104 SCIENCE PROGRESS 
remainder is only obtained after the removal of the glutamic acid 
as hydrochloride. 
The ester method has not led to the discovery of a large 
number of new amino acids; to this category proline and 
oxyproline belong. The possibility that proline is a secondary 
product formed by the action of acid on another amino acid 
is negatived by the fact that it results when the proteins are 
hydrolysed by alkali. The great use of the ester method has 
been to separate the amino acids, and to determine their great 
variety in all the proteins; formerly, only those existing in 
large amounts, such as tyrosine, leucine, aspartic acid, were 
isolated. The ester method also gives larger amounts. Alanine, 
serine, and phenylalanine, which was only once isolated by 
Schulze from plant proteins, were seldom found, but now their 
universal presence in all proteins is definitely established. 
Phenylalanine, in its distribution, is the chief aromatic com- 
pound, since tyrosine does not occur in all proteins, and it 
often exceeds in amount that of tyrosine when both exist in the 
same protein. 
These results can be seen at a glance by referring to the 
following table, which also shows thé various amounts of 
individual amino acids in percentages, as they result on the 
hydrolysis of proteins: 
ees Caseinogen. | Gelatine. | Silk fibrin. | Egg-albumin. 
Glycine . : ane ae 16°5 36°0 R. 
Alanine . : : 4°2 o'9 08 21°0 2A 
Valine . ; ; present 1'O 1‘ ses eee 
Leucine . 3 : 29'0 10°5 21 LG 6'1 
Proline . , 23 ci! 5°2 present 2a 
Phenylalanine 4°2 3°2 o'4 is 4°4 
Glutamic acid 7 11°O o°9 ts Sie) 
Aspartic acid . 4°4 ig o'6 present 1°5 
Cystine . 03 0°06 oes = o'2 
Serine o°6 0°23 o'4 1°6 mA 
Tyrosine 15 4°5 ae 10°5 Eis 
Lysine 43 58 Aa present 
Arginine 5°4 48 7°6 sme) 
Histidine 11/0 2°6 o°4 present 
Oxyproline ‘ ae oi. 30 ae Ree 
Tryptophane . : es vad aoe ae present 
Not only has Fischer hydrolysed proteins by acids and by 
alkali, but also by the enzymes pepsin and trypsin. The latter 
gives essentially the same products as acids, but its action is 
