INOCULATION OF CULTURE-MEDIA 



81 



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 bacil- 

 lus 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 cul- 

 ture, 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. 



Fermentation Tube. For show- 

 ing the presence of gas or fermenta- 

 tion the Smith tube (Fig. 25) or some 

 of its modifications must be used. 

 The closed end and part of the bulb 

 are filled with the glucose or dextrose 



bouillon and sterilized at low temperatures for three succes- 

 sive days, then inoculated and placed in the incubator. Gas 

 forms gradually, displacing the fluid in the closed end. 



Fig. 25. Smith's fer- 

 mentation tube. 



