CULTURAL REQUIREMENTS OF BACTERIA 315 



failed to give growth, although prepared with all due attention 

 to hj'drogen ion concentration, etc. The addition of as little 

 as 0.025 per cent glucose to such media at once improved them to 

 such a degree that marked growth occurred, and with twice 

 this rjuantity, growth was approximately as heavy as in the 

 average broth prepared without glucose. While the point has 

 not been verified experimentally, it is not improbable that most 

 meat contains small quantities of glucose or other carbohydrate, 

 and that occasionally this may be much diminished or absent. 

 For routine purposes, therefore, and in all experimental media, 

 0.1 per cent glucose is added. This quantity is insufficient to 

 produce acid in amounts great enough to kill the cultures in 

 twenty-four hours, or to interfere w^ith agglutination with 

 specific sera. 



Inorganic constituents 



Little is known definitely of the salt requirements of bacteria. 

 There is some e\'idence in the literature to indicate that they 

 are moderately elastic, and in any case such minute traces as may 

 be required, must occur in the peptone and meat infusion used 

 as routine media. Where these or similar substances are omitted, 

 small quantities of inorganic salts may well be required. The 

 nature of these can only be detennined when purified organic 

 compounds can replace the meat infusion and peptone. 



To guard as far as possible against failure of expeiimental 

 media to support growth through lack of inorganic material, 

 the same salt mixture which is used in Uschinsky's and other 

 similar media has been employed instead of simple NaCl, in 

 the preparation of all experimental media in which the ordinary 

 meat infusion is not used. 



To simplify the preparation of media, the salts are aU dissolved 

 in twice the concentration required, together with glucose, and 

 phenol red is added to this solution. ^ledia are prepared by 

 adding an equal volume of meat infusion or other solution to 

 this preparation, thereby reducing the concentrations of the 

 constituents to that desired. The composition of the solution 

 is shown below, and it wall be referred to subsequently as 

 "glucose-salt solution." 



