DIGESTION OF THE PROTEINS 243 



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ease and certainty the accumulation of amino-acids in the blood which 

 accompanies absorption after a meal rich in protein. 



The absorption of amino-acids from the intestine and their conse- 

 quent presence in the blood has also been very beautifully demon- 

 strated by Abel, employing his method of Vividiffusion. This method 

 consists in deflecting a fraction of the blood-stream and causing it to 

 pass through a series of collodion-tubes before returning to the general 

 circulation. The collodion-tubes are immersed in a salt solution of the 

 same concentration as the inorganic salts in the blood, so that dif- 

 fusible substances other than inorganic salts dialyze out of the blood 

 into the saline solution. By renewal of the saline solution considerable 

 quantities of the diffusible substances in blood may be collected and, 

 among others, various amino-acids (Fig. 8). 



FIG. 8. Abel's vividiffusion apparatus. (After Macleod.) 



It is thus evident that the protein constituents of the dietary are 

 absorbed into the circulation in the form of their amino-acid compon- 

 ents, some selection of the amino-acids transmitted to the blood being 

 exercised by the intestinal epithelium. The question now arises, 

 where, and in what way, these amino-acid fragments are resynthesized 

 into protein. 



Amino-nitrogen determinations show that the excess of amino-acids 

 which accumulates in the blood after a meal very rapidly disappears, 

 while coincidently a considerable increase in the free amino-acids is 

 found to have taken place in the tissues. The amino-acids are there- 



