166 LECTURE VIII. 



Tryptophane, as well as cystine, can be obtained just as quickly as 

 tyrosine; the former being easily recognized by the violet color which is 

 formed when bromine water and acetic acid are added to the digesting 

 liquid. The remaining amino acids are obtained later on. This has been 

 successfully proved in the case of glutamic acid. The following per- 

 centages of the total amount of this amino acid occurring in edestin, were 

 obtained: 



Alanine, leucine, amino-valeric acid, and aspartic acid, acted in the 

 same manner; while a-proline and phenylalanine could, in no case, be 

 separated from a digesting fluid. 



The following observations have given us an explanation of this peculiar 

 behavior: l If we digest casein, edestin, serum-globulin, egg-albumin, 

 hemoglobin, or fibrin with pancreatin, 2 or even with pancreatic juice, we 

 obtain all the mono-amino and di-amino acids in the digesting mixture, 

 with the exception of proline and phenylalanine. These amino acids do 

 not occur, or, if so, only in minute quantities, even when tryptic digestion 

 precedes that of the pepsin-hydrochloric acid. 3 Now we can precipitate 

 even from a greatly diluted digesting mixture, by means of phospho- 

 tungstic acid, a product which apparently is a mixture of highly compli- 

 cated compounds. It sometimes gives the biuret reaction; then again, 

 no result is obtained according to the time of digestion. No free amino 

 acids can be isolated from this product, although we can obtain such by 

 hydrolysis with fuming hydrochloric or 25 per cent sulphuric acid. In the 

 presence of small amounts of alanine, leucine, aspartic acid, and glutamic 

 acid, we obtain large amounts of a-proline and phenylalanine; and, in 

 those proteins containing glycocoll, even this amino acid, in amounts 

 approximating those contained in the protein in question. The proteins 

 evidently contain groups which resist the action of ferments. Of 

 especial interest is the fact that here also the rate at which the individual 

 amino acids are separated varies. 



From these investigations it is clear that fermentative decomposition is a 

 progressive one. An immediate disruption of the protein does not occur. 



1 E. Fischer and E. Abderhalden: Z. physiol. Chem. 39, 81 (1903). 



3 A commercial preparation of pepsin was used in this experiment, consequently 

 impure. It is very probable that the latter disintegrated albumin more than the gastric 

 Juice alone would do. 



8 E. Fischer and^. Abderhalden: Z. physiol. Chem. 40, 215 (1903). 



