VIBRIO CHOLEEM 359 



(e) According to investigations by Palermo, cholera vibrios in 

 bouillon are robbed of their virulence, but not killed in three to four 

 hours by sunlight, and in six to seven hours become non-motile. 



Chemical Activities. — 



(a) Chromogenesis : Slight upon potato only. For chol- 

 era-red reaction see below (54, iv). 



(6) Odoriferous and gustative substances: The disagree- 

 able odor of cholera bouillon cultures, which is difficult 

 to describe, was pointed out by Laser as of diagnostic 

 value, but it is not sufficiently specific. 



(c) Formation of gas and acids from carbohydrates : Dex- 

 trorotatory lactic acid is formed in abundance from sugar 

 (grape-, cane-, and milk-sugar) without perceptible pro- 

 duction of gas (Kuprianow, A. H. xix, 282). In 10 c.c. 

 of litmus milk the cholera vibrio forms a blue pellicle on 

 top, the following layer is red, the deepest part is decolor- 

 ized (reduction); thus the formation of alkali is favored 

 by the entrance of oxygen, and the fermentation of sugar 

 and formation of acid by anaerobiosis (Hellin). 



(d) Production of ferments: Besides bacteriotrypsin, 

 some invertin; also, according to Sclavo, rennet ferment. 



(e) H 2 S : In peptone bouillon rather abundant. (See 

 egg culture, p. 357. ) 



(/) Phosphorescence: According to the statements of 

 Rumpel, two cholera cultures ( ' ' Oergel ' ' and ' ' Elwers ' ' ) 

 were photogenic. R. Pfeiffer assumes that there is here 

 a mistake, and denies that these photogenic cultures 

 belong to cholera, basing his conclusion upon his immun- 

 ity reaction described below (p. 373). It is also consid- 

 ered by most authors — for example, Dunbar — to be a 

 photogenic vibrio from water, etc., and not a cholera 

 vibrio at all. But recently Weleminsky, in Hiippe's 

 institute, has observed two cultures of cholera vibrios 

 become photogenic after passage through the body of 

 pigeons, which were not so previously (C. B. xvm, 285). 



(g) Indol : Usually abundant production of indol upon 

 nutrient media containing albumin or peptone. Accord- 

 ing to the number introduced, sufficient indol for demon- 

 stration is formed in peptone-chlorid of sodium solution 

 in three to six or nine to twelve hours. Since simultane- 

 ously, from the small amount of nitrate contained in the 



