THE CULTIVATION OF BACTERIA. 97 



The culture-medium in the Petri dish will soon solidify. 

 Petri dishes -of agar should be inverted as soon as the medium 



Fig. 33. — 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. 



is thoroughly solidified, otherwise the water which evaporates 

 7 



