424 MICRO-ORGANISMS AND DISEASE [chap. 



rounded or knobbed outline, assuming as growth goes on, 

 i.e., after some days, a slight brownish tint. 



On boiled potato the comma bacilli grow only at tem- 

 peratures above 25° C. ; at 36° they form after a few days a 

 thick, smeary, brown film. In some cases the growth is 

 a transparent film, in others no growth takes place on 

 potato. Comma bacilli grow well and rapidly, if mucus 

 flakes of a cholera intestine containing numerous comma 

 bacilli are placed on linen kept damp. After twenty- 

 four hours the comma bacilli have increased to an enormous 

 extent, almost to the exclusion of other bacteria originally 

 present, provided these were at the outset less numerous 

 than the comma bacilli. 



Cholera vibrios show rapid growth at 37° C. on solidified 

 blood-serum, which becomes liquefied by the growth. 



In cultivations of the comma bacilli one meets with 

 forms which in so far differ from the typical curved, 

 cylindrical vibrios, as they are much thicker, plano-convex, 

 or bi-convex, or even approaching the spherical shape with 

 a clear vacuole in the middle. In well-stained and well- 

 washed specimens also the most typical comma bacilli show 

 within a sheath the protoplasm collected at the ends — as a 

 granule at each end — whereas the middle part remains 

 clear. The above atypical forms are merely a further develop- 

 ment of their normal constitution, being derived from 

 them by enlargement of the central clear space or vacuole. 

 Such atypical forms are to be met with in all cultures ; 

 they are as actively motile as the typical commas ; their 

 number, however, varies greatly with the character of the 

 culture. If comma bacilli, originally derived from the 

 cholera intestine, are carried through many successive sub- 

 cultures in gelatine, say one or two dozen, the number of 

 such atypical bi-convex or spherical forms is found larger. 



