CULTURE MEDIA 67 



of bacteria include the selection of food media, the securing 

 and maintaining its sterility, and the methods of isolation 

 and subculturing. 



Character of Food required by Bacteria. The kind of 

 food required by bacteria varies greatly with the different 

 forms. Some require, for instance, living organic matter; 

 others require and live only on dead organic matter; while 

 still others live only in the absence of organic matter. 

 Attempts have been made to supply a universal medium. 

 This is evidently an impossibility. Media have been devised, 

 however, which furnish a good pabulum for a large number 

 of bacteria. Various decoctions have been used in the past, 

 such as those from fruit, wheat, pea straw, manure, etc. ; 

 but the medium most universally used at the present time 

 is that suggested by Loeffler, which is a beef broth or bouillon. 

 Upon this medium most of the bacteria can grow when ap- 

 propriate additions have been made, with the exception of those 

 bacteria which require living organic matter; that is, the obli- 

 gate parasites and the bacteria which live only on inorganic 

 food substances. 



Composition and Preparation of Various Culture Media. 

 A large number of different culture media have been devised 

 and are in constant use, but an attempt will be made here to 

 discuss only those that are most commonly used, and such 

 discussions will be only of a general nature. It will be 

 necessary to refer to laboratory guides for the exact for- 

 mulae and methods of preparation. Culture media may be 



