The fermentability or non-fermentability of a given sugar is a question which must be constantly decided in the classification of bacteria. Because of the number of sugars and often the larger number of cultures involved, the bacteriologist usually resorts to indirect methods to determine his decision. Turbidity of the media, gas or acid production are the usual criteria taken to indicate fermentation. Everyone realizes that these indirect methods are uncertain and often misleading. Some bacteria produce little or no cloudiness in the media, large numbers produce such small quantities of gas that it cannot be detected except by very refined methods, and others convert most of the sugar into neutral products, such as ethyl alcohol, mannitol, acetone, etc. (Stiles, Peterson and Fred, 1925; Reilly, Hickenbottom, Henley and Thaysen, 1920). In many instances fermentations are best made with an excess of CaCO8 and in such cases gas and acid production are excluded as a means of determining fermentability. In a recent study of anaerobic bacteria Brown (1925) emphasizes the difficulty of determining the fermentability of sugars by indirect methods. A direct method of measuring the sugar destroyed is much to be preferred. It gives a definite and accurate measure of the fermentability of the sugar. Such a method to be widely used must be quick and fairly accurate. The gravimetric methods