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We have used corn meal2 caries in rats for the study of three phases of nutrition in its relation to dental caries, namely, "1) nutrition during the period of formation of the teeth, 2) foods which initiate caries, and 3) factors which affect the rate of progress of decay" (2).Our first use of corn meal caries in rats was in an investigation of rate of decay as affected by foods. Our premise was that regardless of the origin of the lesions, if the corn meal ration was replaced by diets that do not initiate decay, any increase in the size of the cavities would be by a true carious process. In the course of such studies we observed a significantly lowered incidence of decay ("macroscopic" or "fracture' caries as described by others) in rats whose mothers

In a broad study of dental caries in rats, we have required an examination of "fissure caries" as described by Rosebury, Karshan and Foley (1, 2). We have' been concerned with detecting the lesions and describing them as to position and size; examination of the teeth for details of fine structure has been of no immediate interest.Rosebury and coworkers have studied fissure caries in thin sections prepared by grinding but prefer serial sections of decalcified teeth for routine examination. We have devised a method of simultaneously grinding a large number of rat teeth so that fissure caries can be observed and scored in the system used by Rosebury, Karshan and Foley (2). Our method consists of grinding successive parallel planes which are examined by reflected light. In the procedures which are described below, we have aimed at speed of operation, low cost, practical precision and convenience of operation. Sollas (3) has studied fossils by grinding successive planes from his specimens imbedded in wax. Sollas and Sollas (4) dealt with large fossil specimens such as skulls and, of particular interest to us, expedited their work by cutting their objects into several pieces and grinding them simultaneously. Simpson (5) has described a method for precision grinding of successive sections of fossils and Zdansky (6) has employed Simpson's machine with some modification.

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