28 CULTURE MEDIA 



NUTRIENT GELATIN 



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 meat extract, peptone and salt, 

 in the mortar, until a brownish solution is obtained. Pour this into the inner com- 

 partment of the rice cooker and bring the temperature up to 45C. (This prelim- 

 inary elevation of temperature is better carried out in some heated water in a pan, 

 as the heating by means of the salt solution in the outer compartment of the rice 

 cooker is difficult to control, so that a temperature approximating 7oC. might be 

 obtained and the albumin of the white of egg coagulated. The temperature in 

 the outer compartment might be approaching boiling before the contents of the inner 

 compartment would show 45C.) Now take about 120 grams of "gold label" or 

 other good quality gelatin (12%) and crush it down in the meat extract egg- water 

 solution in the inner compartment of the rice cooker. 



The gelatin quickly goes into solution at 45C. Gelatin being quite acid it will 

 probably be found upon titration that the reaction is about +4%. ' N/i NaOH 

 solution is added to bring the reaction to about +1% or 3 c.c. of N/i NaOH for 

 each 100 c.c., provided the reaction were exactly +4%- The procedure is the same 

 as for bouillon. The color reaction is not quite as distinct with gelatin as with 

 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 gelatin or agar. 



Tube the medium and sterilize, either in the Arnold on three successive days or in 

 the autoclave at 8-10 pounds' pressure for ten minutes. The tubes should be 

 cooled as quickly as possible in cold water after taking out of the sterilizer. 



AGAR GELATIN MEDIUM (NORTH) 



Lean chopped beef or veal 500 grams. 



Agar 10 grams. 



Gelatin, Gold label 20 grams. 



Peptone, Witte's, 20 grams. 



Sodium chloride 5 grams. 



Distilled water, q.s . 1000 c.c. 



Extract the chopped beef with 500 c.c. distilled water for eighteen hours, strain 

 through muslin and combine the ingredients in the usual way. Adjust the reaction 

 to the neutral point, using phenolphthalein as indicator. 



North states that this medium is excellent for streptococci, pneumococci and 

 diphtheria bacilli because it is soft, moist, and can be used at 37C. 



It is claimed to be of special value for carrying stock cultures. It is useful as a 

 plating medium for milk. 



LITMUS MILK 



Milk for media should be as fresh as possible. It should then be put in a 1000- 

 c.c. Erlenmeyer flask, sterilized for fifteen minutes in the Arnold, and set over night 



