THE ABSORPTION OF THE FOOD-STUFFS 845 



food-stuffs, in the carbon itself, and is derived from the combustion 

 of the carbon of the molecule under the influence of the oxidising 

 processes of the body into carbon dioxide. The experimental decision 

 of this question was first attempted by 0. Loewi, who found that it 

 was possible to keep a dog in a state of nitrogenous equilibrium on 

 a diet containing fat, starch, and a pancreatic digest of protein which 

 contained no substances which would give the biuret test. These 

 results have been confirmed for carnivora by Henderson, by Luthje, 

 by Abderhalden and Rona, and by Henriques and Hansen. According 

 to Abderhalden, it is possible to keep an animal alive when the 

 nitrogen in his food is represented entirely by the end-products of 

 pancreatic digestion. The same result cannot be attained by the 

 administration of the products of acid hydrolysis of protein, but 

 this may be due either to the racemisation of the amino-acids under 

 the action of the strong acid, or to the fact that the acid splits up 

 certain polypeptide groupings which are still contained in the trypsin 

 digest, and which possibly cannot be synthetised by the cells of the 

 body. 



We are justified therefore in concluding that while a certain 

 small proportion of the proteins of the food may be absorbed un- 

 changed, a much larger proportion is taken up as albumoses and 

 peptones or as amino-acids. The albumoses and peptones are, how- 

 ever, rapidly changed in the mucous membrane itself into amino-acids, 

 which we may regard as the form in which practically all the protein 

 of the body is presented to the absorbing mechanisms of the alimentary 

 canal for absorption and for passing on into the circulating fluids. 



THE FATE OF THE AMINO-ACIDS AFTER ABSORPTION BY 

 THE INTESTINAL EPITHELIUM. During a condition of starvation 

 the normal protein requirements of the body, or rather of the active 

 tissues, are met at the expense of the less active tissues. The protein 

 characteristic of any tissue can be taken down, removed to another 

 part of the body, and built up into the protein characteristic of some 

 other active tissue. It is difficult to conceive that such a transference 

 and transformation could occur in any other way than by a more 

 or less thorough disintegration of the protein molecule at one place 

 and its synthesis at the other, and we know from the researches of 

 Hedin and others that every tissue contains intracellular ferments 

 which are capable of effecting the disintegration of the protein mole- 

 cule, and are responsible for the autolytic degeneration of tissues 

 after death. If therefore the normal interchange of protein between 

 the tissues is accomplished, as we know it to be in plants, by the 

 disintegration of the proteins into their constituent amino-acids 

 and their subsequent reintegration, there is no a priori reason to 

 believe that the blood carries the proteins from the alimentary canal 



