STERILIZATION 43 



temperature for a long time, and this is achieved by the use 

 of an object slide surrounded by warm water. These organ- 

 isms are cultivated artificially only with great difficulty, 

 and the use of special stains is required for the purpose of 

 practical clinical diagnosis. 



STERILIZATION. 



For a better understanding of the technic of laboratory 

 procedure, the preparation of the foodstuffs or media on 

 which bacteria thrive will be briefly considered. They are 

 prepared from meat or its extracts, a substance called pep- 

 tone, and salt, and adjusted to a suitable reaction of weak 

 alkalinity, according to carefully worked-out formulae, which 

 are the result of long experimentation. They are stored or 

 distributed in glassware, which is of the non-corrosive type. 

 This glassware is cleaned with soap and water, sand or alcohol, 

 and rinsed with distilled water. It is then sterilized by hot 

 air. The glassware and media are sterilized because bacteria 

 are ubiquitous, and apparatus and foodstuffs wholly free from 

 microorganisms are necessary in bacteriological technic. In 

 no other way can one be sure of obtaining germs in pure 

 culture, that is, only one kind. After the medium has been 

 put into the glassware, steam sterilization is used; dry heat 

 is ineffectual and destroys the medium. The best method 

 of sterilization is by the autoclave or pressure boiler, since 

 all organisms are killed by one atmosphere of pressure to the 

 square inch in addition to the ordinary atmospheric pressure. 

 Because of the delicacy of some of the nutrient media it is, 

 however, necessary to sterilize these at the usual pressure of 

 the atmosphere in streaming steam. For this purpose a 

 double- jacketed boiler with the steam introduced into the 

 inner chamber (Arnold steam sterilizer) is used. 



While this sufficiently indicates the use of sterilization for 

 the preparation of food for bacteria, a few words upon sterili- 



