CHAPTER VII 



THE PREPARATION OF CULTURE MEDIA 



GENERAL TECHNIQUE 



The successful cultivation of bacteria upon artificial media requires 

 the establishment of an environment which shall be suitable in regard to 

 the presence of assimilable nutritive material, moisture, and osmotic 

 relations. These requirements are fulfilled in the composition of the 

 nutrient media described in another section, media which are to some 

 extent varied according to the special requirements of the bacteria 

 which are to be cultivated. If cultivation, furthermore, is to have any 

 value for scientific study of individual species, it is necessary to ob- 

 tain these species free from other varieties of microorganisms, that is, 

 in pure culture, and to protect such cultures continuously from con- 

 tamination with the other innumerable species which are everywhere 

 present. 



The technique which is employed for these purposes has been gradu- 

 ally evolved from the methods originally devised by Pasteur, Koch. 

 Cohn, and others. 



Bacterial cultivation is carried out in glassware of varied construc- 

 tion, the forms most commonly employed being test tubes of various 

 sizes, Erlenmeyer flasks, the common Florence flasks, and Petri dishes. 

 All glassware, of course, must be thoroughly cleansed before being used. 



Preparation of Glassware. — The cleansing of glassware may be ac- 

 complished by any one of a number of methods. New glassware may 

 be immersed in a one per cent solution of hydrochloric or nitric acid in 

 order to remove the free alkali which is occasionally present on such glass. 

 It is then transferred to a one per cent sodium hydrate solution for a 

 few hours, and following this is washed in hot running water. 



In the case of old glassware which has contained culture media, 

 sterilization in the autoclave is first carried out, then the glassware is 

 boiled in five per cent soda solution or in soapsuds. After this, thorough 

 mechanical cleansing is practiced, and the glassware may be treated by 

 acid and alkali followed by running water, as given above. These last 

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