PROTEIN METABOLISM 81 



obtained by hydrolysis with acid were of no use. In a recent 

 paper, it is true, Henriques and Hansen 1 have shown that the 

 acid products can act to some extent as sparers of protein. 

 How, then, do the acid hydrolysis products differ so much in 

 this vital action from the products obtained by digestion with 

 ferments ? Is it that by the more active boiling acid products 

 which are of absolute necessity for the maintenance of life 

 are too far broken down, or is it perhaps due, in part at 

 least, to the racemisation which takes place ? One series of 

 bodies which are known to be formed in tryptic digestion, 

 and not during acid hydrolysis, the polypeptides — bodies 

 formed by the linking together of two or more amino acids — 

 cannot play any part, as it has been shown (Henriques and 

 Hansen) that when they were removed by precipitation 

 the monamino acids which were left sufficed. Whatever 

 the cause, the main fact still stands that animals fed with 

 acid hydrolysis products perish, whereas animals fed with 

 ferment digest products not only live, but may even thrive 

 on them. 



As regards the statement that the products of protein 

 digestion were absorbed in the form of albumoses and peptones, 

 it rested mainly on the work of Salvioli, 2 carried out many 

 years ago. This worker stated that if he isolated a loop of 

 intestine, and into it put the products in question (albumoses 

 and peptones), on perfusion with blood he found that they 

 disappeared. Further, Salvioli was unable to detect them in 

 the blood used for perfusion, therefore he concluded that the 

 absorbed products were regenerated to more complex bodies 

 before they reached the blood. Recently the writer, working 

 in conjunction with Dr. Leathes, 3 repeated the work of Salvioli, 

 and found that albumoses and peptones introduced into the 

 loop of intestine did indeed disappear, but the interpretation, 

 supported by analytical data, was quite other. We found that 

 the peptone, etc., introduced into the loop was merely split 

 up into simpler bodies which do not give the biuret reaction, 

 in all probability due to the action of the ferment erepsin. 

 If it be due to the erepsin, then this ferment could not have 

 acted intracellularly as Cohnheim holds, as so far as we could 



1 Henriques and Hansen, Zeit. f. physiol. Chem. 49, 1906, 113. 



2 Salvioli, Du Bois Reymond's Archiv, 1880, Suppl. p. 95. 



3 Cathcart and Leathes, Joum. of Physiology, 33, 1906, 462. 



