Dental examination has been conducted on a total of 4794 youngsters of both sexes ranging in age from 6 to 15 residing in Mimata-machi along the river Hagihara, in Yamada-machi along the river Marutani and in Nishidake district along the river Yasunaga, all with approximately similar socio-economic condition. Endemic study was also undertaken on the physico-chemical constituents of the soil and the river water, domestic trades and amount and quality of food consumed by each subject per week with special reference to the incidence of dental caries. Results obtained were summarized as follows. Dental decay was found most abundant in Nishidake district, followed by Yamada-machi and Mimata-machi in decreasing order. The socio-economic status of the inhabitants was richest in Mimata-machi, followed by Yamada-machi and Nishidake district in decreasing order, demonstrating an inverse relation with the dental caries incidence among three distrits. Of various reasons conceivable for the difference of caries rate among these people, the most probable one was the relatively high concentration of SiO_2 among the mineral components of soil and water examined, since silicon dioxide are believed to disturb normal calcification of the tooth.

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A field study has been undertaken on the selected groups of public school pupils residing under similar environmental conditions in the suburban communities of Miyakonojo city, Miyazaki prefecture, with special reference to the status of tooth exchange. 1. The earliest shedding of deciduous teeth and likewise earliest eruption of permanent teeth were observed in the group of Mimata-machi, followed by those of Yamada machi and Nishidake district in this order. 2. Reflecting individual geographic situations of the communities, 58% of the plainsmen in Mimata-machi, each 77% and 81% of the highlanders of Yamada-machi and Nishidake were respectively engaged in farming as the chief means of living. 3. Study in physical and chemical analysis of the water and soil in the respective area as reported by us elsewhere, failed to reveal any significant connection with the data obtained on the tooth exchange in the present report. 4. The geographic situation of individual communities might have had some influences on the rate of acceleration of tooth exchange in these subject groups. It may be, however, almost negligible as compared to nutritional conditions or certain difference in the dietary habits of respective peoples in so far as this particular phase of tooth development is concerned.

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Although nutritional requirement for culturing individual lactic acid bacteria has been extensively studied, some of the fastidious member of the family often fail to grow on media of ordinary composition. Laboratory need has prompted us to an attempt to develop a single medium simultaneously supporting as widest possible range of those organisms routinely used in the microbiological assay and other nutritional study. A tentative medium made in this laboratory combining Rogosa's SL agar and tomato agar has proved not only promissing for the purpose, but also to serve as another type of selective medium supporting more uniform growth of those organisms which poorly grow on SL agar. The composition of the medium consisted of 0.5 to 1.0 gm peptone, 0.5gm yeast extract, 0.5gm lactose, 1.5 gm glucose, 1.5 to 2.5 gm sodium acetate, 0.1 gm tween 80, 2.0 gm agar and 30ml tomato juice to a total volume of 100ml with distilled water, pH adjusted either to 6.5 or 5.4 according to maintenance or selective use. The organisms tested included accepted pure cultures of 14 species of lactobacilli and two species of streptococci. A series of salivary lactobacillus counts on SL and the present media was also conducted. It was revealed from the preliminary study that of the ingredients of both media the principal agent responsible for characteristic inhibitory action of these media was acetate in the amounts used and not phosphate, citrate or mineral salts as included in SL agar, the lowered pH being secondary in the role. The same acetate was found also inhibitory to some extent for several heterofermentative and streptococcal organisms. However, the present medium exhibited moderate but more uniform growth of all the lactobacilli tested and, although not yet conclusive, with apparently the same selective ability as SL agar.

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