1 66 CULTURE MEDIA 



5. Keep the water in the steam can vigourously boil- 

 ing, and so steam at 100 C., bubbling through the 

 medium mass, for ten minutes, by which time complete 

 solution of the gelatine is effected. A certain amount 

 of steam will condense as water in the medium flask 

 during this process hence the necessity for the use 

 of double strength me.at extract but if the water 

 bath is kept boiling this condensation will not exceed 

 100 c.c. 



6. Weigh the flask and its contents; then (in 5* 

 grammes + weight of the flask) minus (weight of the 

 flask and its contents) equals the weight of water re- 

 quired to make up the bulk to i litre. The addition of 

 the requisite quantity of water is carried out as follows : 



In one pan of the trip balance place the counterpoise 

 of the tared flask (or its equivalent in weights) to- 

 gether with the weights making up the calculated 

 medium weight. In the opposite pan place the flask 

 containing the medium mass. Now add boiling 

 distilled water from a wash bottle until the two pans 

 are exactly balanced. 



7. Titrate and estimate the reaction of the medium 

 mass; control the result. Calculate the amount of 

 soda solution required to make the reaction of the 

 medium mass +10 (i. e., calculate for 1000 c.c., less 

 the quantity used for the titrations) . 



8. Add the necessary amount of soda solution and 

 heat in the steamer at 100 C. for twenty minutes, to 

 precipitate the phosphates, etc. 



9. Allow the medium mass to cool to 60 C. Well 

 whip the whites of two eggs, add to the contents of the 

 flask and replace in the steamer at 100 C. for about 

 half an hour (until the egg-albumen has coagulated 



1 This figure is obtained by adding together i litre water, 1000 grammes; 

 10 per cent, gelatine, 100 grammes; i per cent, peptone, 10 grammes; 0.5 

 per cent, salt, 5 grammes; total, 1115 grammes. Modifications of the above 

 process, as to quantities and percentages, will require corresponding altera- 

 tions of the figures. The average weight of a measured litre of 10 per cent, 

 nutrient gelatine when prepared in this way after filter at ion is 1080 grammes. 



