66 



ESSENTIALS OF BACTERIOLOGY 



When the gelatin is congealed, the plate is placed upon a 

 little glass bench or stand in the moist chamber. 



The Moist Chamber. Prepared out of two glass dishes, as 

 for the potato-cultures. The glass benches are so arranged that 

 one stands upon the other (Fig. 33). In order to avoid con- 

 fusion, a slip of paper with a number written on it is placed 



Fig- 33- Moist chamber with plates on benches. 



on the bench beneath each plate. As the original or first plate 

 would have the colonies developed in greatest profusion, it is 

 placed the first day on the topmost bench; but, since the colonies 

 would be likely to overrun the plate and allow the gelatin to 

 drop on the lower plates, it is best, as soon as evidences of growth 

 appear, to place it below, and watch the third plate or second 



Fig. 34. Petri dish for making plate cultures. 



dilution for the characteristic colonies, forgetting not all this 

 time to change the numbers accordingly. 



The date of culture and the name can be written upon the 

 moist chamber. 



Petri Saucers. Agar hardens very quickly, even without 

 any especial means for cooling, and it does not adhere very 

 well to the glass. Therefore it is better to follow the method 



