STERILIZATION BY HEAT. 73 



penetrating power of the steam is not only more ener- 

 getic, but the temperature at which sterilization is ordi- 

 narily accomplished is, as a rule, not destructive to the 

 objects under treatment. This is conspicuously seen in 

 the work of the laboratory; the culture-media, com- 

 posed in the main of decomposable organic materials 

 that would be rendered entirely worthless if exposed to 

 the dry method of sterilization, sustain no injury what- 

 ever when intelligently subjected to an equally effective 

 sterilization with steam. The same may be said of cot- 

 ton and woollen fabrics, bedding, clothing, etc. 



Aside from the relations of the two methods to the 

 materials to be sterilized, their action toward the or- 

 ganisms to be destroyed is quite different. The pene- 

 trating power of steam renders it by far the more effi- 

 cient 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 pur- 

 poses it is necessary to remember that the two methods 

 have the following applications : 



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

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

 ware, such as flasks, test-tubes, culture-dishes, pipettes, 

 plates, etc. 



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. 



DISCONTINUED STERILIZATION. The manner in 



