18 



It does not seem to me that the distinct difference between the 

 indol and cholera-red reactions has been sufficiently emphasized 

 in the past. By reference to the before-mentioned publication it 

 will be seen that I did not fully appreciate this difference myself 

 for reasons which will be evident. Salkowski and Nencki^ 

 mistook the purple-colored indol reaction for the cholera red, and 

 although Petri and Bleisch undoubtedly produced the cholera-red 

 reaction, they do not dwell on the difference between it find the 

 indol reaction. KoUe^ says that "on adding small quantities 

 of concentrated, chemically pure sulphuric or hydrochloric acid 

 to bouillon or peptone cultures of cholera vibrios a violet or 

 burgund^'-wine-red color appears as was shown by Poehl and later 

 by Bujwid and Dunham." Now there is a very distinct difference 

 between the violet or purple colored indol reaction and the 

 vermilion-colored cholera-red reaction when these tests are per- 

 formed under carefully controlled conditions; and since both 

 tests are of value in the differentiation of species, it seems advis- 

 able to define further the conditions under which they must be 

 performed. 



Further, my experiments have convinced me that the cholera 

 spirillum does not produce nitrites in Dunham's peptone solution, 

 made from Witte's "peptone" dialyzed free from nitrites, and 

 that the apparent production of nitrites can l)e explained liy the 

 testing of uninoculated controls. 



(I) RESULTS OF A SEARCH FOR NITRATES AND NITRITES 

 IN SOME INGREDIENTS USED IN PREPARING MEDIA.'' 



In testing for nitrogen, as nitrites, the naphthylamine-hydro- 

 chloride and sulphanilic-acid test was used in the manner usually 

 emploj'ed in Nesslerizing for ammonia, excepting that for purposes 

 of comparison the reactions were performed in culture test tubes. 

 In practice 1 culiic centimeter of each test solution was added to 

 10 cubic centimeters of the fluid to be tested. Where nitrates were 

 sought for, the phenol-sulphonic-acid test was used and the reac- 

 tions performed in 3-inch porcelain evaporating dishes. 



The preliminary examination of a number of bottles of distilled 



' Vide the article by M. Bleisch, loc. cit. 



^ Handbuch der Puthogenen MikTOorganismen, Kolle u. Woftserrnan, 1903, 3, 21. 

 'I am indebted to Mr. C. L. Bliss, physiological chemist of the Bureau, for 

 valuable advice during the course of the experiments. 



