68 METHODS USED IN THE STUDY OF BACTERIA 



roughly divided into those containing albuminous matter, and 

 these may be either liquid, solid, or liquefiable solid media, 

 and nonalbuminous or synthetic media. 



Albuminous or Protein Media 



Liquid Media 



Bouillon. This medium is the basis of most of the ordinary 

 media used in the laboratory, such as gelatin and agar, and is 

 also largely used as a culture medium itself. It has the fol- 

 lowing ingredients. The extractions of 500 grams of lean 

 beef, 10 grams of peptone, 5 grams of sodium chloride, neu- 

 tralized and dissolved in one liter of distilled water. The nutri- 

 tive value of the various ingredients is a subject that should be 

 briefly considered at this point. The nutritive value of the 

 meat depends almost entirely upon the albuminous sub- 

 stances of which it is composed, but most of these are insoluble 

 and most of them that do go into solution are precipitated on 

 heating, so that very little protein material is furnished by 

 the meat. Its purpose in the medium is largely to furnish ex- 

 tractives, chiefly creatin and xanthin bodies, which are useful 

 to most bacteria. The peptone, which is a soluble albumin, 

 formed from proteins by the action of the gastric juice, is 

 the principal source of nitrogen for the bacteria. The so- 

 dium chloride was originally used to aid in the solution of 

 the peptone, but it is now not needed for that purpose and in 

 some laboratories its use is being discarded. 



