearly all 

 the residual nitrogen passes into the filtrate, at any rate 

 in fairly dilute solutions. Now the amount found by 

 this method of analysis in the mucous membrane of 

 intestine of five animals was equivalent to 17*8 c.c. 

 H a so 4 for 5 grams of tissue if the residual nitrogen 

 be determined before incubation. After incubation for 

 4 hours, however (that is to say after the first rapid 

 disintegration had come to a standstill), this number 

 rose to about 32 c.c, H a so 4 . This is very nearly the 

 same amount as that found by coagulating the tissue, 

 when dried by sodium sulphate according to the method 

 described in Part II. This seems to indicate that part, 

 at least, of the bodies represented by the residual 

 nitrogen is in some form of chemical combination with 



O 



the bioplasm. 



What conclusions are to be drawn now from the above results ? 

 In the first place, there is no evidence that the products of 

 tryptic digestion as such can circulate in indefinite quantities in the 

 blood-stream. How, then, are we to explain their fate after leaving 

 the alimentary tract ? What light do the above results throw on this 

 subject ? 



Four sets of facts are of special significance in connection with 

 these questions ; they are : 



(i) The percentage of residual nitrogen is very high in the 



mucous membrane of the intestine, a tissue most 



intimately connected with the nitrogenous metabolism. 



(ii) In the limited number of cases examined, it is higher in 



carnivora than in the herbivora. 



