INOCULATION OF GELATINE AND AGAR. 59 



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 



"Rrn *^Q 



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 saucers 

 the lower dish, covered by the larger one, 



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

 each dilution. 



This method is very useful for transportation ; the saucers can 

 be viewed under microscope similar to the glass plates, and has 

 in a manner superseded them. 



Esmarch's Tubes, or Rolled Cultures. This method, especially 

 used in the culture of anaerobic germs, consists in spreading the 

 inoculated gelatine upon the inner walls of the test tube in 

 which it is contained and allowing it to congeal. The colonies 

 then develop upon the sides of the tube without the aid of 

 other apparatus. The method is useful whenever a very quick 

 and easy way is required. The rolling of the tube is done under 

 ice-water or running water from the faucet. The tube is held 

 a little slanting, so as to avoid getting too much gelatine around 

 the cotton plug. 



The tubes can be placed directly under the microscope for 

 further examination of the colonies. 



NOTE. The peptone nutrient gelatine, blood serum and agar 

 can now be purchased already prepared, thus saving a great 

 deal of time and making unnecessary the purchase of consider- 

 able apparatus. 



