CULTIVATION 



465 



what with different varieties, and also on different sorts of 

 potatoes. 



In bouillon with alkaline reaction the organism grows very 

 readily, there occurring in twelve hours at 37° C. a general 

 turbidity, while the surface shows a thin pellicle composed of 

 spirilla in a very actively motile condition. Growth takes place 

 under the same conditions equally rapidly in peptone solution 

 (1 per cent, with -5 per cent, sodium chloride added). It usually 

 produces acid, without gas formation, from glucose, saccharose, 

 mannite, and maltose ; fermentation of lactose, with acid pro- 

 duction, occurs late, namely, after two to three days. 



In milk also the organism grows well, and produces no 



Fig. 139. — Colonies of the cholera spirillum on a gelatin plate — 

 three days' growth. A shows the granular surface, liquefaction just 

 commencing ; in B liquefaction is well marked. 



coagulation nor any change in its appearance, at least for several 

 days. 



On all the media the growth of the cholera spirillum is a 

 relatively rapid one, and especially is this the case in peptone 

 solution and in bouillon, a circumstance of importance in relation 

 to its separation in cases of cholera (vide p. 475). 



The cholera organism is one which grows much more rapidly 

 in the presence of oxygen than in anaerobic conditions ; in the 

 complete exclusion of oxygen very little growth occurs. 



Cholera-Red Reaction. — This is always given by a true 

 cholera spirillum, and though the reaction is not peculiar to it, 

 the number of organisms which give the reaction under the 

 conditions mentioned are comparatively few. The test is made 

 by adding a few drops of pure sulphuric acid to a culture in 

 bouillon or in peptone solution (1 per cent.) which has been 

 incubated for twenty-four hours at 37° C. ; in the case of the 

 cholera spirillum a reddish-pink colour is produced. This is clue 



3° 



