CHAPTER III. 



CULTIVATION OF BACTERIA PREPARATION OF MEDIA. 



IN order that bacteria may be studied properly, it is neces- 

 sary that we have some means at our command by which we 

 can observe the growth and development of the individual 

 organism and note its cultural characteristics. For this pur- 

 pose they are grown on media having a standard composition 

 and one which is most suitable for observation. 



A great variety of different media has been proposed ; but 

 it is necessary to mention only those which are the most useful 

 and which may be used for general work in any laboratory. 

 In the preparation of a medium, the aim must be to approxi- 

 mate the body-juices as nearly as possible. The best media are 

 those which can easily be liquefied and solidified, since these 

 permit of the most accurate observation. All media must 

 contain at least 80 per cent, of water. The reaction should 

 be neutral or slightly alkaline. Some bacteria require a 

 special culture-medium ; and this will be described later 

 when such organisms are considered. 



Bouillon or Beef-tea : This is the most easily prepared and 

 the most useful of all the media used in the laboratory. It 

 also forms the basis of nutrient gelatin and agar-agar. It 

 can be prepared from chopped beef or from the extract, which 

 is more convenient and answers all practical purposes : 



Beef-extract (Liebig), 2 grams ; 



Dried peptone (powdered) (Witte), 10 " 

 Sodium chloride (table salt), 5 " 



Distilled water, 1000 c.c. 



Mix the beef-extract with a little water until it is thor- 

 oughly dissolved. Add the peptone gradually, avoiding 



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