PREPARATION OF CULTURE MEDIA 



29 



Rubber Stoppers and Tubing should never be heated, they 

 should be cleansed with soap and water and allowed to stand for 

 one hour in a 1 to 1000 solution of bichlorid of mercury, then 

 washed with sterile water before using. 



CULTURE MEDIA 



One of the points to be observed in the artificial culture of bac- 

 teria is that the food medium supplied should resemble as closely as 

 possible that to which the 

 organism is accustomed. 

 Many species grow luxu- 

 riantly if only a simple 

 nitrogen and carbon com- 

 pound and some salt and 

 water are present; others 

 require more complex 

 substances. For certain 

 pathogenic bacteria body 

 fluids such as blood serum 

 and ascitic fluid are used. 

 The fact that certain spe- 

 cies will grow abundantly 

 on one kind of medium and not at all on another, or that char- 

 acteristic growth will occur on certain media, is often an aid in 

 the identification of species. 



The most commonly used media have as their basis a watery 

 extract of meat to which a small amount of peptone is added. 

 Koch found that by the addition of gelatin to this broth a solid 

 transparent medium would result on which growth from a single 

 organism could be obtained and on which also certain bacterial 

 characteristics became evident. Gelatin, however, has only a 

 limited use; it does not remain solid at the temperature best 

 suited for pathogenic microorganisms ; moreover, there are certain 

 species of bacteria which during their growth are able to liquefy 

 it at lower temperatures. To obviate these conditions agar, 



FIG. 8. Inspissator. 



