Attempt to measure the efficiency of human mastication on a quantitative basis is an important task assigned to dentistry to which many workers have contributed. These studies, however, have been done in vivo on human or animal mouth where various factors involved in the mastication and their iudividual effects on its efficiency could not be clearly understood. The author attempted to study the specific effect of these factors by making a model apparatus for the grinding mechanism of mastication. It is hoped that by this apparatus the three major factors, as the author arbitrarily enumerated, i. e. masticatory pressure, occlusal surface, and food carrying action besides other factors such as duration of chewing and amount as well as nature of saliva may be studied independently as to their effects on the efficiency of mastication. 1 MODEL APPARATUS OF MASTICATORY GRINDING The masticatory pressure of human individuals was recorded osillographically (Fig. 4), and a press machine equipped with a pounder exerting the same operating load was devised. This machine was conneted with a kymograph to make automatic recording of the pounder's movement. When necessary, the machine afforded to make alterations in the contact surface of the pounder and the state of food migration. The set of these equipments is shown in Fig. 3. 2 EXPERIMENTAL The grinding tests in wet and dry processes were done on peanut, raw rice and dried rice. In the wet process of grinding, load equivalent to 2.2 kilograms, in the dry process, load equivalent to 5.8 kilograms were applied on the pounder having the standard surface of 1 square cm.for each pounding, and 25, 50, 100, 200 and 400 times of pounding were respectively carried out. The particles of the materials obtained by each test were divided in portions by 8, 10, 28, 48, 100, and 200 mesh sieves successively. Since the author had been aware of the imperfectness of the sieving procedure hitherto commonly used, he has newly prepared an apparatus by which each stage of sieving was carried out simultaneously in water. On this apparatus the food particles in each mesh sieve were impregnated in water and agitated 3000 times automatically and successively. The particle distributions obtained from the above mentioned procedure showed the following results. 1) In peanut grinding, it was noted that considerable weight loss of the material occurred due to diffusing away of the peanut oil which occupies 20 to 30 percent of the material. The loss had been supposed by previous authors as due to swallowing down of fine particles by mouth experiment. The author confirmed that this is not the case, and therefore, data from these mouth experiments on peanut would be far from representing the masticatory efficiency. Besides the disadvantage, peanut undergoes remarkable denaturation in the water, and not at all suitable for the experiment as the test material, 2) As test material, dry and wet rice had similar nature to peanut. Rates of oil diffusion and water dissolution were small, but denaturation by water was not negligible in these materials. Both were better than peanut but not sufficient. 3) The particle distributions obtained in peanut and rice experiments do not seem to conform to the exponential law of Rosin and Rammlar as well as to the probability law of Austin. 4) The author plotted the correlations between the particle distributions and the amounts of work done in grinding the materials, and from the graphs, it was believed, the efficiency of grinding would be quantitatively known by examining the particle distribution of the material.

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The three major factors associated with oral mastication are, according to the authors' opinion, the masticatory pressure, the occlusal surface and the action of carrying food into proper position by the tongue and other oral muscles. The effects of this carrying action by muscles on masticatory efficiency were examined by means of a grinding test machine, specially devised by Yokota, one of the authors. The particle size distribution obtained when the machine was allowed to grind equally sized food particles was compared with that obtained when the machine was provided with unequally sized particles, and the results were shown in Fig. 1. and Fig. 2. From these data it was revealed that the carrying action exerted unequal effect upon the particles so that the larger particles were preferencially carried and grinded. Hence in measuring masticatory efficiency, hitherto adopted method of calculating amount of over size of the larger sieves only, should be re-examined as to its validity.

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6311 subjects ranging in age from six to fourteen were studied statistically concerning the relation between physique and the eruption time of permanent teeth. The subjects were divided into three groops of big, medium and small sizes on the basis of body measurements in each age and sex groops. The numbers of teeth erupted were compared between these groops, and the following results were obtained. 1. Those who had excellent physique had more teeth erupted. This indicates that their teeth erupted earlier than did the teeth of inferior physique. 2. The data on height, weight and chest girth in the physique of the subjects examined had a slight correlation with the numbers of teeth erupted.

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To add to a series of the anatomical works of Saegusa, a study was performed on oral glands of Takydromus tachydromoides, and the summary is as follows. 1) Gldd. linguales, Gldd. sublinguales and Gldd. labiales inferiores were found to be present in the mouth of Takydromus tachydromoides, the numbers of which were of medium order between the corresponding glands of Eumeces latiscutatus and Clemmys japonica. 2) The contours of these glands resembled to the corresponding glands of Eumeces latiscutatus and Clemmys japonica, i.e., a) Gldd. linguales lie superficially on the dorsal and lateral side of posterior parts of tongue, b) Gldd. sublinguales are consisted of groops of tiny glands encircling from anterior toward root of tongue in V form, and are vaguely differenciated into Gldd. sublinguales laterales and Gldd. sublinguales mediales, c) Gldd. labiales inferiores forms a nrrow band consisting of groops of tiny glands which lies along the outer side of the mandibular process. 3) The properties of the cells of these glands, same as those of Eumeces latiscutatus, are mucous in Gldd. linguales, mixed serous and mucous in Gldd. sublinguales and mucous in Gldd. labiales inferiores. 4) As the single cell gland, goblet cells occur in number on the epithelium lining the posterior parts of the mouth, also same as in the case of Gekko japonicus. Eumeces latiscutatus and Clemmys japonica.

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2589 subjects of both sexes from 18 to 60 years of age, of which 2355 belonged to male and 234 belonged to female, were studied as to the tooth health in each age and sex groop, and the results obtained were statistically analized and summarized as follows. 1) Caries incidence rate, average caries number and average caries index rose with increasing age, while average dental health index of first molar fell with increasing age, Female groop was worse in every point examined. 2) Caries incidence rate in the dentition : in both sexes the rate is higher with anterior teeth and first premolar in upper jaw, with molars, however it is higher in lower jaw. The rate is higher in female groop than in male groop. In both sexes the caries incidence rate of first and second molars was highest, that of lower canine tooth was lowest. 3) The rate of missing tooth : in both sexes the rate is higher with anterior teeth and first premolar in upper jaw than with corresponding teeth in lower jaw, while with posterior teeth the rate is higher in lower than in upper jaw. Among all dentition the missing rate of the lower first molar was highest, that of the lower cuspid was lowest. 4) The rate of filled tooth : the rate rose with increasing age, and was highest in upper anterior teeth in both sexes. In male groop the percentage distribution of the kinds of tooth restoration was as follows : metal crown 85.92%, inlay 8.40%, cement filling 3.54%, amalgam filling 2.14%. The rate of filled tooth was 6.00% in male groop, 6.85% in female groop. 5) D.M.F. rate in the dentition : the rate was higher in upper than in lower jaw with anterior teeth and first premolar, while with posterior teeth the relation was reverse. In both sexes the rate was highest for first molar and lowest for cuspid. The rate was higher in female than in male for each tooth mentioned. The rate rose with increasing age.

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A total of 7243 children of kindergarten and primary school were examined concerning the possible relation between the dietary habits and the character, mental faculty and the degree of fatigue. The number of those adhered to obviously unbalanced diets amounted to 56.8% of the total among which female member slightly preceded male member. Dividing these member by the preference either to meat or vegetable diets, it was distinctly noted that a large number of adherents in the meat diets were found especially in the female children of older ages. Many fatigued individuals were found in kindergarten children with unbalanced diets. However, difference in the degree of fatigue found between those members with normal and unbalanced diet habits disappeared as they had reached the stage of primary school. It was generally observed that lack of endurance to physical exertion, lack of friendliness, and certain impaired character patterns have resulted from the unbalanced diet habit of the children. It was presumed that these unfavorable effects would have close relation to the specific propensity for individual kinds of food they took.

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