20 CULTURE MEDIA. 



boiling for fifteen to twenty minutes. Do not stir. Place inner com- 

 partment on the scales and its counterpoise and a one-kilo weight on 

 the other side. Add water until the two arms balance. Filter and 

 sterilize. 



The reaction of media made with Liebig's meat extract rarely 

 exceeds +.75 (from +.6 to +.9). Consequently for growing bacteria 

 it is unnecessary to titrate and adjust reaction unless precision is 

 demanded. 



SUGAR-FREE BOUILLON. 



Inoculate' nutrient bouillon in a flask with the colon bacillus. 

 Allow to incubate at 37 C. over night. Pour the contents into a sauce- 

 pan and bring to a boil to kill the colon bacilli. Put about 15 grams 

 of purified talc (Talcum purificatum, U. S. P.) in a mortar. Add the 

 dead colon culture, stirring constantly. Then filter through filter- 

 paper. It may be necessary to again pass the filtrate through the 

 same filter until the sugar-free bouillon is perfectly clear. 



For all ordinary purposes the very small amount of sugar in bouillon 

 made from Liebig's meat extract may be neglected in determining gas 

 production; so that under such conditions the various sugars could be 

 added directly to the meat-extract bouillon. 



SUGAR BOUILLONS. 



The sugar media ordinarily used for determining fermentation 

 or gas production are those of glucose and lactose. In special work 

 such carbohydrates as saccharose and maltose are used. The alcohol 

 mannite is used in differentiating strains of dysentery bacilli. 



To make, simply dissolve i or 2% of the sugar in sugar-free bouillon 

 or that made from meat extract. Tube in Durham's or the ordinary 

 fermentation tubes and sterilize in the autoclave at only about 5 

 pounds' pressure for 15 minutes, or in the Arnold. 



GLYCERIN BOUILLON. 



Add 6% of glycerin to ordinary bouillon. It is chiefly used in the 

 cultivation of tubercle bacilli. 



