246 INTESTINAL BACTERIA 
According to Mathews cystine goes to cysteine, and then as: 
SH—CH2—CHNH:2 — SHCH2—CH2NH2 — SHCH2—CHs 
Thioethyl amin Ethyl mercaptan 
The action of bacteria and yeast-like fungi has been studied by 
Tanner (1917, 1918). These microorganisms were quite able to split 
hydrogen sulphid from cystine. 
Some of these decomposition products of the amino acids and pro- 
teins may be detected as follows: The solution to be tested may be 
either a filtered bacterial culture or a fecal suspension. 
Indol Determinations. A number of methods have been devised 
for the detection of indole. Most of these yield good results when 
applied to bacteriology. 
Nitroso-indol Nitrate Reaction. Acidify a portion of the substance 
under examination with concentrated nitric acid. The addition of a 
few drops of potassium nitrate will produce a red coloration if indol is 
present. The red compound is nitroso-indol nitrate. 
Nitro-prusside Reaction. Add a few drops of a freshly prepared solu- 
tion of sodium nitro-prusside to a filtered sample. Add sodium hydrox- 
ide and examine for the production of a violet color. This may be 
changed to a blue by the addition of a few cubic centimeters of strong 
acetic acid. 
Ehrlich’s Para-dimethyl Amino Benzaldehyde Test. Add about 
one-third the volume of a 2 per cent solution of para-dimethyl amino 
benzaldehyde in aclohol to the sample under examination. Then 
slowly add dilute hydrochlorine acid until a red color is evident. This 
color may be deepened by the addition of a few drops of sodium nitrite 
solution. 
Bergeim’s (1917) Method for Determination of Fecal Indol. Rub 
30 to 50 gms. of the fresh feces in a mortar with H2O. Transfer to a 
1 liter Kjeldahl flask and add H2O to 400 ¢.c. Add 5 c.c. 10 per cent 
KOH and 2 c.c. paraffine and distill with steam until 500 ¢.c. have been 
obtained, bringing the volume of the fecal suspension down to about 
100 cc. Re-distill with steam after acidifying slightly with HeSOx. or 
else remove the NH3 with permutite. Mix an aliquot of the resulting 
solution (100 ¢.c.) in a 150-c.c. separatory funnel with 1 ¢.c. of a fresh 
2 per cent solution of NaB naphthoquinonesulphonate and 2 c.c. of 
10 per cent KOH. After fifteen minutes extract with CHCls using 
10 and 7 c¢.c. Dilute extract to 15 c.c. and mix. Compare color in the 
colorimeter with that of a standard similarly prepared, using 0.1 mg. 
indol. The error appears to be only—1 per cent. 
