96 SCIENCESPROGRESS 
with ammonia gave two oxypyrrolidine carboxylic acids. One 
of these is probably the inactive form of the optically active 
oxyproline isolated by Fischer from the products of hydrolysis 
of gelatine. 
Tryptophane was first isolated by Hopkins and Cole and 
supposed to be either scatoleaminoacetic acid or indoleamino- 
propionic acid. The work of Ellinger during the last few years 
points to its having the latter constitution. 
The last amino acid which we have to consider is cystine. 
Our knowledge of this compound rests chiefly upon the work of 
Morner and of Friedmann, who showed that on oxidation and 
loss of carbon dioxide it yielded taurine. Together with Suzuki, 
Fischer has prepared several of its derivatives and has compared 
the cystine as obtained from proteins on hydrolysis with that 
from cystine calculi. Contrary to the statement of Neuberg and 
Mayer, the two products were found to be identical, and 
Rothera’s work in Cambridge was thus confirmed. At present, 
therefore, only the one cystine is a decomposition product of 
proteins, though the isomeric, isocystine, has been synthesised. 
Finally, diaminotrioxydodecanic acid, which has only recently 
been isolated by Fischer and Abderhalden from the products 
of the hydrolysis of proteins, has not yet been synthesised, and 
its exact constitution is unknown. 
Not only has Fischer synthesised the amino acids, but he has 
also prepared a large number of derivatives, in addition to the 
benzoyl and formyl compounds, whereby their isolation, purifi- 
cation, and recognition can be determined. The benzenesulpho 
derivatives, and especially the 6-naphthalene sulpho derivatives, 
which are obtained by shaking an alkaline solution of the amino 
acid with the sulphochloride, are very useful for separating 
amino acids from very dilute or impure solutions. The latter 
derivative forms compounds with all the amino acids and with 
many of the polypeptides. It has been used by many workers 
to isolate amino acids from urine and other secretions (Samuely, 
Abderhalden and Schittenhelm, Lipstein, Emden and Reese). 
The combination of the amino acids with phenylisocyanate 
in alkaline solution to form phenylureido acids, and the action 
of hydrochloric acid on these compounds to form their anhy- 
drides, z.e. derivatives of hydantoine, first observed by Mouney- 
rat, has been much used to characterise the amino acids on 
account of the ease of crystallisation and sharp melting points 
