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 anthrads, 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. 



A. (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 for- 

 ceps, 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. 



A. (2) Sterilisation by 

 Dry Heat in a Hot -Air 

 Chamber. The chamber 

 (Fig. 2) consists 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 



FIG. 2. Hot-air steriliser. 



