22 CULTURE MEDIA. 



cooker, bringing to a boil without stirring, allowing to boil fifteen 

 minutes and then filtering through absorbent cotton in a hot funnel, 

 we obtain a satisfactory medium, the reaction of which will be from 

 + .7 to +.9. 



GLUCOSE AGAR. 



Add the agar to i or 2% glucose bouillon and proceed as for ordinary 

 agar. 



GLYCERIN AGAR. 

 Add the agar to 6% glycerin bouillon instead of nutrient bouillon. 



GLYCERIN AGAR EGG MEDIUM. 



Take the white and the yolk of one egg and mix thoroughly in a 

 vessel kept between 45 and 55 C. with an equal amount of glycerin 

 agar. Tube the medium, inspissate in a rice cooker as for serum 

 tubes, and sterilize as for blood-serum tubes. 



This makes an excellent medium for growing tubercle bacilli. As 

 egg medium has a tendency to be dry, it is well to add i c.c. of glycerin 

 bouillon to each slant before autoclaving. 



NUTRIENT GELATIN. 



Add about 12% (120 grams) of "gold label" gelatin to 1000 c.c. 

 of nutrient bouillon in a rice cooker. If the bouillon had a reaction of 

 about +i, the gelatin solution will be about +3.5, so that it is always 

 necessary to titrate gelatin and neutralize to about +i. The pro- 

 cedure is the same as for bouillon. As the color reaction is not quite 

 as distinct with gelatin, it is better to make a color standard with 4 

 or 5 c.c. of the gelatin medium in 50 c.c. of water, instead of using 

 the distilled water alone, as was recommended for bouillon. 



Having neutralized and allowed to boil for fifteen minutes, we filter 

 through filter-paper in a hot funnel. As it is very important that 

 gelatin should be perfectly clear, it is better to filter through filter- 

 paper than through cotton. The filter paper should be very thoroughly 

 wetted with very hot water before filtering gelatine or agar. 



Tube the medium and sterilize, either in the Arnold on three 



