It has been shown that enzymes in serum will change maltose, dextrin, and starch so that they will react as dextrose in media. These enzymes are destroyed by heating to 60°C. for 15 minutes, but they are present in sera that have been refrigerated for as long as 18 months. The practice of using carbohydrate media containing unheated serum should be discouraged, and if it is used the possibility that the carbohydrate may be changed by the enzymes present must be considered.

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