68 PHARMACEUTICAL BACTERIOLOGY 



It is, of course, evident that in the above process of sterilization the 

 temperature does not exceed 100 C., and it maybe less in certain portions 

 of the sterilizer, steamer, or cooker, say, 95 to 97 C. Certain kinds of 

 sterilizations are done by steam under pressure. The apparatus used 

 for this purpose is known as autoclave. It consists of a strong steam 

 cylinder with a screwed-down top, safety valve, steam gauge, and ther- 

 mometer. The articles (media, etc.) to be sterilized are placed inside, 

 the top is securely fastened down, steam is generated until the thermometer 

 registers, say, 1 20 C . The temperature is kept up to that degree for about 

 10 to 20 minutes, which is sufficient to destroy all life, including spores. 

 For certain purposes the autoclave is not applicable. Blood serum, gelatin 

 media, and all media containing carbohydrates, undergo certain chemical 

 changes when the temperature is raised above 100 C., or even if kept at 

 100 C. for a long time or for a short time, if oft repeated. The autoclave 

 is convenient for sterilizing discarded cultures, test-tubes, and glassware 

 generally, and such media as beef broth and agar. 



In many instances it is desirable to sterilize at a temperature lower 

 than 100 C. Albumen and blood serum, for instance, will coagulate at 

 that temperature. Again, it is desired to kill the microbes without de- 

 stroying the toxins which they form, as in the manufacture of bacterial 

 vaccines. In the sterilization (pasteurization) of milk, a lower tempera- 

 ture is employed. In the sterilization of these and other substances the 

 temperature ranges from 50 to 85 C. The discontinuous method is 

 employed, differing from the method already described in that the period 

 of exposure is much prolonged, about one hour. The number of daily 

 exposures ranges from one to six. For example, milk exposed to a tem- 

 perature of 60 to 70 C. for one hour is considered sufficiently sterilized, 

 whereas blood serum is subjected to hourly exposures of a temperature 

 of 60 C. for six successive days before it is pronounced completely 

 sterilized. 



5. Preparation of Culture Media 



The pharmacist should give especial attention to the preparation of 

 bacterial culture media, as in this he may be of service to the physician. 

 The busy general practitioner who is not equipped with a suitable bacterio- 

 logical laboratory, or who does not have time to prepare culture media, 

 would no doubt consider it a very decided advantage should the pharma- 

 cist offer to assist him. This will be more fully set forth in the last 

 chapter. 



In brief, it may be stated that microbes feed upon the same substances 

 that we feed upon. In the presence of adequate warmth and moisture 

 they attack all organic substances. This being the case, it may readily 

 be assumed that there are many substances or media which can be used 



