INGREDIENTS OF CULTURE MEDIA 291 



Bacto-Gelatin is a high grade gelatin in granular form for convenience in 

 handling. This granular form of gelatin is readily soluble in warm water. Solu- 

 tions of Bacto-Gelatin are light in color and sparklingly clear in appearance. 

 They generally require no adjustment of reaction when used in culture media, as 

 in the Nutrient Gelatin described in "Standard Methods of Water Analysis" of 

 the American Public Health Association. In a 12 per cent concentration Bacto- 

 Gelatin has a melting point between 28 and 30° C. and a reaction of pH 6.8. 



The use of Bacto-Gelatin in culture media for studies of gelatinolysis (elabo- 

 ration of gelatinolytic enzymes) by bacteria is recommended by the Committee 

 on Bacteriological Technic^ of the Society of American Bacteriologists. Levine 

 and Carpenter- and Levine and Shaw^ also employed Bacto-Gelatin in the media 

 used in their studies of gelatin liquefaction. Garner and Tillett* used culture 

 media prepared with Bacto-Gelatin in their study of the fibrinolytic activity of 

 hemolytic streptococci. 



The formula for Nutrient Gelatin as given in "Standard Methods" specifies 



the use of 12 per cent gelatin. Other formulae may call for larger or smaller 



quantities of gelatin or for combinations of gelatin and agar. 



1 Pure Culture Study of Bacteria, 4:No.3:i936. ^ J. Bact., 9:225:1924. 



3 J. Bact., 8:297:1923. * J. Exp. Med., 60:255:1934. 



CARBOHYDRATES, POLYHYDRIC 

 ALCOHOLS, AND GLUCOSIDES 



Carbohydrates, polyhydric alcohols, glucosides and salts of organic acids are 

 extensively employed in culture media as a source of energy for bacteria and, 

 more particularly, for differentiating genera and identifying species. The ability 

 of an organism to attack a particular carbohydrate is a definite characteristic of 

 bacterial species and under controlled conditions remains constant for the organ- 

 ism throughout generations of cultivation on media. 



These carbohydrates, polyhydric alcohols, glucosides and salts of organic acids 

 are prepared with the utmost care to eliminate admixtures, other sugars or con- 

 taminating materials. They are standardized to the highest known degree of 

 purity, having in view the consensus of authority concerning their respective 

 properties. In addition to the carbohydrates described below we also prepare 

 filter sterilized solutions of a selected number of carbohydrates. These solutions 

 are prepared in 10 per cent concentration and are discussed on page 293. 



B AGTO-DEXTROSE ( B 1 55 ) 



Bacto-Dextrose is a specially prepared dextrose (c?-glucose) of unusual purity, 

 recommended for use as a readily available source of energy for bacteria and 

 also for fermentation studies. It is free from all other sugars and from starch, 

 proteins, alcohol and heavy metals. In appearance it is a pure white crystalline 

 powder. Its specific rotation lies between -f 52.5 and -|-52.76. 



Bacto-Dextrose is widely used in studies of the fermentative processes of 

 bacteria. In fluid media it is usually employed in a concentration of 0.5 per cent, 

 but in solid media it may be used in higher concentrations. Dextrose media also 

 have a distinct value in the rejuvenation of cultures because this carbohydrate 

 is readily assimilated by most bacteria. As small an amount of dextrose as 0.05 



