ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 307 



most varied parent bodies. The alimentary tract then 

 synthesizes from these elements the complex substances 

 found in the blood. In disturbances in general metabolism 

 involving the alimentary tract it is not so much the impaired 

 absorption that is so important as the impaired assimila- 

 tion. That this synthesis of protein plays an important role 

 in the metabolism of the animal has been shown very strik- 

 ingly by ABDERHALDEN and RoNA. 1 These authors were able 

 to keep animals in nitrogenous equilibrium by feeding them, 

 in addition to an ordinary mixture of fats and carbohydrates, 

 casein which had been previously digested through alkali- 

 proteinase, so that 80 to 85 percent of it consisted of amino- 

 acids mixed with simple polypeptides, the remaining 15 to 20 

 percent of more complex polypeptides, but not sufficiently 

 so to give a biuret reaction. 



As agencies capable of such a reconstruction of the albu- 

 min molecule have been mentioned the chemical forces of 

 the epithelial cells themselves and the activities of JULIA 

 BRINCK'S micrococcus restituens. That a microorganism living 

 upon the surface of the alimentary mucous membrane should 

 be of any importance to its host by being able to reconstruct 

 from the products of proteolysis the protein itself (which 

 would again have to be broken up before it could pass through 

 the epithelial cells in any amount) is, no doubt, too improb- 

 able to need serious consideration. There is much more likeli- 

 hood that the chemical forces residing in the epithelial cells 

 are capable of reconstructing albumins from the products 

 of proteolysis. Elsewhere 2 experiments have been dis- 

 cussed which seem to indicate that the activity of the pro- 

 teolytic ferments is reversible. Were this true, then the 

 synthesis of albumins within the epithelial cells lining the 

 alimentary tract, in a way entirely analogous to the syn- 

 thesis of fat in this locality under the influence of lipase, 



1 ABDERHALDEN and RONA: Zeitschr. f. physiol. Chem., 1904, XLII, 

 p. 528; ibid., 1905, XLIV, p. 108. 



2 See p. 140. 



