434 CHEMICAL DISCOVERY AND INVENTION 



enzymes as already explained is unknown and likely to remain a 

 mere subject for conjecture for a long time to come. 



Emil Fischer has expressed his views very clearly in the 

 Faraday Memorial Lecture given in 1907, in accordance with 

 custom, in the lecture theatre of the Royal Institution in London. 

 " Of the numerous attempts to unravel the constitution of the 

 proteins by analytical means," he said, " the only method 

 which has given useful results hitherto is that of hydrolysis. 

 Hydrolysis can be effected by acids or by alkalis and also by 

 digestive enzymes ; the products as is well known, besides 

 ammonia, are albumoses, peptones, and ultimately amino-acids. 

 The wide range of variation in composition of these amino-acids 

 is illustrated in the following table : 



Glycine (Braconnot, 1820) 



Alanine (Schutzenberger, Weyl, 1888) 



Valine (v. Gorup-Besanez, 1856) 



Leucine (Proust, 1818 ; Braconnot, 1820) 



^soLeucine (F. Ehrlich, 1903) 



Phenyl-alanine (E. Schulze and Barbieri, 1881) 



Serine (Cramer, 1865) 



Tyrosine (Liebig, 1846) 



Asparticacid (Plisson, 1827) 



Glutamic acid (Ritthausen, 1866) 



Proline (E. Fischer, 1901) 



Oxyproline (E. Fischer, 1902) 



Ornithine (M. Jaffe, 1877) 



Lysine (E. Drechsel, 1889) 



Arginine (E. Schulze and E. Steiger, 1886) 



Histidine (A. Kossel, 1896) 



Tryptophane (Hopkins and Cole, 1901) 



Diaminotrihydroxy- (E. Fischer and E. Abderhalden, Skraup, 



dodecanoic acid 1904) 



Crystine (Wollaston, 1810 ; K. A. H. Morner, 1899) 



" In this table are included all the substances hitherto pre- 

 pared from the proteins, the existence of which is established, 

 with a short reference to their discovery. 1 . . . 



1 This was in 1907. Since that date further progress has been made in 

 building up polypeptide molecules. Among the important steps may be 

 mentioned the introduction of tyrosine groups into the molecule. Tyrosine is of 

 frequent occurrence in natural proteins, and it appears now that the difference 

 between natural and synthetic polypeptides consists less in the number of the 



