412 CHOLERA. 



Under the microscope the outer margin of the cup is circular 

 and sharply marked. Within the cup the liquefied portion forms 

 a ring which has a more or less granular appearance, whilst the 



mass of growth in the 

 centre is irregular and 

 often broken up at its 

 margins. The growth 

 of the colonies in gela- 

 tin plates constitutes 

 one of the most impor- 

 tant means of distin- 



FIG. 142. Colonies of the cholera spirillum in a rruishing" the cholera 

 gelatin plate ; three days' growth. A shows the granu- . . 



lar surface, liquefaction just commencing; in B, lique- Spirillum from Other 



faction is well marked. organisms. 



On the surface of the agar media a thin semi-transparent 

 layer forms, which presents no special characters. On solidified 

 blood serum the growth has at first the same appearance, but 

 afterwards liquefaction of the medium occurs. On agar plates 

 the superficial colonies under a low power are circular discs of 

 brownish-yellow colour, and more transparent than those of most 

 other organisms. Qi\ potato at the ordinary temperature, growth 

 does not take place, but when it is incubated at a temperature 

 of from 30 to 37 C, a moist layer appears, which assumes a 

 dirty brown colour somewhat like that of the glanders bacillus ; 

 the appearance, however, varies somewhat in 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 tur- 

 bidity, 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 (i per 

 cent with .5 per cent sodium chloride added). 



In milk also the organism grows well and produces no coagu- 

 lation 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 the peptone 

 solution named and in bouillon, a circumstance of importance in 

 relation to its separation in cases of cholera (vide p. 426). 



Cholera-red Reaction. This is one of the most important 

 tests in the diagnosis of the cholera organism. It is always 



