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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
fatty acid). This reaction probably consists in the hydrolysis of 
the amino acid into a hydroxy acid and Nil,, then a reduction 
of the hydroxy acid to the fatty acid. The formation of valeric 
acid from valine may be written 
<CH,) 2 oh ch NH 2 COOH — > (CH.), ch choh COOH + NH :{ — > 
valine hydroxy isovaleric acid 
(CH 3 ) 2 CH CPE COOH 
isovaleric acid 
However, the bacterial action does not usually stop at this 
point. The acid may undergo oxidation to the next lower mem- 
ber of the series, and this in turn may meet the same fate, until 
finally only the cyclic nucleus is left, as in the ease of tyrosine 
and tryptophan. Tyrosine and tryptophan present a complete 
series of degradation products, all the intermediate stages hav- 
ing been identified. Thus, 
HO .C«H 4 .CH 2 CH .NHa .COOH > HO .C«H 4 ,OH»CH 2 COOH — > 
tyrosine p-hydroxyphenylpropionic acid 
HO . Ci;H 4 .CHo .COOH — > HO .CHECH, — > HO .C 6 H 3 
p-hydroxyphenylacetic acid p-cresol phenol 
The behavior of micro-organisms toward the optical isomers 
of amino acids is a problem of considerable interest. All of the 
amino acids under consideration, with the exception of glycine, 
contain at least one asymmetric carbon atom. They are, there- 
fore, capable of existing in an isomeric form with opposite op- 
tical properties. The naturally occurring form is readily at- 
tacked by micro-organisms, whereas its optical isomer remains 
unaltered. 
The racemic mixture of the two forms can therefore be sepa- 
rated, one form being destroyed and the other remaining in- 
tact. This specific behavior is made use of in preparing the isomer 
of an optically active substance, the latter being first racemized 
by heating with a base, and added to a suitable culture medium, 
upon which the desired organism is then inoculated. There 
are, however, three exceptions to the phenomenon of asymmet- 
ric utilization of amino acids by organisms. Aspartic acid, tyro- 
sine and proline are broken down with equal readiness when 
present in either optical form. The phenomenon of specific utili- 
zation by micro-organisms is manifested not only toward optical 
or geometrical isomerides but also toward isomerides charac- 
terized by the location of the amino group which must be attached 
