Sterilization of Media 129 
Lactose agar.—To 1 liter of bouillon add 1.5 per 
cent of agar (15 grams). Allow the agar to soak for 
one-half hour. Record weight, then add 10 grams of 
lactose. Steam for 20 minutes, cool to 60° C.; titrate 
to +1 per cent acidity, add the white of an egg 
shaken up in 380 c.c. of water and steam for 20 to 30 
minutes; then boil until clear, taking eare not to 
burn it. Restore weight by adding water, then filter 
through cheese-cloth and absorbent cotton. The agar 
should be clear and of a yellowish straw color. Fill 
the test tubes, 10 c.c. to a tube, plug them with 
cotton and then sterilize them. 
Gelatin.—To one liter of bouillon add 12 per cent 
of a good grade of gelatin. Weigh the dish and 
material. Dissolve the gelatin and titrate to 1 per 
cent acidity, boil 15 minutes, cool, add the white of 
an egg shaken with 30 c.c. of water, boil again for 
15 minutes, restore weight, and filter through cheese- 
eloth and absorbent cotton. Place in test tubes, 10 
e.c. per tube, plug and sterilize. 
Lactose gelatin.—Prepare as for gelatin in previous 
paragraph, using 15 per cent gelatin and 1 per cent 
lactose (milk sugar). In filling the tubes, use exactly 
8 c.c., if litmus is to be added, otherwise 10 c.c. per 
tube; plug and sterilize as before. 
Litmus.—Soak 100 grams of litmus cubes in 600 
e.c. of water for 24 hours. Filter through filter 
paper and make up to original volume. Titrate the 
litmus solution so that the acidity will be the same 
as for media, viz.: +1 per cent. As it is too alka- 
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