BIOLOGICAL PROPERTIES 



493 



Gelatin. Stab culture. After incubating at 20 C. for 20 hours small 

 colonies appear along the line of the stab. A small cup-shaped depression 

 is formed at the surface in which a bubble of air is retained ; 

 liquefaction then increases and progresses in a funnel-shaped 

 manner being more marked at the surface than in the depth, 

 the bubble of air remaining at the surface : about the second 

 to the fourth day the growth is characteristic. The medium 

 is subsequently entirely liquefied. 



Single coloni es. After incubating at 20 C. for about 20 

 hours small whitish points are visible which quickly become 

 irregular-shaped colonies with granular centres surrounded 

 by a bright ring. Liquefaction then commences : a small 

 cup-shaped depression is formed with the colony in the centre 

 from the periphery of which small clumps of vibrios become 

 detached, and the plate is soon completely liquefied. 



Agar. Incubation at 37 C. gives a copious whitish growth 

 which develops rapidly but has no 

 special features. 



Isolated colonies are irregular and 

 greyish : the centres are granular 

 and surrounded by a smooth mar- 

 ginal zone. 



Coagulated serum. The growth on 

 this medium is rapid. The serum 

 is liquefied. 



Pntatn Thp nTinlpra vihrin CTTTW strain). Stab culture 



roiato. LO grows in ge i atin ( 5 days), 



well only on alkaline potato (p. 

 55) ; on this medium a thick clear brown streak is 

 formed. 



Milk. This medium is sometimes coagulated. 

 Koch believed that one of the characteristics of the cholera vibrio was that 

 it did not clot milk. Since then however it has been shown that some 

 varieties of cholera vibrios of the identity of which there can be no doubt 

 produce quite a distinct clot. 



FIG. 240 Vibrio 

 cholerce (Indian 



FIG. 241. Vibrio cholerw 

 (Indian strain). Single colony 

 on gelatin plate, x 60. 



SECTION III. BIOLOGICAL PROPERTIES. 

 1. Vitality and Virulence. 



The cholera vibrio retains its vitality for a long time in artificial culture, 

 provided that the tubes be kept in the dark and be prevented from drying 

 up. Under these conditions agar cultures will be found to be living after 

 5 months. 



The cholera vibrio is very rapidly killed by drying, especially in artificial 

 cultures. 



A temperature of 50-60 C. kills the vibrios in ten minutes : on the other 

 hand very low temperatures ( - 10 C.) have no action on their vitality. 



The vibrio is very susceptible to the action of acids and antiseptics : 

 traces of perchloride of mercury, quinine sulphate, etc., arrest growth in 

 culture. 



Cholera vibrios have been found to be capable of living for from 15-30 

 days in spring water (Strauss and Dubarry). They are destroyed in three or 

 four days in excreta by the action of putrefactive bacteria (Koch). 



In discussing the disease experimentally produced in animals stress has 



