AMINO ACIDS AND MICRO-ORGANISMS 
543 
to Pasteur that these by-products, amounting to only 5 per cent 
of the original sugar, might possibly not have their origin di- 
rectly in the sugar. It remained for Buchner nearly forty 
years later to prove that the fermentation of pure sugar by a 
cell-free extract of yeast gave rise to no succinic acid or fusel 
oil whatever. 
In general it may be said that the action of yeast upon a 
naturally occurring “-amino acid is to add a molecule of water, 
then remove a molecule each of ammonia and C0 2 . The am- 
monia is then utilized for the building up of new protein and 
the remainder of the original molecule cast aside as useless in 
the form of an alcohol of the same chemical structure as the 
amino acid but with one less carbon atom. 
Many investigations dealing with bacterial decomposition of 
proteins are recorded in the literature. Although some of the 
end-products identified in such studies can be traced with more 
or less certainty to a particular amino acid, the problem is 
much more intricate, and therefore the present discussion will 
be confined to studies upon individual amino acids where the 
latter were introduced into a medium freh from other sources 
of nitrogen. 
BACTERIA. 
Turning now to the bacterial decomposition products of amino 
acids, we find the problem somewhat more complex. An examina- 
tion of the table will, however, reveal two predominating types 
of products, viz., amines and fatty acids, both retaining the 
cyclic nucleus of the original amino acid. Out of the fifteen 
amino acids on which data are available at least eight are known 
to give rise to amines, by the simple loss of C0 2 from the car- 
boxyl group. The two dibasic acids, aspartic and glutamic, lose 
the carboxyl adjacent to the amino group but retain the other 
carboxyl, the product being an ^-amino acid. This reaction is 
entirely analogous to that whereby the monobasic amino acids 
are converted into an alkylamine. Taking valine as an illustra- 
tion the reaction may be written 
(ch 3 ) 2 oh ch nh> cooh — > (ch 2 ) 2 ch cm nh 2 + co 2 
isobutylamine 
Out of these same fifteen amino acids, twelve are known to 
give rise to fatty acids (or the corresponding aryl-substituted 
