CULTIVATION OF BACTERIA 



33 



dishes, called 'Tetri dishes" or ''plates." This ''plat- 

 ing" method is extensively used to determine the 

 number of living bacteria in milk and in water. 



Fig. 15. — Pouring plates (Eyre). 



Plate cultures are also employed in isolating bacteria 

 in pure cultures. Without entering into the details of 



Fig. 16. — Appearance of colonies on gelatin in Petri dish (Williams). 



the method, we may say that in general it consists in 

 the preparation of a number of plate cultures from the 

 material to be examined, selecting the plate on which 



