300 PHYSIOLOGY OF ALIMENTATION. 



amount of peptones in the blood leaving the intestines is not 

 increased is an inconclusive argument, for they are not in- 

 creased to any marked degree even under conditions when 

 we know that the protein is being absorbed in the form of 

 the soluble digestion products. From our knowledge of the 

 almost universal distribution of proteolytic enzymes through- 

 out the tissues and fluids of the animal body and their great 

 activity in the living organism, it does not seem too hazardous 

 to believe that even that portion of a protein solution which 

 is believed to be absorbed in the "native " state is in reality 

 absorbed in the form of peptones, or still more probably in 

 the form of the simple crystalline products of proteolytic 

 activity. 



But even if we allow that proteins may be absorbed as 

 such the amount that passes through the wall of the alimen- 

 tary tract in this form must be small. Just how small cannot, 

 of course, be said, but the knowledge that adequate means 

 exist in the body to split all the protein of an ordinary meal 

 in the course of a few hours, and that the diffusion velocity 

 of even such complex substances as the peptones is several 

 times that of the proteins from which they are derived, in- 

 dicates that under ordinary circumstances only a small 

 fraction, if any at all, of the protein of an ordinary meal is 

 absorbed in an unchanged state. 



If protein is not absorbed as such, then in which of the 

 various forms into which it is -changed under the influence 

 of the proteolytic ferments is it absorbed? This is a ques- 

 tion which it is exceedingly difficult to answer, for the multi- 

 tude of experiments that have been performed by many 

 different investigators have not in any sense yielded results 

 which are either entirely satisfactory or capable of only one 

 interpretation. The burden of experimental evidence seems 

 to indicate, however, that most, if not all, protein is absorbed 

 in the form of the very simple crystalline products of pro- 

 teolysis with which we became acquainted in the discussion 

 of acid- and alkali-pro teinase (pepsin and trypsin), and pro- 



