KOCH PLATE AND PETRI DISH CULTURES. 



67 



made in a draft or near an open window. They should be 

 done as quickly as possible. 



Koch plate culture : This method requires considerable 

 apparatus, and on the whole is not so satisfactory as the two 



FIG. 21. 



Levelling-tripod with glass chamber for plates. 



other methods. The cultures are made on clean smooth glass 

 plates, which are placed on a levelling apparatus under a 

 sterile glass chamber (Fig. 21). The technique is the same as 

 for the Petri dish culture. 



FIG. 22. 



Petri dish. 



Petri dish culture : This is the method commonly used. 

 It is easily done and gives the most satisfactory results in 

 every way. Petri dishes (Fig. 22) are glass dishes, about 

 four inches in diameter and about | inch in depth, provided 



