i2o SCIENCE PROGRESS 



that which Fischer has so subtly carried out has still to be 

 determined. The knowledge of the properties of simple definite 

 chemical compounds has enabled us to separate the amino acids, 

 and thus gain an insight into the ultimate structure of a protein. 

 The study of the polypeptides of definite constitution has led to 

 the isolation of such compounds directly from proteins, and will 

 no doubt help us in finding out the nature of the more complex 

 substances, known as proteoses and peptones. The chemical 

 changes which have given us the most knowledge are the 

 hydrolytic changes, and these are produced by the proteoclastic 

 enzymes, which are more delicate and specific in their action 

 than either acids or alkalies. The study of the action of 

 enzymes upon the proteins and the polypeptides gives us 

 indications as to how the protein may eventually be synthe- 

 sised, by directing the manner in which we combine together 

 the amino acids to form simple polypeptides, these again into 

 greater complexes, and so on until a protein results. We have 

 seen from the above that this method is being carried out, 

 polypeptides having been not only synthesised, but also isolated 

 directly from the protein, and their identity established. 



Bibliography 



■» 



E. Fischer, Untersuchungen ilber Aminosauren, Polypeptide, und Proteine, 

 Berlin, 1906. The researches dealing with the amino acids and polypeptides 

 are contained in the Berichte der Deut. Chem. Ges, vols. 32-9 ; those with 

 the hydrolysis of proteins in Hoppe-Seyler's Zcitschrift fiir physiologischen 

 Chemie, vols. 33-49. 



IE. Abderhalden, Lehrbuch der physiologischen Cheniie. Berlin, 1906. The 

 papers on the action of enzymes upon the polypeptides are all contained in 

 Hoppe-Seyler's Zeitschrift fur physiologische Cheniie, vols. 44-9. 

 Other references are . — 



E. Fischer, Ber. 39, 2320, 2893 ; 40, 1501, 1754. 



und Jacobs, Ber. 39, 2942 ; 40, 1057. 



und E. Abderhalden (Dipeptides from Proteins), Ber. 39, 752, 2315 ; Z. f. 



physiol. Client. 51, 264. 

 und Raske, Ber. 39, 3981. 



F. Ehrlich, Biochem. Zeit. 1, 8 ; Ber. 37, 1809 ; Zeit. Ver. Riibenzuck. Ind. 



1905, 539- 

 Bouveault et LOCQUIN, Compt. Rend. 141, 115. 

 H. Leuchs u. W. Geiger, Ber. 39, 2644. 

 P. A. Levene u. W. A. Beatty, Ber. 39, 2060. 

 O. Cohnheim, Zeit. physiol. Chem. 49, 64. 

 KOSSEL u. Pringle, Zeit. physiol. Chem. 49, 301. 

 Osborne and Clapp, A met: J. Physiol. 18, 123. 



