410 



CULTURE MEDIA FOR CULTIVATION OF MICROORGANISMS 



Preparation : 



(1) Dissolve 30.0 to 40.0 g. of agar in 

 200 to 400.0 cc. of water. 



(2) Add slowly, 700-800 cc. of alcohol 

 that has been acidified with 

 CH3COOH. 



(3) Shake the mixture thoroly and allow 

 the precipitated agar to settle. 



(4) Pour off the alcohol and place the agar 

 precipitate on a Biicher funnel. 



(5) Wash the precipitate until the wash 

 water is neutral. 



(6) The agar may be washed on a piece of 

 strain cloth instead of a Biicher 

 funnel. 



(7) After the alcohol has been removed 

 from the agar, the agar is dried at 

 100°C. 



(8) The dried agar is a snow white 

 powder. 



Use: A purified form of agar. When this 

 powdered agar is used in the preparation 

 of various media, it requires no filtration. 



Reference: Dominikiewicz (1908 p. 668). 



1400. Cunningham's Purified Agar 



Constituents : 



1. Water. 



2. China grass. 

 Preparation : 



(1) Weigh a quantity of china grass 

 and place in a vessel containing suffi- 

 cient dilute acid (0.01% H2SO4 gives 

 the best results) to completely cover 

 the fibre. 



(2) Soak in the acid for 10 minutes. 



(3) Remove and wash in running water 

 until all traces of acid have been 

 removed. Both the fibre and wash- 

 ings are to be alkaline to litmus. 



(4) Express the superfluous water by 

 placing the fibre in a stout cloth and 

 subjecting it to a pressure by twist- 

 ing the ends in opposite directions. 



(5) Place a layer of cotton wool on a 

 layer of butter muslin. Moisten 

 and remove the superfluous water 

 by careful wringing. 



(6) Fit (5) to the filter funnel with the 

 cotton up. 



(7) Pile the agar (4) on the funnels, and 

 then the funnels are placed in a posi- 

 tion over a series of tiltering tins. 



(8) Place in the autoclave, and autoclave 

 at 120°C. for 1 hour. 



(9) Cool by placing the tins in cold 

 water. The agar sets into a very 

 firm jelly which is cut into slices 

 which are broken up by a meat 

 mincing machine with a very fine 

 bore. 

 (10) Place the small vermicular threads 

 obtained from (9) in trays, and 

 desiccate in a drying oven at a 

 moderate heat. When the threads 

 are dry they have a light brown 

 color. 

 Use: A purified agar. A 1.0% solution of 



the agar gives a clear firm medium. 

 Variants: The threads may be milled into 



a fine powder. 

 Reference: Cunningham (1918-19 p. 561). 



1401. Harvey's Purified Agar. 



Constituents : 



1- Water 200.0 g. 



2. Agar loO.O g. 



Preparation : 



(1) Mix 1.0 part fibre agar, 0.05 part 

 glacial acetic acid and 2.0 parts water. 



(2) Allow the agar to soak in the acidified 



water 15 minutes. 



(3) Remove the fibre agar and wash 



thoroly with water until quite free 

 from any trace of acid reaction to 

 litmus paper. 



(4) Squeeze in a cloth to get rid of excess 



of water. 

 Use: Used in the preparation of media, to 



give a 3% solution of agar, calculating 



from the weight of the agar in the original 



dry condition. 

 Variants : Harvey treated the agar obtained 



above as follows: 



(1) Place the fibre on a filter funnel fur- 

 nished with moistened cotton wool 

 for filtration. 



Note: The filtering wool is sup- 

 ported on butter muslin and the 

 free edges of the latter are turned 

 over the rim of the funnel and tied 

 there. This prevents the wool from 

 sinking down into the narrow part of 

 the funnel and blocking the fil- 

 tration. 



(2) Place the filter funnel with agar in 

 an autoclave over a collecting re- 

 ceptacle. 



(3) Keep one hour at 120°C. 



