CII. XXXVI.] ABSORPTION 545 



It is somewhat difficult to find the ammo-acids iu the blood 

 during absorption, for several reasons: (1) the absorption during 

 any given time is slow, and the products are diluted with the whole 

 volume of the blood ; (2) the presence of coagulable proteins in the 

 blood in large quantity renders a search for the amino-acids difficult ; 

 and (3) when the amino-acids get into the blood they do not 

 accumulate there, but are rapidly removed by the cells of the 

 tissues. In spite of these difficulties, Leathes, Howell, and, later, 

 Folin have succeeded in demonstrating that during absorption the 

 non-protein (that is, the ammo-acid) nitrogen of the blood increases. 

 The hypothesis that proteins are synthesised during absorption in 

 the intestinal wall from amino-acids was for long held by Abder- 

 halden, but in view of these researches, he has finally aban- 

 doned it. 



"We have now a rational explanation of why it is that the 

 organism can construct the proteins peculiar to itself and maintain 

 its chemical individuality, although the food taken varies so widely 

 in composition. 



If a man wants to build a house from the bricks of another 

 previously built house, he naturally takes the latter to pieces first, 

 and uses the bricks most suitable for his purpose, and arranges them 

 in a different way to their previous arrangement. The Germans 

 have recently coined the expression Bausteine (or building stones) 

 for the final products of proteolysis with the same underlying idea ; 

 these fragments are rearranged by the tissue cells into tissue- 

 protein, which is different architecturally from the food-protein. 



Abderhalden has published a very striking experiment in confirmation of this 

 view. He collected the blood of a horse, separated out the various proteins of the 

 plasma, and estimated in each the yield of certain cleavage products (glutamic acid 

 and tyrosine) which resulted from hydrolysis. He then fed the horse so that it 

 formed new blood, but the only protein given was gliadin, a vegetable protein, 

 which is remarkable for its high percentage yield (37-3) of glutamic acid. But in 

 the regenerated blood proteins the percentage yield of glutamic acid was not 

 increased at all ; they exactly resembled the proteins previously present. 



It is a far cry from the highly specialised organism of the horse to the proto- 

 plasm of the simple mould known as Aspergillus niger ; nevertheless, the same 

 general rule holds ; the protein matter present yields on hydrolysis, glycine, 

 alanine, leucine, glutamic and aspartic acids, but aromatic products, such as 

 tyrosine and phenylalanine, were not discovered. The mould was then cultivated 

 on media of widely varying composition, but the protein formed in the living 

 protoplasm remained constant in composition, and is thus independent of the 

 composition of the nutritive medium. 



What, then, if this is the case, would be the fate of food proteins introduced 

 directly into the blood-stream without the intervention of the alimentary digestive 

 processes? If the preliminary cleavage in the gastro-intestinal tract is absol- 

 utely necessary, one would anticipate that a foreign food protein (such as 

 edestin from hemp seed, or excelsin from Brazil nuts) administered by intravenous 

 or intraperitoneal injection would not be assimilated, but would be cast out of the 

 body in one or more of the excretions. But Mendel and Rockwood found that 

 they were not eliminated in either urine or bile. In some cases, a proteose 



2 M 



