36 METHODS OF CULTIVATION OF BACTERIA. 



The temperature necessary varies with different bacteria, 

 and the vehicle of heat is also of great importance. The 

 two vehicles employed are hot air and hot water or steam. 

 The former is usually referred to as " dry heat," the latter 

 as " moist heat." As showing the different effects of the 

 two vehicles, Koch found, for instance, that the spores of 

 bacillus anthracis, which were killed by moist heat at 100 C., 

 in one hour, required three hours' dry heat at 140 C. to 

 effect death. Both forms of heat may be applied at 

 different temperatures in the case of moist heat above 

 100 C., a pressure higher than that of the atmosphere must 

 of course be present. 



A. Sterilisation by Dry Heat. 



(i) Red Heat or Dull Red Heat. Red heat is used for 

 the sterilisation of the platinum needles which, it will be 



found, are so constantly in 

 use. A dull heat is used 

 for cauteries, the points of 

 forceps, and may be used 

 for the incidental sterilisation 

 of small glass objects (cover- 

 slips, slides, occasionally 

 when necessary even test- 

 tubes), care of course being 

 taken not to melt the glass. 

 The heat is obtained by an 

 ordinary Bunsen burner. 



(2) Sterilisation by Dry 

 Heat in a Hot-Air Chamber. 

 The chamber (Fig. 2) con- 

 sists of an outer and inner 

 case of sheet iron. In the 

 bottom of the outer there is 

 a large hole. A Bunsen is lit beneath this, and thus plays on 

 the bottom of the inner case, round all of the sides of which 

 the hot air rises and escapes through holes in the top of the 



FIG. 2. Hot-air steriliser. 



