CULTIVATION 



463 



a whitish line appears along the needle track, at the upper part 

 of which liquefaction commences, and as evaporation quickly 

 occurs, a small bell-shaped depression forms, which gives the 

 appearance of an air-bubble. On the fourth or fifth day we get 

 the following appearance : There is at the surface the bubble- 

 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. 138). The liquefied portion 

 gradually tapers off downwards towards the 

 needle track. (This appearance is, how- 

 ever, 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 liquefaction 

 spreads and may reach the side of the tube. 

 When the organism is sub-cultured over a 

 long period of time, it may lose to a large 

 extent the property of liquefying gelatin. 



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. 139, 

 A). 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 lique- FIG. 138. Puncture 

 fled portion form, a ring which has a more $rfS5m to'$S 

 or less granular appearance, whilst the mass gelatin six days' 

 of growth in the centre is irregular and often growth. Natural size, 

 broken up at its margins (Fig. 139, B). 



On the surface of agar media a thin, almost 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. On potato at the ordinary temperature, 



