64 PROTEIN DIGESTION IN THE INTESTINE 



Abderhalden's Experiments. Abderhalden and his asso- 

 ciates have by a long series of carefully conducted experi- 

 ments so fully solved many of the problems relating to this 

 field of our study that it is possible to regard it as fairly 

 comprehensible. It is known today that by appropriate 

 and long continued combined action of pepsin, trypsin 

 and erepsin proteid matter may be completely (that is, 

 comparably to total acid hydrolysis) dissociated, and that 

 a mixture of the products of such process is capable of 

 maintaining in nitrogen equilibrium for many weeks ani- 

 mals and human beings, whether in course of growth, in 

 conditions of pregnancy or of lactation. The integrity of 

 the hepatic function is moreover not a matter of necessity 

 in connection therewith ; for Abderhalden and London were 

 able to maintain in nitrogen balance a dog with Eck's fistula 

 upon a diet made up of advanced protein cleavage prod- 

 ucts. Contrary to the belief that only the aggregate of split 

 products from digestive ferment action and not those from 

 acid hydrolysis are capable of replacing protein, Abder- 

 halden has been able to keep in full nutrition for fourteen 

 days a dog fed upon meat completely hydrolysed by boiling 

 with strong sulphuric acid. Eemoval of tryptophane from 

 the mixed digestive products rendered the mixture unfit for 

 maintenance of nitrogen balance. The same inefficiency was 

 found in employing a mixture of aminoacids obtained 

 by cleavage of silk, this proteid being characterized by 

 its high proportion of glycocoll, alanin and tyrosin, and its 

 poverty in a number of the important "building stones" of 

 the typical protein molecule. Similar results were obtained 

 with gelatine, a substance rich in glycocoll, containing very 

 little alanin, and neither tyrosin nor tryptophane. If the 

 glycocoll of the split gelatine is proportionately diluted by 

 addition of the other building-stones which occur in small 

 quantities the combination may be made to be entirely 

 equivalent to protein. It may be questioned whether the 

 dissociated protein is capable of replacing normal protein 



