310 PHYSIOLOGY OF ALIMENTATION. 



This figure, which is by no means the highest that might be 

 given for experiments of this sort, indicates how rapidly 

 peptones disappear from the small intestine, especially when 

 it is added that at this rate a dog could absorb in one hour 

 nearly enough nitrogenous material to suffice for its daily 

 existence. 



It remains for us to show that this rapid absorption of 

 peptones is determined by the action of protease upon them, 

 whereby they are dissociated into the very diffusible crystal- 

 line digestion-products which have been enumerated above; 

 and that this dissociation is not brought about by such a 

 ferment as alkali-pro teinase (trypsin). While under ordi- 

 nary circumstances both alkali- and acid-proteinase are 

 active in bringing about the dissociation of the protein which 

 we take in with our food, under the experimental condi- 

 tions outlined above this is not the case, for a well-washed 

 loop of intestine contains no alkali-pro teinase (trypsin), or 

 at best only very little. This has been repeatedly shown 

 by experiments in which proteins, such as fibrin, are intro- 

 duced directly into the small intestine, when it has been 

 found that they disappear very slowly (in days or even 

 weeks). 



