20 CULTURE MEDIA 



thoroughly wet with water before pouring on the bouillon. This is to 

 prevent clogging of the pores of the filter-paper. Make up the quantity 

 of filtrate to 1000 c.c. by adding water. 



If greater exactness is demanded than answers for ordinary clinical work, it is 

 advisable to again titrate and again adjust the reaction or to simply record the exact 

 reaction. It is more convenient to have a counterpoise to balance the inner compart- 

 ment and then to add water to the medium until a kilo weight, in addition to the 

 weight balancing the container, is just balanced. Then titrate, adjust the reaction 

 (if so desired), and filter. Sterilize in the autoclave at 115 C. for fifteen minutes 

 or in the Arnold on three successive days. The use of a balance is preferable in the 

 preparation of bouillon, necessary in making gelatin and imperative in making 

 agar media. 



BOUILLON MADE FROM LIEBIG'S MEAT EXTRACT. 



Place in a mortar 3 grams of Liebig's extract, 10 grams of peptone and 5 grams 

 of sodium chloride. Dissolve the whites of one or two eggs in 1000 c.c. of water. 

 Then add this egg-white water, little by little, to the extract, peptone, and 

 salt in the mortar until a brownish solution is obtained. Pour this into the inner 

 compartment of a rice cooker; apply heat to the outer compartment containing 

 the salt or calcium chloride solution, allow to come to a boil and to continue 

 boiling for fifteen to twenty minutes. Do not stir. Place inner compart ment 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 +0.75 

 (from +0.6 to +0.9). Consequently for growing bacteria it is unnecessary to titrate 

 and adjust reactions 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. 



