CHAPTER XV. 



Various experiments in sterilization by steam and by hot air. 



PLACE in one of the openings in the cover of the steam 

 sterilizer au accurate thermometer ; when the steam has 

 been streaming for a minute or two the thermometer will 

 register 100 C. ; wrap in a bundle of towels or rags or 

 pack tightly in cotton a maximum thermometer ; let this 

 thermometer be in the centre of a bundle large enough 

 to quite fill the chamber of the sterilizer. At the end 

 of a few minutes' exposure to the streaming steam re- 

 move it ; it will be found to indicate a temperature of 

 100 C. 



Closer study of the penetration of steam has taught 

 us, however, that the temperature which is found at the 

 centre of such a mass may sometimes be that of the air 

 in the meshes of the material, and not that of steam, 

 and for this reason the sterilization at that point may 

 not be complete, because hot air at 100 C. has not the 

 sterilizing properties that steam at the same temperature 

 possesses. It is necessary, therefore, that this air should 

 be expelled from the meshes of the material and its place 

 taken by the steam before sterilization is complete. This 

 is insured by allowing the steam to stream through the 

 substances a few minutes before beginning to calculate 

 the time of exposure. There is as yet no absolutely 

 sure means of saying that the temperature at the centre 

 of the mass is that of hot air or of steam, so that the 



11 



