ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 309 



alone it might well play a role not inferior to that of acid- or 

 alkali-pro teinase (pepsin or trypsin). Not only does protease 

 act on casein directly, but it is able to bring about the split- 

 ting of proteoses and peptones as energetically and as rapidly 

 as either acid- or alkali-pro teinase. In fact, it need not 

 surprise us if in the near future we discover that some of the 

 cleavages of protein which we have thus far attributed to 

 alkali-proteinase are in reality brought about through the 

 protease existing beside the proteinase as an impurity. 



Protease is found not only in the secretions of the small 

 intestine but also in the cells of the intestinal mucosa. Since 

 much more is found in the latter location than in the former, 

 it may well be concluded that the protease within the cells 

 is of greater physiological importance than that contained 

 in the secretions. Self-apparent also is the fact that the 

 power of diffusion possessed by the proteoses in part, by the 

 peptones (in KUHNE'S sense) in much larger part, plays an 

 important role in rendering the protease found in the cells 

 an active agent in the demolition of the protein molecule. 



The following experiment l illustrates the rapidity with 

 which a peptone solution disappears from the intestine. 

 A loop of intestine 50 cm. long is carefully taken out of the 

 abdominal cavity of a dog and after being ligatured at both 

 ends is opened and well washed. 39 c.c. of a peptone solution 

 containing 0.49 gm. nitrogen are introduced into the intestine 

 and the loop replaced in the abdominal cavity. At the end 

 of an hour the loop is again taken out and the amount of 

 unabsorbed peptone solution determined. It is found that 

 0.296 gm. nitrogen has been absorbed, in other words, over 

 60 percent. 



When the 95 cm. of intestine which were not used in this 

 experiment are taken into consideration, simple calculation 

 shows that this dog would have been able to absorb from its 

 entire small intestine more than 0.8 gm. nitrogen per hour. 



: Zeitschr. f. physiol. Chemie, 1902, XXXVI, p. 13, 



