THE ABSORPTION OF PROTEINS 51 



of the bile. The last hypothesis did not appear likely 

 however, since none of the introduced protein could 

 be found in the liver. 



From the foregoing arguments it is clear that the 

 apparent utilization of parenterally introduced protein 

 may be disposed of in at least three ways: 1. The 

 direct utilization by the tissues, for which there is little 

 or no evidence. 2. The excretion of the injected mate- 

 rial into the intestine where it is subjected to the 

 action of digestive enzymes, finding its way either 

 directly into the intestine or indirectly through the 

 bile. There is little doubt that a certain portion of 

 the injected material is treated in this manner. 3. The. 

 transformation of the native protein in the tissues 

 into smaller fractions such as proteoses, peptones or 

 amino acids. Heilner has suggested that the utilization 

 of parenterally introduced protein is induced by the 

 generation of a specific enzyme capable of bringing 

 about a hydrolysis. 



In the last suggestion it is probable that we have 

 the true explanation for the phenomenon under dis- 

 cussion for Abderhalden and his co-workers have 

 demonstrated that the parenteral introduction of native 

 protein or of peptone gives to the blood serum of the 

 animal the power of decomposing these substances, and 

 this power is destroyed by heating to 60 to 65 C. 

 Over-feeding by mouth confers upon the blood serum 

 the same property. The acquisition of this power on 

 the part of the blood serum may be regarded, as 

 Heilner suggested, as a generation of an enzyme or 



