TESTS FOR THE REDUCTION OF NITRATES 133 



sium persulphate, a condensation of two molecules of indol 

 with the aldehyde group of the para-dimethyl-amido- 

 benzaldehyde, water splitting off. 



Apparatus. Solutions I and II for Ehrlich's test for 

 indol;* two clean 5 c.c. pipettes. 



Culture. Dunham's peptone solution or broth culture 

 of the organism to be tested. 



Method. 1. To about 10 c.c. of the liquid culture 

 add 5 c.c. of solution I, then 5 c.c. of solution II. 



2. Shake the mixture. The reaction may be accelerated 

 by heating. The presence of indol is indicated in a few 

 minutes by a red color which increases in intensity with 

 time. For standard compaiisons, five minutes is taken 

 as the maximum time limit. 



REFERENCES 



BOEHME, A.: Die Anwendung der Ehrlichschen Indol-reaktion fur 



Bakteriologische Zwecke. Cent. f. Bakt. Orig. Bd. 40 (1906), 



pp. 129-133. 

 BESSON: Practical Bacteriology, Microbiology and Serum Therapy 



(1913), p. 374. 



LOHNIS: Laboratory Methods in Agricultural Bacteriology (1913), p. 42. 

 LEWIS, F. C.: On the detection and estimation of bacterial indol and 



observations on intercurrent phenomena. Jour. Path, and Bact., 



Vol. 19 (1915), pp. 429-443. 



EXERCISE 45. TESTS FOR THE REDUCTION OF 

 NITRATES 



The purpose of the exercise is to test the power of an 

 organism to reduce nitrates. 



Apparatus. Sulphanilic acid, nitrite test solution I; 

 a-naphthylamin, nitrite test solution II; Nessler's solution; 

 phenolsulphonic acid. 



Cultures. Seven-day old nitrate peptone solution cul- 

 tures grown at 20 to 25 C., or four-day old nitrate pep- 

 tone solution cultures (pathogenic) grown at 37 C. 



Method. (A) For nitrites: 1. Add 0.1 c.c. each of 

 solutions I and II to each culture to be tested. 

 * See Appendix. 



