fhe CheMistey. Or THE PROTEINS 119 
acids are removed and the residue treated with ammonia. A 
substance crystallised out, which was found to be identical 
with the diketopiperazine formed from glycine and alanine. 
On hydrolysis it yielded glycine and d-alanine, but whether it 
was glycyl-d-alanine or d-alanylglycine could not be exactly 
determined, but most likely it is the anhydride of glycyl-d-alanine, 
as the product is not hydrolysed by trypsin. 
At the same time another dipeptide, glycyl-l-tyrosine, was 
mentioned, but its constitution was only determined later. Its 
anhydride has been found to be identical with the synthetical 
glycyl-l-tyrosine anhydride, and it occurred mixed with the 
glycyl-d-alanine anhydride obtained in the above manner. 
Glycine and ]-tyrosine resulted on hydrolysis. 
By the same method, the anhydride of glycine and leucine 
has been prepared from elastin; it corresponded exactly to 
glycyl-l-leucine anhydride. To these three dipeptides, a fourth 
must be added. It is described by Levene and Beatty as 
prolylglycine anhydride and was obtained from gelatine. 
Further, a crystalline substance, probably a dipeptide, which 
gives proline and phenylalanine on hydrolysis, has been isolated 
from the products of the acid hydrolysis of ghadin by Osborne 
and Clapp. 
The protones, which are obtained from the protamines by 
digestion, have a molecular weight of about 420. Just as in 
the protamines, eight-ninths of their nitrogen is in the form of 
arginine. Kossel therefore believes that they are mixtures of 
tripeptides, such as diarginylalanine, diarginylserine, etc., which 
have the molecular weights of 401 and 417 respectively. 
Leucinimide, leucylleucine anhydride, described many years 
ago by Bopp, has not yet again been isolated, and, according to 
Fischer, its existence is doubtful. 
The work of Emil Fischer emphasises most strongly the 
importance of the knowledge of organic chemistry to physio- 
logical chemistry, in which branch the proteins are generally 
studied. There is in reality no absolute difference between the 
two subjects; physiological chemistry deals with the question 
how these substances are made, and what changes they undergo, 
in nature, whereas organic chemistry treats of the changes they 
can be made to undergo by various chemical means in the 
laboratory, and how they can be ‘synthesised. Synthesis also 
occurs in nature, but whether it proceeds in a manner similar to 
