ii] PREPARATION OF CULTURE MATERIAL 37 



In order to avoid the brown colour, which the nutritive 

 gelatine assumes when the grape sugar is added, and after 

 heating it, it is necessary to prepare a watery solution of the 

 required amount of grape sugar separately, to add this to 

 the solution of gelatine, peptone, and salt in beef broth, 

 then to make the whole alkaline and steam. The grape 

 sugar Agar differs from nutrient Agar described sub 6, in 

 containing 2 per cent, of grape sugar added in substance to 

 the Agar mixture before putting into the autoclave. 



8. Glycerin Agar, first used by Roux and Nocard for 

 the cultivation of the tubercle bacillus. It is, however, not 

 only useful for this, but also for other microbes. It is the 

 nutrient Agar mixture, sub 6, to which 5 to 8 per cent, 

 pure glycerin has been added before putting the mixture 

 into the autoclave. 



