THE CULTIVATION OF MICRO-ORGANISMS 



III 



it becomes solidified. Gelatin roll-tubes must be kept in a place 

 so cool that there is no danger of their melting; in handling them 



FIG. 43. Dilution-cultures in Esmarch roll-tubes. In tube i the colonies are 

 very close together; in tube 2 they are somewhat separate; in tube 3 they are well 

 isolated. 



they are to be held near the neck, so that the warmth of the hand 

 may not melt the gelatin. Agar roll- tubes should be kept in a 



