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:\IICRO-ORGAXISMS AND DISEASE [chap. 



the whole growth appears more white in reflected hght. 

 After 3-4 days the band has spread over the greater part of 

 the surface of the gelatine, but is still dry, filmy, crenate, 

 and irregular in the marginal part; the whole band examined 

 under a glass appears more or less homogeneous. 



When ordinary nutrient gelatine is inoculated from a 

 culture, then melted and shaken and allowed to set again. 



Fig. 63 — I.Mi'Ki;ssii")N' Sl'ECI^rI^^- of the Marginal Part of a Colony 

 Uacillls CoLi ; .most uf the Bacilli are C\li.ni)kilal. 



and incubated, it will be found after 24-36 hours that this 

 shake culture is permeated by minute spherical colonies in all 

 its depth, and in connection with each colony is a spherical or 

 lenticular gas bubble (methan gas) ; this gives to the culture a 

 very characteristic aspect ; the same is observed if, instead of 

 ordinary nutrient gelatine, grape-sugar gelatine is used for 

 the shake culture. In gelatine stab culture the stab becomes 

 on incubation marked as a row or rows of minute dots 



