Here an iinnicdiatc and distinct cholera-nMl reaction was not 

 olitained nntil tlie ortranisni had grown for three days at 30° to 37°. 

 This experiment (wliich is one of a number) also shows that, 

 when growth takes place in the presence of 0.01 per cent sodium 

 nitrate, even if a trace of nitrite be also originally present, some- 

 thing (an oxidation product of indol?) is ])roduced which is 

 demonstrable as "cholera red,"^ whether sulphuric acid alone or 

 sulphuric acid and nitrite are added subseciuently, though such a 

 further addition of nitrite may obscure the reaction. 



On the other hand, a few days' growth in the presence of suffi- 

 cient nitrite to yield the indol reaction does not influence the 

 character of the indol formed; but if a consideral)le amount of 

 nitrite be present in the medium, the further addition of nitrite 

 yields enough nitrous acid to ol:)SCUre the indol" reaction. 



SUMMARY AND CONCLUSIONS. 



(1) Nitrites, and prolxal)ly nitrates also, may gain entrance to 

 artificial media from various sources — certain waters, "peptones," 

 and filter papers — yielding distinct reactions for nitrites with 

 naphthylamine hydrochloride and sulphanilic acid. 



(2) A sufficient quantity of nitrites may be further absorbed, in 

 a few days, from the laboratory atmosphere, to yield a distinct 

 indol reaction upon the addition of 0.5 cubic centimeter of chem- 

 ically i)ure sulphuric acid to, for example, a culture of B. coli 577 

 grown for twenty-four hours at 36° to 37° in 10 cubic centimeters 

 of Dunham's peptone solution, which originally contained insuffi- 

 cient nitrite to yield such a reaction. 



(3) The cholera spirillum does not produce nitrites in nitrate 

 and nitrite-free "peptone" solution, prepared from Witte's 

 ••pe|)tone" dialyzed free from nitrites; and when nitrites are 

 apparently formed their presence may be explained l)y the simul- 

 taneous testing of uninoculated controls. In this I disagree with 

 lUeisch, who believed that small quantities of nitrites could be 



' Acconling to Kolle (loc. cit. ) "cholera red" was isolated in a pure state 

 liy Brieger, who considered the cholera-red reaction a.s nothing more than 

 the nitroso-indol reaction — the nitrous acid set I'ree combining with (he 

 indol to produce a new substance, the cholera red. Brieger's original articles 

 ( Dt'iil. Mid. Wodi. 1887, Nos. 15 anrl 22), while ordered for the library, are 

 not within reach, so I can not discuss this point. 



