v INTERNAL BESTITUTIVE SECRETIONS 293 



Sulvioli in the excised loop of intestine into which peptone only 

 had been introduced, has the same secretory origin, i.e. it is derived 

 from succus entericus secreted during the absorption and subse- 

 quent regeneration of the peptone. 



The disappearance of the peptone artificially introduced into 

 the loop of intestine may therefore be the result of a conversion, 

 not into larger complexes, but (at least partially) into simpler 

 crystallisable complexes (amino-acids). 



We already know from the work of Kiihne (p. 211) that 

 the protracted action of trypsine upon peptone may result in very 

 simple products. Neumeister (1890), who observed the disappear- 

 ance of peptones from the blood diluted with peptone solution in 

 which he had placed freshly excised fragments of intestine, came 

 to no definite conclusion in regard to the disappearance of 

 peptones by conversion into more complex products ; but he 

 brought forward the other possibility, viz. the formation of aniino- 

 acids, already suggested by Briicke, by Voit, and particularly by 

 Pick, since he was able to show the presence of leucine and 

 tyrosine, although only in small quantities. 



Capparelli (Catania, 1899) suggested the same account of the 

 conversion of peptone in the intestine. He introduced a solution 

 of commercial peptone into an empty loop of intestine in a dog 

 that had fasted 1-3 days, after tying it at the ends and isolating it 

 from the mesentery so as to prevent absorption by the blood, after 

 which it was replaced in the stomach. On testing the fluid after 

 1-1| hours the peptone had disappeared. The same occurred in 

 vitro on mixing shreds of intestinal mucous membrane with peptone 

 solution, as also with a mixture of various digestive enzymes, or 

 with trypsin alone. In all these cases he found that the products 

 of peptone conversion were highly soluble in water, insoluble in 

 alcohol, dialysible, with a rotary power different from that of the 

 original peptone solution. He concluded that he was dealing with 

 a complex simpler than peptone, which he was, however, unable to 

 identify. 



0. Cohnheim has recently formulated more concrete opinions 

 on the same subject. As we saw on pp. 127, 212, he found that the 

 intestinal mucous membrane actually contained a special enzyme 

 which he called erepsin, which has this very property of breaking 

 up the proteoses and peptones into smaller complexes (amino- 

 acids). Neumeister and Capparelli may both be regarded as the 

 immediate precursors of the discovery of erepsin. 



According to Kiihne, Cohnheim, and others, absorption of 

 proteins takes place after their more or less complete conversion 

 into aniino-acids. Part of these are synthetised by the mucous 

 membrane of the intestine, part, on the contrary, which are 

 absorbed unchanged, are directly consumed by the tissues, or 

 undergo within their depths the synthetic processes by which 



