STERILIZATION AND DISINFECTION 67 



oratory largely for sterilizing culture media. It is some- 

 times used for sterilizing surgical dressings and certain 

 glassware that might be injured by the high temperature in 

 dry air. 



(c) Dry steam or steam under pressure. This is ob- 

 tained in the autoclave or steam chest. A pressure of from 

 10 to 20 pounds or more is employed. It is used frequently 

 in making and sterilizing certain culture media. There are, 

 however, certain objections to the use of such a high tem- 

 perature in the preparation of most media, especially those 

 in which bouillon forms the essential nutritive portion. Ster- 

 ilizers of this kind are used for sterilizing certain apparatus, 

 instruments and surgical dressings. They, are largely em- 

 ployed, however, for sterilizing or disinfecting clothing and 

 bedding after known infection. It is necessary to have the 

 steam under pressure in order to give it sufficient penetra- 

 ting power. 



3. Chemicals. Certain chemicals which possess high 

 germicidal action may be used for disinfecting certain arti- 

 cles such as harnesses, halters and instruments. Chemicals 

 are also employed to sterilize or disinfect the field of opera- 

 tion. Ordinarily when chemicals are employed the process 

 is called disinfection. In using chemicals to sterilize any 

 substance the effect of the chemical upon said substance 

 should be known. Solutions of the chemical sufficiently 

 strong to kill the organisms must be used. 



4. Filters. Filters are sometimes used to remove all 

 bacteria from certain fluids used in the laboratory. This 

 method is sometimes employed for sterilizing water. In 

 order to sterilize a liquid by means of a filter it is necessary 

 to have a filter through which bacteria will not pass, to have 

 this filter sterilized, and the filtrate must pass directly into 

 a sterilized flask or other receptacle. The filters that can be 

 used for this purpose are the Chamberland (Pasteur), Kit- 

 asato, and the Berkefeld bougies. There are different grades 

 of these but none of them can be continuously used for a 

 very long time without resterilization as the bacteria will 



