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 30 c. c. of water and steam for 20 to 30 

 minutes; then boil until clear, taking care 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- 

 cloth and absorbent cotton. Place in test tubes, 10 

 c. 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 

 c. 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- 



