CULTIVATION 



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appearance : there is at the surface the bubble -shaped de- 

 pression ; 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. 137). 

 The liquefied portion gradually tapers off downwards towards the 

 needle track. (This appearance is, however, in some varieties not 

 produced till much later, especially 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, lique- 

 faction 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 microscope, is irregularly granular 

 or furrowed (Fig. 138, A), and later has an 

 appearance which has been compared to 

 fragments of broken glass. Liquefaction 

 occurs, and the colony sinks into the small 

 cup formed, the plate then showing 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. 138, B). The growth of the 

 colonies in gelatin plates constitutes one of 

 the most important means of distinguishing 

 the cholera spirillum from other organisms. 



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 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. 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 



FIG. 137. Puncture 

 culture of the cholera 

 spirillum in peptone 

 gelatin six days' 

 growth. Natural size. 



