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 an accurate thermometer; when the 

 steam has been streaming for a minute or two the ther- 

 mometer 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 remove it; it will be found to indi- 

 cate 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 

 exact length of time that is required for the expulsion 



