128 



which growth was prompt and very copious, the paper browned slowh^ 

 and the substratum also linally changed to brown. In a tube of radish 

 there was no visible browning of the paper up to the fourteenth day 

 of exposure, and on the same date there was only the merest trace of 

 browning on the lower margin of the strip in the tube of yellow globe 

 turnip. On this date there was an equally good growth in the 2 tubes, 

 but there was no stain of the substratum in the tube of radish, while 

 there was a distinct browning of the whole substratum in the tube of 

 turnip. 



Ps. stewarti grayed potato cylinders, but did not brown the lead 

 paper (9 days' exposure). On rutabaga and yellow globe turnip it 

 neither browned the paper nor stained the substratum {6-1: days). Also, 

 on white radish in 64 days the substratum was not stained, but no test 

 was made for HgS. 



Bacillus coli and an undetermined white organism (received as B. 

 coll from the bacteriological laboratory of the Army Medical Museum), 

 grayed potato cylinders promptly, but there was no browning of the 

 lead acetate paper in 58 days. 



For behavior of Ps. phaseoli see The Brown Pigment. 



FORMATION OF INDOL. 



The pink or red indol reaction was obtained with Ps. liyacintld by 

 adding sulphuric acid and sodium nitrite to cultures in Dunham's solu- 

 tion, in peptonized sugar-free beef broth, and in peptonized Uschinsky's 

 solution. My practice was to add to the culture 15 drops of a mixture 

 of sulphuric acid and water (2 acid, 1 water), and then 1 c. c. of distilled 

 water containing 0. 1 per cent sodium nitrite. If the color did not come 

 at once, or within a few minutes (which was frequently the case), the 

 tubes were plunged into water at 75^ to 80° C. for 5 minutes, during 

 which the color appeared. The color was a distinct red or pink. Unin- 

 oculated tubes tested at the same time gave no such reaction. Cultures 

 of various ages were used, but none less than 3 weeks old. Old cul- 

 tures must be used to obtain a distinct reaction, and in none was the 

 color more than one-quarter as deep as that in corresponding tubes of 

 Bacillus coli. In no case could any indol reaction be obtained from 

 culture fluids which did not contain peptone. The same result was 

 obtained with B. coli and a half dozen other organisms used for com- 

 parison. The presence in the culture fluid of peptone (using this term 

 in the commercial sense) appears to be necessary for the production of 

 indol. 



The indol reaction was also obtained from cultures of Ps. campestris^ 

 Ps. steioarti^ and Bacillus amylovorus. 



