INOCULATION OF GELATINE AND AGAR. 



63 



evenly. If the plate is at all cool, the fluid will solidify as it is 

 being spread. The glass cover is replaced until the gelatine or 

 agar is quite solid to prevent contamination. 



FIG. 33. 



Moist chamber with plates on benches. 



When the gelatine 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. In order to avoid confusion, a slip 

 of paper with a number written on it is placed on the bench be- 

 neath 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 gelatine 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 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. There- 

 fore it is better to follow the method of 

 Petri and use little shallow glass dishes, 

 one covering the other. They are first 

 sterilized by dry heat, and then the in- 

 oculated gelatine or agar is poured into Petri 

 the lower dish, covered by the larger one, 



and placed in some cool place, different saucers being used for 

 each dilution. 



FIG. 34. 



