450 CHOLERA 



shaped depression ; below this there is a funnel-shaped area of 

 liquefaction, the fluid being only slightly turbid, but showing at 

 its lower end thick masses of growth of a more or less spiral 

 shape (Fig. 134). The liquefied portion gradually tapers off 

 downwards towards the needle track. (This appearance is, 

 however, in some varieties not produced till much later, especi- 

 ally when the gelatin is very stiff, and, in 

 other varieties which liquefy very slowly, 

 may not be met with at all.) At a later 

 stage, liquefaction spreads and may reach 

 the side of the tube. 



In gelatin plates the colonies are some- 

 what characteristic. They appear as minute 

 whitish points, visible in twenty-four to 

 forty-eight hours, the surface of which, under 

 a low power of the miscroscope, is irregularly 

 granular or furrowed (Fig. 135, A). Lique- 

 faction occurs, and the colony sinks into 

 the small cup formed, the plate then show- 

 ing small sharply-marked rings around the 

 colonies. 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 (Fig. 135, B). 



On the surface of the agar media a thin, 

 almost transparent, layer forms, which pre- 

 sents no special characters. On solidified 

 blood serum the growth has at first the same 

 appearance, but afterwards liquefaction of 



tlle 



spirillum in peptone superficial colonies under a low power are 



gelatin six days' circular discs of brownish-yellow colour, and 



growth. Natural size. more transparent than those of most other 



organisms. On potato at the ordinary 



temperature, growth does not take place, but on incubation 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 



