CHARACTERS OF A BACTERIUM 



(Fig. 23); put in the small tubes open end downwards; plug 



with cotton wool and sterilize for half an hour 



on three successive days : the small inner tube 



in each becomes completely filled with the 



broth. 



Now inoculate the medium with small portions 

 of the different colonies to be tested and incubate 

 at 37 C. If fermentation occurs the small 

 tube becomes partially filled with gas. 

 (b) With, Saccharimeter Tubes. 

 The closed end of the tube should be filled 

 completely and half the bulb also with glucose 

 beef broth (Fig. 24, a). After sterilization, 

 inoculate and incubate at 37 C. 



If gas is produced some of it will collect 

 near the closed end of the tube (Fig. 24, b). 



It is useful to have the limb of some of the 

 tubes graduated. Note the amount collected 



after two or 

 three days ; 

 then add i 

 or 2 c.c. of 



strong caustic TZSsKS? 

 potash solution. 



Some of the gas is ab- 

 sorbed, the diminution re- 

 presenting the amount of 

 carbon dioxide present ; what 

 is left is in most cases 

 hydrogen, so that the ratio 

 of CO 2 to H can be calcu- 

 lated. 



If the medium is cloudy 



FIG. 24. Saccharimeter tubes. 

 a Full; b after inoculation and production of gas. 



only in the bulb, the organism is aerobic ; where the upper 

 end of the tube is cloudy and the medium below remains 



