A NOTE ON THE PREPARATION OF AGAR AGAR 

 CULTURE MEDIA 



C. L. WILLIAMS AND H. P. LETTON 



United States Public Health Service 



One of the greatest troubles in preparing agar agar is clearing 

 the medium. Filtering through paper is very slow and requires 

 a special water jacket for the filter in order to keep the agar hot 

 enough to prevent sohdification. Nor does a paper filter entirely 

 clear the agar. The more usual method of filtering through 

 cotton requires repeated filtration, and even then seldom gives a 

 perfectly clear product. 



The principal cause of failure is apparently the presence of 

 finely divided insoluble particles derived from the agar agar, 

 which become evenly distributed through the medium after this 

 substance has been dissolved. These particles are often so fine 

 that a great part of them will pass even through filter paper. 



In the laboratory of the Sanitary District of the Great Lakes 

 various methods were tried to facilitate filtration while securing 

 a clear product. The use of egg albumin as a coagulant in some 

 media suggested coagulation as probably successful, and the use 

 of the Hygienic Laboratory method of preparing Endo's medium 

 gave us the clue to the present procedure. 



In the Hygienic Laboratory method for Endo, the medium is 

 partially cleared by pouring into large beakers while hot, where 

 it is allowed to cool and harden. On inverting the beakers the 

 solid mass of agar slips out, and the bottom where most of the 

 suspended matter has settled is cut off and wasted. This proc- 

 ess was modified by us in the case of ordinary agar media by 

 placing the container in a large water bath (a large saucepan usu- 

 ally served for this) which was kept over a low flame for several 

 hours, usually over night. This procedure caused the collection 

 of the suspended matter into flocculent masses which settled to 



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