APPEARANCES OF CULTURES 



323 



film or pellicle, with irregularly wavy margin (Fig. 113, A). It 

 is semi-transparent and of bluish-white colour. Ultimately this 

 surface growth may reach the wall of the tube. Not infrequently, 

 however, the surface growth is not well marked. Along the 

 stab there is an opaque whitish line of growth, of finely nodose 

 appearance. There is no liquefaction of the medium, and no 

 formation of gas. In stroke cultures there is a thin bluish-white 



ABC 

 FIG. 113. 



A. Stab culture of the typhoid bacillus in gelatin, five days' growth. 



B. Stroke culture of the typhoid bacillus on gelatin, six days' growth. 



C. Stab culture of the bacillus coli in gelatin, nine days' growth ; the gelatin is split 

 in its lower part owing to the formation of gas. 



film, but it does not spread to such an extent as in the case of 

 the surface growth of a stab culture (Fig. 113, B). In gelatin 

 plates also the superficial and deep colonies present correspond- 

 ing differences. The former are delicate semi-transparent films, 

 with wavy margin, and are much larger than the colonies in the 

 substance, which appear as small round points (Fig. 114). These 

 appearances, which are well seen on the third or fourth day, 

 resemble those seen in agar plates, as already described in the 

 method of isolation ; but on gelatin the surface colonies are 



