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EXPERIMENTAL Shibata states that he reared young rats on a diet consisting of "whole" rice and greens, plus 5-10 percent of various carbohydrates, of which dextrin and maltose were most effective in producing caries. The lesion, he states, developed in the molar fissures in about twenty days, and destroyed the crown in a week. Our first experiment was an attempt to repeat this finding. The animals were the Long-Evans strain of hooded rats, originally given to us in March, 1930, by Prof. P. E. Smith of the Department of Anatomy, and since bred by ourselves on a modified McCollum stock-ration (9). Full litters were distributed among the experimental groups in all cases at weaning, twenty-two days after birth. All animals were weighed every five days. Diets, other than spinach, were fed ad lib.Group I. Four litters, comprising 22 animals, were placed on Diet 1: Brown rice ("Comet"), unground, 92 (percent); white-potato dextrin, 8;

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In the first report in this series (20), it was noted that enamel hypoplasia occurred in incisors of rats on a low-Ca vitamin-D-free diet, but that apparently only recently formed enamel was affected, molar teeth escaping the deformity. The emphasis placed by Mellanby (15) on possible relationships of enamel defects to dental caries suggested the desirability of attempting to produce defective molar-enamel in rats by dietary means. Since enamel calcification of rat molars is complete at a very early age, it appeared desirable to feed a deficient diet to mothers during pregnancy and lactation, and then to continue the young under the same dietary conditions. Dental effects of this and other conditions, embodying possible factors in caries etiology, form the basis of the present report. EXPERIMENTAL METHODSThe plan followed in these experiments is represented in table 1. The first letter in the "designation" (last column) indicates the mother's diet; the second and third, the diet of the young after weaning.2 One group of mothers (N) was maintained on an optimal diet to provide a normal standard of growth and tissue structure. Of the groups on the basal test-diet,

and probably other factors of the vitamin B complex for norma: growth under the conditions of these studies. Possible factors altering the requirement of choline for dogs on synthetic rations are discussed.The characteristics and properties of the so-called commensal spirochetes of mucous menibraiies, and their individual or contrihuting rbles in fuso-spirochetal infections, remain inadequately understood largely because of a lack of effective nieans for their isolation and maintenance in pure culture. Treponema vimenti, the large delicate loosely wound spirochete of the mouth, seems never to have been obtained in pure culture; 7'. buccale, the large? thick, loosely wound form, has been reported in culture rarely,'. 2* apparently under conditions which could not be duplicated. T. ,microdentiurn, the small mouth spirochete which resembles T . pallidurtz in morphology and is cultivable with the least difficulty,*-* seems for that reason to be the only member of the group which can be accepted with little doubt as a distinct species. Studies of pure cultures of T. microdentkn, moreover, have yielded interesting information on the pathogenesis of fuso-spirochetal infection^.^? 6p ' 9On the other hand, none of the other varieties which have been described and named, such as Noguchi's T . ynncrodentiim~~ or the several species named by Seguin and Viiizent," is so clearly defined.