UNIVERSITY 



OF 



STERILIZATION BY HEAT. 51 



culture media, composed in the main of decomposable 

 organic materials that would be rendered entirely worth- 

 less if exposed to the dry method of sterilization, sustain 

 no injury whatever when intelligently subjected to an 

 equally effective sterilization with steam. The same 

 may be said of cotton and woollen fabrics, bedding, 

 clothing, etc. 



Aside from the relations of the two methods to the 

 materials to be sterilized, their action toward the organ- 

 isms to be destroyed is quite different. The penetrating 

 action of the steam renders it by far the more efficient 

 agent of the two. The spores of several organisms 

 which are killed by an exposure of but a few moments 

 to the action of steam, resist the destructive action of 

 dry heat at a higher temperature for a much greater 

 length of time. 



These differences will be strikingly brought out in the 

 experimental work on this subject. For our purposes 

 it is necessary to remember that the two methods have 

 the following applications : 



The dry method, at a temperature of 150-180 0., 

 for one hour, is employed for the sterilization of glass- 

 ware : flasks, test-tubes, culture dishes, pipettes, plates, 

 etc. 



The sterilization by steam is practised with all culture 

 media, whether fluid or solid. Bouillon, milk, gelatin, 

 agar-agar, potato, etc., are under no circumstances to be 

 subjected to dry heat. 



The way in which heat is employed in processes of 

 sterilization varies with circumstances. In its employ- 

 ment as dry heat its application is always continuous 

 i. e., the objects to be sterilized are simply exposed to 

 the proper temperature for the length of time necessary 



