CHAPTER III 



STERILIZATION OF GLASSWARE. PREPARATION OF 

 CULTURE MEDIA 



IN order to become familiar with the characteristics of any given 

 species of bacteria, it is necessary, first of all, to isolate it from every 

 other form. In nature it is seldom that one species is found grow- 

 ing alone. This does occur in certain diseases, but generally 

 speaking bacteria have to be taken from their natural surroundings 

 and grown on artificial food medium in order to be studied. 



The first essential then for bacterial study is to provide condi- 

 tions whereby one species may grow, without an admixture of 

 other forms. Since bacteria are practically everywhere this can 

 only be accomplished by first destroying all germs in the food 

 medium on which the organism is to be cultivated and on all appa- 

 ratus likely to come in contact with it. In order to do this one form 

 or another of sterilization is employed, the method used depending 

 largely upon the object to be sterilized ; the underlying principle 

 of each, however, is the destruction of bacteria by heat. Hot air 

 or " dry heat " is generally used for glassware and hot water or 

 steam, " moist heat," for culture media. 



Cleaning of Glassware. Before sterilization each article of 

 glassware should be perfectly clean. New glass as a rule only 

 requires washing with soap and water and the adherent dirt re- 

 moved with a test-tube brush. Old glassware containing cul- 

 tures should be sterilized either in the autoclave or boiled in 5 

 per cent solution of washing soda or soapsuds for one hour in a 

 covered boiler. Glassware may be further cleansed if necessary 

 by placing for one hour or more in the following chromic acid 

 mixture : 



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