50 THE AMINO ACIDS 



tine, undergo intestinal digestion and eventually be 

 absorbed in the form of protein decomposition pro- 

 ^ducts. Experiments to test this point have been carried 



( out. It has been shown that when a solution of casein 

 \ is introduced directly into the blood stream a small part 



Lmay reappear in the bile. 



On the other hand, when egg white or serum are 

 injected subcutaneously into dogs and goats a goodly 

 portion of the protein may be eliminated in the form 

 of non-coagulable protein. This observation would 

 tend to demonstrate the non-utilization of the injected 

 protein as such and points out that it undergoes a 

 change in its transit through the organism. In the 

 blood also a non-coagulable protein, perhaps a proteose, 

 is detectable, and a marked increase in nitrogen of 

 the urine in the form of urea is apparent. Indeed, 

 nitrogen equilibrium may be maintained under these 

 circumstances when animals are given a sufficiency of 

 carbohydrates. 



In most of the work on parenteral absorption of 

 protein the material introduced did not possess enough 

 differentiation from other body proteins to distinguish 

 it from them. Borchardt conceived the idea of inject- 

 ing a protein with peculiar properties and chose hemi- 

 elastin; after intravenous injection this substance was 

 present in the wall of the small intestine, and Borchardt 

 concluded that the protein was either on its way for 

 excretion by the gut or further changes by the intes- 

 tinal juices to prepare it for utilization by the tissues, 

 or finally had found its way into the intestine by way 



