AMINO ACIDS AND MICRO-ORGANISMS. 
ARTHUR W. DOX. 
The study of amino acids has come to be recognized during re- 
cent years as a subject of tremendous importance, on account of 
its fundamental relation to the problems of human and animal 
nutrition. Not many years, since, all proteins were thought to 
be of equal nutritive value. Now we know that many of the 
proteins are deficient in one or more amino acids, and cannot 
support life and growth unless supplemented by other proteins 
which make up the deficiency. And from a study of the pro- 
teins with reference to their amino acid make-up, the study of 
the amino acids themselves began to occupy the attention of 
chemists. Thus after the chemist had taken the protein molecule 
apart and identified the various amino acids of which it was 
composed, he undertook to synthesize these amino acids from 
simple substances, to separate the synthetic products into their 
optically active components, prepare numerous derivatives, and 
finally to study their behavior toward biological processes of 
both animal and vegetable nature. 
The fact that amino acids play an important part in the phe- 
nomenon of alcoholic fermentation was not known in the time 
of Pasteur. It may safely be said, however, that Pasteur’s ob- 
servations regarding the constant occurrence of certain sub- 
stances in small amounts as by-products of fermentation was the 
incentive which prompted further research in this important 
field by subsequent investigators. 
The disintegration products of amino acids through the in- 
fluence of micro-organisms have an important relation to animal 
nutrition. Micro-organisms may produce profound changes in 
the protein constituents of food, either before or after ingestion. 
These changes have been variously termed ripening, fermenta- 
tion and putrefaction, according to their nature and extent. The 
ripening of cheese consists largely in the disintegration of the 
protein and of amino acids comprising it, and even here no sharp 
line of distinction can be drawn between ripening proper and 
putrefaction, the difference being mainly a matter of the olfac- 
tory and gustatory education of the individual. Fermentation 
