22 CULTURE MEDIA 



alkaline, so that if i 1/2 to 2% of agar is added to nutrient bouillon having a reaction 

 of +i the finished product will be found to be about +0.8. 



To make: Weight out 15 to 20 grams of powdered agar and place in a mortar. 

 Make a paste by adding nutrient bouillon, little by little, and when a smooth even 

 mixture is made, pour in into the inner compartment of a rice cooker and add the 

 remainder of the 1000 c.c of bouillon. The use of the balance is preferable. 



The outer compartment of the rice cooker should contain the 25% salt solution. 

 Bring to boil, and the agar will be found to have entirely gone into solution after 

 five to ten minutes of boiling. 



Then, using a funnel which has been heated in boiling water and which contains 

 a small pledget of absorbent cotton, we filter the agar, tube it, and sterilize it in the 

 autoclave or Arnold. One and one-half percent agar can be readily filtered through 

 filter-paper and gives a clearer medium. 



By taking of meat extract 3 grams, peptone 10 grams, salt 5 grams, powdered 

 agar 15 grams, the white of one egg and 1000 c.c. of water, making at first apasteof 

 all the ingredients in a mortar, then gradually adding the remainder of the 1000 c.c. 

 of water, putting in the rice cooker, bringing to a boil without stirring, allowing to 

 boil fifteen minutes and then filtering through absorbent cotton placed between two 

 layers of gauze in a hot funnel, we obtain a satisfactory medium, the reaction of 

 which will be from -fo. 7 to +0.9. It is very important not to interfere with the pul- 

 taceous coagulum which forms on the surface of the boiling agar. 



Where very exact adjustment of the reaction of the finished pro- 

 duct is desirable the method of preparation of the Committee on 

 Water Analysis of the American Public Health Association is to be 

 preferred. 



Dissolve 15 grams of agar in 500 c.c. of water in the inner compartment of the 

 rice cooker previously described. After the agar is in solution (after 10 to 15 minutes 

 boiling) remove the inner compartment, containing the 3% agar solution, and 

 allow it to cool to about 55 C. Mix in the mortar, as described in the 

 directions for making nutrient bouillon from Liebig's extract, 3 grams of Liebig's 

 extract, 10 grams of peptone and 5 grams of sodium chloride in 500 c.c. of water 

 containing the whites of one or two eggs. Heat this mixture to 50 to 55 C. and pour 

 it into the agar solution, in the inner compartment, which has been cooled to about 

 55 C. Now titrate this mixture containing 500 c.c. of double strength agar and 500 

 c.c. of double strength peptone, meat extract and salt solution. The resulting 

 1000 c.c. gives i 1/2% agar and i% peptone solution. Having adjusted the 

 reaction by the addition of the necessary amount of N/i acid or alkali, we place the 

 inner compartment in the outer one of the rice cooker, bring to a boil and filter 

 through filter-paper which has been wetted with boiling water. The filtration can 

 be carried out in the autoclave or in an Arnold sterilizer. Of course the ordinary 

 filtering through gauze and cotton will answer where clearer media is not an object. 



GLUCOSE AGAR. 



Add the agar to i or 2% glucose bouillon and proceed as for ordinary agar. If 

 preferred, the glucose agar can be made by rubbing up meat extract 3 grams, peptone 



