INOCULATION OF GELATIN AND AGAR 67 



of Petri and use little shallow glass dishes, one covering the 

 other (Fig. 34) . They are first sterilized by dry heat, and then 

 the inoculated gelatin or agar is poured into 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, and does away 

 with the cooling apparatus and moist chamber; the saucers 

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

 have entirely superseded them. 



Esmarch's Tubes or Rolled Cultures. This method, 

 especially used in the culture of anaerobic germs, consists in 

 spreading the inoculated gelatin 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 

 gelatin around the cotton plug. 



The tubes can be placed directly under the microscope for 

 further examination of the colonies. 



Animals as Culture Media. It is almost impossible to 

 separate certain organisms, such as the tubercle bacillus and 

 pneumococcus, from mixed cultures by ordinary plate methods, 

 and the plan of producing the disease in animals by inoculation, 

 and then obtaining the organism in pure culture, has to be 

 employed. 



Pure Cultures by Boiling. Spored organisms may be 

 separated from others by boiling the mixture for a few 

 minutes, when all the non-spored forms will perish, and only 

 the spores remain to germinate subsequently. 



