454 MICRO-ORGANISMS AND DISEASE [chap. 



cholera has produced already in twenty-four hours a con- 

 spicuous film. 



If to a peptone salt culture of pure cholera vibrio, as 

 soon as it shows turbidity (no matter whether incubated at 

 20° C. or at 37°), a few drops oi pure sulphuric acid are 

 added, as was mentioned on a former page, a distinct 

 rose-red tint, cholera red, is produced ; a peptone salt culture 

 of vibrio Finkler which in order to produce turbidity had 

 been incubated at 20° C. — it does not become turbid at 

 37"= C. — treated with a few drops of pure sulphuric acid gives 

 no cholera red reaction. The assertions to the contrary are 

 based on the sulphuric acid used not being pure but con- 

 taining nitrites ; with such impure sulphuric acid also in a 

 peptone culture of proteus vulgaris a red reaction is 

 obtainable. 



Another point in this connection worth mentioning is 

 that for the demonstration of the pure cholera red reaction 

 the peptone used for peptone salt culture ought to be pure 

 and free from nitrites. Pestana of Lisbon, who isolated 

 from the intestinal discharges of cases of cholerine that 

 occurred in epidemic form in Lisbon in 1894 a vibrio (see 

 below), has shown that a culture of it in peptone salt, when 

 the peptone used was free from nitrites, gives no cholera red 

 reaction, but a culture of it in peptone salt made with 

 nitrite-containing peptone gives a faint but distinct cholera 

 red reaction. 



Soon after Koch's discovery Deneke ^ isolated from stale 

 cheese a spirillum — spirillum tyrogenum, which in morpho- 

 logical and cultural respects bore a very great resemblance 

 to Koch's cholera vibrio, in fact, looked at in the light of 

 the present knowledge of different varieties of cholera vibrio, 

 cannot be distinguished from this latter. In size, shape, 

 ^ Deutsche Mcdicin. Wochenschrifl , 1885, No. 3. 



