192 LECTURE IX. 



content ourselves with a knowledge of their methods of action. There is no 

 doubt that with the assistance of these synthetic polypep tides, new questions 

 will arise in this connection and will probably be solved. We shall be 

 able to determine whether the various kinds of animals possess the same 

 kinds of proteolytic ferments, or those which act differently. We are 

 inclined to the latter belief, at least in special cases. We know that the 

 feathers of birds and the hair of the Mammalia are subjected to the 

 inroads of parasites, being eaten up by them. These minute animals must 

 possess much more vigorous proteolytic ferments than have been vouch- 

 safed to us, because the keratins are, so far as we know, entirely indi- 

 gestible by vertebrates. We also hope to obtain a complete explanation 

 of the differences between the action of trypsin and of pepsin by studying 

 the relations of these proteolytic ferments toward the polypeptides. 1 Up 

 to the present time none of the synthetic peptides have been acted upon 

 by pepsin. 2 It is possible that the amino acid chains utilized were not 

 long enough. In fact, pepsin-hydrochloric acid seems to decompose albu- 

 min in a manner entirely different from that characteristic of trypsin. 3 

 Evidently peptones, and other cleavage-products which do not give the 

 biuret reaction, are produced. There are, however, no amino acids 

 formed. 1 The significance of gastric digestion is still quite obscure. 

 It may possibly be that it causes a preparatory cleavage of the albumins, 

 so that the trypsin has more opportunity to act. It can also be shown 

 experimentally that tryptic digestion is hastened and proceeds much 

 farther, if a pepsin-hydrochloric acid one precedes it. 



With the assistance of the polypeptides we also hope to get an insight 

 into cell metabolism. It has already been demonstrated that the tissues, 

 especially the liver, contain proteolytic ferments, which are capable of 

 dissolving bonds between amino acids that are unattacked by trypsin. 

 Thus, an extract from the liver will split glycyl-glycine completely into 

 its components. 4 By extending these investigations to include the various 

 organs, we will ultimately succeed in finding those which are the most import- 

 ant factors in the decomposition of the albumins. 5 The polypeptides will 

 also be of great service to us for comparative purposes. It will be of the 

 greatest interest to learn whether the representatives of the various ani- 

 mal classes will disintegrate the individual polypeptides in the same manner, 

 or whether there will be differences in the decomposition products. 



From all these problems it is at once obvious how important is the 

 synthetic linking together of the amino acids into the polypeptides for all 

 branches of biological science. 



1 E. Abderhalden and P. Rona: Z. physiol. Chem. 47 (1906). 



2 E. Fischer and E. Abderhalden: ibid. 46, 52 (1905). 



3 E.. Fischer and E. Abderhalden: ibid. 40, 215 (1903). F. Obermeyer and E. P. 

 Pick: Hofmeister's Beitr. 7, 331 (1905). 



4 E. Abderhalden and O. Rostoski: ibid. 44, 265 (1905). 



5 E. Abderhalden and Y. Teruuchi: Z. physiol. Chem. 47, 1906. 



