98 VETERINARY BACTERIOLOGY 



of free oxygen, can reduce certain chemicals, evidently securing 

 oxygen for growth processes by this means. Litmus, methylene- 

 blue, and other pigments may be decolorized. Nitrates are 

 frequently reduced to nitrites. For this determination a broth 

 made from 0.1 per cent, peptone and 0.02 per cent, potassium 

 nitrate is inoculated and incubated for four days. It is then 

 tested by the following reagent for the presence of nitrites: 



a. 5 N acetic acid ............................ 1000 c.c. 



Sulphanilic acid ........................... 8 gm. 



b. 5 N acetic acid ............................ 1000 c.c. 



Alpha-amidonaphthylene ................... 5 gm. 



Add 2 c.c. of each solution to the tube to be tested. A red or 

 rose color will indicate the presence of nitrite. A control in check 

 tubes of uninoculated broth should always be tested at the same 

 time. 



In some cases denitrification goes still further and the nitrogen 

 is liberated in the free state. 



Other reduction processes have been described. Among the 

 more important are the reduction of sulphates to sulphids, and of 

 chlorates to chlorites. 



Indol Production. Indol is one of the products of protein 

 decomposition formed by bacterial action. It is of importance 

 principally because it may be demonstrated readily and because 

 of the economic importance of some of the bacteria which produce 

 it. It is not formed in the presence of sugars. Dunham's solu- 

 tion is inoculated with the organism to be tested and incubated 

 for several days. To the tube are added a few drops of concentrated 

 sulphuric acid and a cubic centimeter of a 0.1 per cent, solution 

 of sodium nitrite. The sulphuric acid decomposes the nitrite, 

 freeing nitrous acid, which unites with the indol to form a bright 

 red compound known as nitrosoindol. The appearance of this 

 characteristic red color is evidence, therefore, of indol production. 

 Indol is an organic compound of the empirical formula, C 8 H 7 N, 

 and the structural formula 



It is one of the products formed in intestinal putrefaction, and 

 is the principal product which gives rise, under these conditions, 

 to the characteristic " fecal " odor. 



