CHAPTER III. 

 CULTURE MEDIA. 



Culture media are substances in which microbes are artificially 

 cultivated. The variety of such substances is very large, different 

 materials being suited to different purposes. Particular kinds 

 of media have been devised in order to bring to development or 

 especially to favor the development of certain kinds of microbes. 

 Various media are also used to demonstrate the physiological 

 properties of bacteria, especially the physical arrangement of the 

 bacterial cells as they grow under various conditions, and the 

 chemical changes induced in the various constituents of the 

 media by the microbic growth. 



Glassware. Micro-organisms are usually grown in glass 

 test-tubes or sometimes in glass flasks. The tubes and flasks 

 should be of more durable glass than those ordinarily used in 

 chemical work, but heavy tubes of glass of poor quality are not 

 to be recommended. For ordinary purposes, test-tubes I25X 

 15 mm. are convenient. Larger tubes, 150X20 mm., are used 

 to store media to be used in making plate cultures and for roll- 

 tube cultures. New glassware should be thoroughly washed 

 before using, and for critical work it should be boiled in dilute 

 sodium carbonate, rinsed, washed in dilute hydrochloric acid, 

 rinsed repeatedly in running water, finally in distilled water, 

 and then inverted to drain in a warm place, such as the incubator, 

 until perfectly dry. Used glassware should be sterilized in the 

 autoclave at 120 C. for half an hour, emptied, cleaned with a 

 swab and hot water, rinsed in distilled water and drained. In 

 case of special difficulty the glassware may, after emptying and 

 washing in water, be cleaned by soaking in a special cleaning fluid, 

 and all organic matter may be readily removed by using this 



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