THE ABSORPTION OF THE FOOD-STUFFS 745 



variations in the amount of lymph to be obtained in this way bear no 

 relation to the condition of the animal as regards the state of digestion. Nor 

 do we find any appreciable increase in the amount of lymph flow or in the 

 amount of proteins contained in this lymph during digestion. The small 

 increase observed by Asher and Barbara would be sufficiently accounted for 

 by the increased blood-supply to the intestines during digestion, and is 

 insufficient to account for the absorption of any appreciable quantity of the 

 protein which is being taken up from the alimentary canal. Moreover it was 

 shown by Schmidt Miilheim that the absorption of proteins was not inter- 

 fered with as the result of ligature of the thoracic duct, and that after this 

 duct had been ligatured the ingestion of proteins was followed at the usual 

 interval by the increased output of urea which is the invariable concomitant 

 of protein absorption and assimilation. We must therefore conclude that 

 the products of protein digestion are taken up by the epithelial cells and 

 passed on by these into the blood-vessels. 



During the absorption of a protein meal changes have been described by various 

 observers in the structures of the villus. In nearly every case there is marked increase 

 in the number of mitotic figures in the epithelium lining the follicles of Lieberkiihn. 

 According to Hofmeister there is during absorption an increase in the number of 

 leucocytes in the villi, and this observer ascribed an important function to these 

 eclls in the absorption of protein. Heidenhain showed that this increase of 

 leucocytes was not constant in all animals, and bore no relation to the amount of 

 absorption that was taking place, and was quite inadequate to account for the total 

 absorption that was carried on. On the other hand, several observers have described 

 changes in the epithelium as the result of protein digestion. According to Reuter the 

 epithelial cells become swollen, their protoplasm stains less deeply, and at their basal 

 ends the cells' limits disappear, the protoplasm being apparently distended with hyaline 

 coagulable material (Fig. 352). Reuter regards this appearance as a direct expression 

 of the taking up of proteins in a dissolved form and their conversion near the bases 

 of the cells into coagulable proteins ; but further evidence on this subject is necessary 

 before we can attach much importance to such an interpretation of the appearances 

 observed. 



Under the influence of the gastric juice the proteins of the food are 

 resolved during their stay in the stomach into albumoses and peptones. In 

 the small intestine the process of hydration is carried further, the trypsin of 

 the pancreatic juice carrying the proteins through the stage of secondary 

 albumoses and peptones, and converting them into a mixture of amino-acids 

 and polypeptides. The same end-products result from the action of the 

 erepsin of the intestinal wall on the albumoses and peptones produced by 

 gastric digestion. The digestive juices finally reduce the proteins therefore 

 to a mixture of amino-acids, with a certain remainder of polypeptides con- 

 sisting of two or three of the amino-acids associated together, which do not 

 undergo further disintegration under the action of the intestinal ferments. 

 The final products give no biuret test. The first question we have to decide 

 is to what extent the proteins are reduced to their ultimate hydration pro- 

 ducts before absorption. We have evidence that protein may be absorbed 

 by the small intestine without having undergone any hydration whatsoever. 

 The absorption of serum protein has been discussed already in dealing with 

 the mechanism of absorption of salt solutions from the gut. In a series of 



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