98 SCIENCE- PROGRESS 
separation and identification of the monoamino acids, on the 
other hand, by the older methods was extremely crude, and 
only where a large amount of one or two of the monoamino 
acids was present, was their isolation and characterisation 
carried out. Fischer, by introducing the ester method of sepa- 
rating the monoamino acids from one another, has advanced our 
knowledge of these acids considerably. His method, though 
not yet quantitative, gives us the means of obtaining about 
70 per cent. of the total products. 
In the majority of his experiments Fischer used concentrated 
hydrochloric acid as the hydrolysing agent, in some cases dilute 
sulphuric acid. This is particularly useful when tyrosine and 
diaminotrioxydodecanic acid only require isolation, the best 
results being obtained by boiling the protein for twelve to 
fifteen hours with five to six times its quantity of 25 per cent. 
sulphuric acid. This solution, after filtration and dilution with 
twice its volume of water, is neutralised with baryta, the excess 
of which is removed with sulphuric acid. The solution, after 
thoroughly washing out the precipitate of barium sulphate, is 
concentrated till these acids crystallise out. This method is 
extremely simple, but requires many days to carry out, as the 
filtration and washing out of the barium sulphate is very 
laborious. An improvement has recently been introduced 
by Abderhalden and Teruuchi, who use hydrochloric acid to 
hydrolyse the protein; after removal of the greater quantity 
of hydrochloric acid by evaporation in vacuo, the solution is 
treated with caustic soda in sufficient amount to exactly combine 
with the remainder of the hydrochloric acid, when the tyrosine 
crystallises out. 
In all cases where the separation of tyrosine was not required, 
hydrochloric acid was used as the hydrolysing agent on account 
of its far greater convenience. The protein is covered with three 
times its quantity of concentrated hydrochloric acid in a flask ; 
in a short time the majority of the proteins go into solution if 
the vessel be occasionally shaken, and the hydrolysis is com- 
pleted by boiling the solution under a reflux condenser for five 
or six hours. The solution first becomes dark violet in colour 
and then dark brown; a large proportion of the hydrochloric 
acid escapes as gas, and a solution remains consisting of the 
hydrochlorides of the amino acids in 25 per cent. hydrochloric 
acid. Humin substances and fat-like masses, which separate 
