CULTURE MEDIA. 55 



Gelatine. To 1,000 cc. of the stock broth add 120 

 grammes of gelatine (" gold label ") cut up into small 

 pieces. Dissolve carefully over a water bath, and neut- 

 ralize if necessary with sodium carbonate. Place in a 

 flask, cool down to 60°C and add the whites of two eggs. 

 Steam for ^ hour in the sterilizer and filter through 

 moistened filter sheets, using a warming funnel. 

 Steam in the sterilizer for 20 minutes on 3 successive 

 days. Tubes are treated in same manner as broth 

 tubes. 



Grape Sugar Gelatine is stock gelatine to which 1 

 to 2% of grape sugar has been added. 



Agar-Agar. Cut up 15 grammes of agar-agar fibre 

 fine, and allow to' soak in .5% acetic acid for 2 

 hours. Then wash repeatedly in water to free from 

 all traces of the acid. Place in a flask with 1,000 

 cc. of stock broth, and dissolve by heating in the auto- 

 clave, up to 120°C. After removal from the autoclave, 

 neutralize if necessary with sodium carbonate, cool to 

 60°C, and add the whites of two eggs dissolved in 50 cc. 

 of water. Cook in the autoclave for 10 minutes at 

 110°O, and filter through moistened filter sheets, using 

 a warming funnel. As a rule the agar runs through 

 rapidly. If it tends to clog, immediately replace by 

 fresh paper, keeping the unfiltered solution hot. Steri- 

 lize the filtered agar in the autoclave for 20 minutes at 

 120^'C. 



Another method which is very satisfactory is that of 

 Ravenel, viz., 



