120 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, Uniersuchungen tiber Aminosduren, 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 Zettschrift fiir physiologischen 
Chemie, vols. 33-49- 
E. ABDERHALDEN, Lehrbuch der physiologischen Chemie. Berlin, 1906. The 
papers on the action of enzymes upon the polypeptides are all contained in 
Hoppe-Seyler’s Zeitschrift fiir phystologische Chemie, vols. 44-9. 
Other references are :— 
E. FISCHER, Ber. 39, 2320, 2893 ; 40, 1501, 1754. 
und Jacogs, Ber. 39, 2942 ; 40, 1057. 
und E. ABDERHALDEN (Dipeptides from Proteins), Ber. 39, 752, 2315; Z 
physiol. Chem. 51, 264. 
und RASKE, Ber. 39, 3981. 
F. EHRLICH, Biochem. Zeit. 1,8; Ber. 37, 1809; Zect. 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, Ze?t. physiol. Chem. 49, 301. 
OSBORNE and CxappP, Amer. J. Physiol. 18, 123. 
