26 



formed, and agree with Petri, who considered the existence of such 

 a nitrifying power as unproved as well as improbable. 



(4) The vermilion-colored "cholera-red reaction" must be 

 distinguished from the purple-colored "indol reaction." 



(5) The production of "cholera-red,". by the cholera spirillum 

 or B. coll, takes place only, under the conditions of these experi- 

 ments, during the reduction of a trace of nitrate, and when formed 

 is demonstrable as such, whether pure sulphuric acid alone or 

 sulphuric acid and nitrite are added, although an excess of nitrite 

 furnishes enough nitrous acid to obscure the reaction. 



(6) The growth of B. coll or the cholera spirillum in the presence 

 of sufficient nitrite to yield the indol reaction on the addition of a 

 pure acid alone does not influence the character of the indol 

 formed, but if a considerable amount of nitrite be present in the 

 medium the further addition of nitrite yields enough nitrous acid 

 to obscure the indol reaction. 



(7) The cholera-red reaction is not specific. 



(8) It is recommended that media used in testing for the 

 production of indol or cholera red be examined for nitrates and 

 nitrites before use. 



o 



