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In the preparation of nutrient agar the egg process, used to clarify the medium, has always been open to objection on account of the long time required for satisfactory filtration. I would like to suggest a process which I have found more rapid and free from the objections incident to the egg process.
Twenty grams of powdered or shredded agar are dissolved in about 500 c.c. of distilled wateer, by boiling or, better, under about 5 pounds pressure in an autoclave.
Two grams of calcined magnesia are powdered in a mortar and triturated with a portion of the agar solution. When free from lumps, the agar-magnesia mixture is intimately mixed with the remaining agar solution and the whole thrown into a double, white filter and the filtration allowed to proceed in a steam sterilizer or in an autoclave, requiring about three hours for the 500 c.c. to pass through.
THOMSON WF. IMPROVEDD OF PREPARINPREPARIN. JAMA. 1911;LVII(27):2122–2123. doi:10.1001/jama.1911.04260120312005
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