The localization of the gustation center was investigated in white rats by examining the results of the preference method and the electrical response of the cerebral cortex to chemical stimulation of the gustatory end-organs. An objective observation and quantitative measurment of the acuity of gustation of white rats by the preference method were effected by the use of a liquid supplier, a graduated test tube, devised for the purpose by Hirakawa and Ueno. The first step in the first experiment was the determination of the gustatory threshold for each test solution by the preference method; and the next the symmetrical destruction by bilateral operation of one small area of the cerebral cortex, for observation of the postoperative change in the taste ability of each animal deprived of the local cerebral function, and for eventual identification of the area of the cortex concerned in gustation. The results of this experiment in 45 cases led to the conclusion that the destruction of a certain small area of the lowest portion of the parietal lobe, lying near where the frontal lobe meets the temporal, is invariably followed by an enduring drop in the gustation threshold, i. e., permanent gustatory impairment. The other experiment, performed alongside of the first in the hope that the result might throw some sidelight on the problem, was an examination of the accompanying electric phenomena produced in the cerebral cortex by gustatory stimulation. The result of this experiment showed that the electrical effect of gustatory stimulation on the cerebral cortex was divisible into : (1) inhibition of α waves and (2) multiplication of β waves and an increase and periodic appearance of attack waves. The former change appeared over a fairly extensive area of the cortex and the extent of the area where the change could be induced was not finally definable. Whereas the latter changes (2) were demonstrable exclusively in a limited area of the cortex, an area embracing in the center the lowest portion of the region identified as the gustation center in the first experiment, indicating presumably that the changes are manifestations of a central nervous excitation caused by gustatory stimulation. Experiments in electric stimulation of the cerebral cortex showed that the area of the cortex where the latter changes (2) could be induced to the utmost extent was identical with the area controlling the movements of the mouth and jaws. This was also the very area where the changes in the cortical brain wave associated with the movements of the lips, tongue and jaws are inducible to the highest degree, and what was more, these changes bore a close temporary resemblance in the shape of wave to those (2) induced by gustatory stimulaton. The results of the foregoing two experiments coincide with each other in locating the gustation center in one identical area of the cerebral cortex. It is therefore conceivable that in white rats the gustation center is located in a small limited area of the lowest portion of the parietal lobe, abutting on the boundary line of the frontal and the temporal lobe. It is also presumable that the cortical taste area may be either identical with, or located in close proximity to, the sensorimotor area for the mouth, tongue and jaws.

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The animals used were 40 rats and the method adopted was het "Preference method" using a liquid supplier, a graduated test tube, devised by Hirakawa and the author. Gustatory threshold and gustatory function were first measured in normal rats by the preference method and the two gustatory nerves entering the tongue, the glossopharyngeal and the lingual nerve, were next cut operatively. The measurement by the preference method was resumed after the cutting and was continued thereafter and the following conclusion reached : 1. The cutting of the gustatory nerves was followed by the disappearance of almost all taste-buds under their control. a. The papilla near the apex of the tongue was the first to disappear. b. The disappearance of cells in each taste-bud seemed ascribable to the destructive or lytic changes of the nuclei and not to any inflammation. c. Gustatory cells degenerated and disappeared faster than sustentacular cells. d. The vacant space left after the disappearance of taste-buds appeared to be filled up by the surrounding epithelial cells. 2. The regeneration of taste-buds was seen in one case 26 days after the operation and in all 32 days or more after it. a. The rudiment of each regenerated taste-bud was formed by a change of o epithelial basal cell. b. The time for taste-buds to be regenerated, unlike that for their degeneration, was not fixed for each particular area they were located in. c. The restoration of papillae was not always concurrent with the regeneratino of taste buds. Taste-buds in different stages of develoment were to be seen in one identical papilla. 3. Experiment in gustation (by preference method) a. Preliminary I Gustation threshold for quinine hydrochloride……0.001% II Gustation threshold for hydrochloric acid……0.005% III Gustation threshold for saccharose……0.3% IIII Gustation threshold for sodium chloride……0.05% Each rat gave a well-regulated threshold curve for a given taste solution despite its likes and dislikes. b. Time for the degeneration and disappearance of taste-buds. The rejection threshold was raised for quinine hydrochloride and hydrochloric acid and the acceptance threshold lowered for saccharose and sodium chloride. Moreover, the amount of the taste solution drunk in was subject to the manner it was taken in, confused or wanton. However, the threshold curve was brought back near to normal as the taste solution was raised in concentration. Presumably those small number of pharyngeal and epiglottic taste-buds which are under the control of the vagus or some other agents than taste-buds are concerned in such approximate normalization of the threshold curve. c. Changes following regeneration of taste-buds. In animals with taste-buds regenerated, taste ability became restored, the taste solutions were taken more regularly, and the threshold curve approached the normal level, in proportion to the number of regenerated taste-buds.

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With the object of studying the heredity in the anatomy of mouth we investigated the inhabitants of Iwaijijma, Kaminosekimura, Kumagegun, Yamaguchi prefecture from dental view point. The results is summarized as follows. 1. The rate of consauguinous marrige among the islanders amounts to 87%. The distribution of A B O blood forms differs from the neibouring inhabitants in the fact that O form exclusinely predominates. 2. The distribution of finger print resembles to that of opposite town, Kugamachi, Yamaguchi prefecture. 3. Physical abnormities and psychosis by heredity are much observed. 4. Four cases of palate fissiure and hare lip were found. The type of incisal occlusion was psalidodontie in 80%, and lower jaw was in the most case paraboloid. 5. The countenance of the inhabitants resembles much with each other. Abnormities of dental arch were not observed. 6. It was noted that the abnormity of lateral incisor was found in 6%. 7. Carabelli's cusp was fairly abundant. 8. Dentition of permanent teeth was comparatively premature.

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For the purpose of studying the tooth erosion by acid, the author has investigated the teeth of a factory laborers in North Kyushu, and has carried out a series of experiment concerning the protecting measures against the tooth erosion by acid The results are as follows;- 1. The percentage of laborers suffering from the tooth erosion is twenty six among fifty six, namely fourty percent. 2. It was confirmed that the longer the service years the higher the rate of the patients. 3. Percentage of dental caries, average number of existing teeth, and health index of first molar are respectively worse in the member suffering from the acidic erosion as compared to the healthy member. 4. Average number of eroded teeth is 4.45, and the major part of the tooth number attacked by the erosion was occupied by central incisors, becoming fewer toward posterior teeth. 5. The shape in which the tooth was attacked by the erosion varies according to the types of individual incisal occlusion. 6. Experimentally, extracted teeth were exposed to the acidic air of the factory to know how tooth enamel is dissolved. Dissolution of enamel began in four experimental hour and progressed thereafter. The enamel exposed to acidic air showed a rough surface, while the enamel of the tooth immersed in water remained smooth. 7. For the protection against acidic erosion, ammoniacal silver nitrate was the most advantageous to which succeeded silver flouride and silver ferrocyanate. From the above stated data, a few prophylactic measures will be better adviced. a) Prevention of acid leakage. b) Dilutin of acidic air through good ventilation. c) Hygienic management of factory environment. d) Individual sanitation, routine removing of tooth plaque and deposition. e) Prohition of talking during work, cleansing of mouth after meal, use of alkaline gargle. Use of gas mask are most advisable which will be substituted simply by using gauze mask immersed in bicarbonate of soda solution. Or give chewing gum containing ammonium salt and fluoride for the purpose of neutralizing saliva and cleansing mouth. f) We are convinced that the disease will be supressed in some extent by hardening the tooth enamel through the coating of ammoniacal silver nitrate or silver fluoride. The most efficient is to apply to the tooth crown once a month the Neo-Fluorigen which is consisted from two parts of natrium-fluoride, one part of celluloid, and Ioo part of amylacetate.

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1. The author reports that the dentition of permanent teeth in the children of hot spring region is earlier than that of other regions. 2. The time of permanent tooth dentition in Beppu city reported by the author is earlier than that of the children in Tokyo reported by Okuie. 3. Dentition was earlier in male than in female children. 4. There is a correlation between the dentition and V.W. index.

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For the purpose of studying the mottled teeth in Kyushu, 4254 children from 6 to 15 years old resing in Kumamoto city, and Tagawa and Yame region of Fukuoka prefecture, Aso region and Kitamorogata region of Miyazaki prefecture were investigated. The result were as follows, 1. The percentages of individuals infeced with mottled teeth were 52% in Aso region, 44% in Kitamorogata region, 23% in Yame region, 17% in Kumamoto city, 10% in Tagawa region. 2. Caries rates, averages of caries number, caries index, D.H.C. of first molar were found to be inverse to the percentage of mottled tooth infection, tooth health herefore being best in Aso region and worse in the order of in Kitamorogata, Yame, Kumamoto, Tagawa region. 3. The intensity of infection by mottled tooth was most clearly observed in Aso, diminishing in the order of in Yame, Kumamoto, Tagawa. 4. As the rate of mottled tooth infection between each tooth the upper front teeth were the most predominant and the upper teeth were generally more frequently attacked by the disease than the lower teeth. 5. Mottled tooth manifested itself in the most case on the whole tooth crown, then in the order of at the cusp, at the centre part of the crown, and at the neek, 6. Fluoride contents of drinking water 2.7 P.P.M. in Aso, 0.7 P.P.M. in Kitamorogata, 0.4 P.P.M. in Yame, 0.02 P.P.M. in Tagawa respectively.

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On August 1950, I examined and treated number of dental caries and time of dental eruption of permanent teeth of the boys and girls of primary, secondary, and high school of Takane and Kamihata Villages in Yamaguchi Prefecture, and I obtained the following results. As to actual number of teeth in each year of age generally in which female children are greater number than male. and actual number of permanent teeth in each of age also female children are greater than male. As to rate of the dental caries female children from 7 to 9 years of age are greater than male and another years of age male children are greater. In whole materiell rich rate of dental caries are 48 percents, and it seems to be less than another quaters. The caries late of 1st permanent moler seems to be less than in Tokyo, by Higaki (1949). The time of dental eruption of permanent teeth seems to be later than in pre-war condition and earlier than in Tokyo City by Okuie (in 1948)(Author's abstracted).

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Physical status of eighty five thousand nine hundred eight youngsters of primary, middle and high school in Miyazaki Prefecture in 1945 and 1948 were examined. The results will be summarized as follows 1. The provincial groop whose amelioration of the physical status between these year period was most evident was that of Higashiusukigun to which succeeded those of Nishimorokata gun, Minaminaka-gun, Miyakonojo-city, Nobeoka-city and Miyazaki-city. It was concluded that the suburban groops were faster in returning to the prowar status than the city groops. 2. In 1945 the physical status of Miyakonojo-city groop was the best to which succeeded the groops of Higashiusuki-gun, Minaminaka-gun, Miyazaky-city, Nobeoka-city, Nishimorodata-gun. It was generally noted that the physical status of city groops excelled that of suburban groops, and male groop excelled female groop. 3. In 1948 male groops also excelled female groops. 4. Improvement of dietary custom, increase of dietary allotment or giving the youngsters the complete school rations are to be advised for the city groops, the author thinks.

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