The development of lower incisors of white rats (Rattus norvegicus albinus) for each stage of embryonic, newborn, and adult lives was studied. The summary is as follows. 1) At the 13th day of the embryonic life, the oral epithelium lining the anterior portion of the mandibular process has thickened symmetrically on both sides. This is the primitive dental lamina. The lamina extends gradually outer and downwards in proportion to the development of the embryo. The periphery of the lamina is covered by a single layer of short columnar cells, and the inside is filled with cells containing spherical or spheroidal nuclei. 2) At the 14th day of the embryo, the lower free margin of the dental lamina swells roundly to shape the so-called bud stage. 3) From the 15th to the 16th day, posterior portion inside the bud becomes concave to form the so-called cap stage. On the 16th day, however, with progressing development, the posterior end of the enamel cap is separated into two parts, dorsal and ventral. Active cell division characterizes this stage so that the round cells concentrates densely at the central portion of the inner concavity to build the enamel knot which finally assumes the shape of the enamel organ. It is to be noted that a longitudinal streak is seen to traverse along the ventral surface of the enamel cap, which is presumed to have some relation to degenerative process in the dental lamina of permanent tooth. 4. On the 18 th and 19 th day, after further proliferation and increase of depth of the concave surface, the enamel organ forms the bell form. The enamel knot disappears gradually and this stage is characterized by the further differentiation of the cells of the enamel organ, each layer becomes distinct, i. e. the enamel organ consists of the outer and the inner epithelium, the stellate reticulum, and the stratum intermedium. At the same time the dental papilla becomes clear. The outer enamel epithelium arranges on the convex surface of the enamel organ. The mesenchym which is enclosed by the enamel organ consists of the young connective tissue, and the mesenchymal cells which face the inner enamel epithelium become odontoblasts and the dental papilla at this stage shows the figure of the primary pulp. 5. In the period of completion of hard tissue which occurs in the course from the 20 th day of the embryonic life to the 10 th day after birth, the cylinder of enamel organ becomes longer and longer and shows rudimentary shape of tooth. Enamel organ degenerates in turn of inner, outer, dorsal side, except backend and ventral side. The inner and outer enamel epitheliums unite and arrange as a layer of flat cells, and the inner enamel epithelium secretes a thin Haematoxyline stainable layer. But soon after this layer becomes Haematoxyline-unstainable and remains transparent. On the other hand, the ventral side grows further and the pre-enamel is heaped on the pre-dentin. The apex tissue of the dental papilla becomes fibrous and builds bone-like dentin. Pre-dentin and calcified dentin is heaped on the pre-enamel, and this heap is in turn of ventral, inner, outer, dorsal side. A mass of the epithelial cells in the enamel organ neck part remains also in this stage, but it disappears on about 7 th day after birth. The author perceives that this mass of epithelial cells plays the part of inducement of oral epitheliums into deep mesenchymal tissues. 6. In completion stage, the enamel, dentin and bone-like dentin increase in size, and in calcification degree. After formation of the hard tissue is completed, tooth germ begins to erupt. Formation of the enamel and dentin is nearly as well as human, but as 1 mentioned above, tranparent zone is the secretion of the inner enamel epithelium and the cement cannot be seen. 7. The area of the backend of completed tooth shows young enamel organ, but inner, outer, dorsal side of the forward part is about the same with degeneration type

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This study on the morphological traits of head, face and mouth of the mentally deficient criminals was intended to know whether there could be found some hereditary differences from normal traits, and, if found, whether the development of those traits had a relation to the mental deficiency and the crimes. 159 obedient prisoners were chosen as the subject from inmates of a medical prison at a city. Inspections on the tooth health status, and measurements on the head, face and mouth, together with measurements on the plaster casts of the mouth were carried out. The results were compared with corresponding normal values. These persons were inferior to normal in the development of head, face, dental arch and palate. Lack of lateral incisor, abnormal contour of crowns were frequently observed. Increased width of crown in central incisor and canine was noted. Also V-formed dental arch was frequently met. This was probably related to a characteristic physiognomy of the subjects which comparatively more acute median angle of closed upper and lower lips had contributed, when viewed from lateral direction. Whether or not differences in these traits had derived from developmental disorder of head and cranium, and whether these traits showed the presence of hereditary types of criminal, or it only dealt with the manifestations of acquired traits, were not yet reached from the present study. These are themes to be discussed elsewhere in the hereditary study in twins. At present it may be safely said that these manifestations of the characteristic traits would not warrant identification of mental patients or criminals.

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The authors conducted a histological study on the connection of tooth cementum and culculus. The results are as follows ; 1. Five modes for the attachment of the culculus to the cement surface are recognized. 2. It was revealed that the difficulty or ease in removing culculus might be dependent upon the modes of attachment.

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A total of 60 teeth from the corpses of tuberculous patients at the National Sanatorium in Fukuoka were examined patho-histologically and the findings is as follows. 1. In no case was any sign of tuberculous lesions found in the teeth and the surrounding tissues. 2. Among the pulpal involvements, degenerative lesions, espesially pulpal atrophy of notable severity were observed. 3. Vaso-dilatation and rarefaction of the surrounding tissues were in many cases observed. 4. Thinning of jaw bone trabeculae also occurred frequently. 5. In the gingival region, ulcerative lesion with destruction of gingival papillae occurred fairly frequently.

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It is often observed that tooth contact point develops through physiological ear a surface form rather than a small dot. Hence, it may be as well called tooth contact surface. In its full development, the contact surface extends as wide as approximately 4 square m. m., so that the types of contour which it assumes can afford to be classified simply by naked eyes. 306 out of 686 teeth were chosen on the basis of easy identification of individual tooth and clearness of the contact surface, and these were classified into seven types, i. e. first cocoon, 2nd round, 3rd oval, 4th dean, 5th heart, 6th double, 7th triangle. In the present study the occurrence of these 7 types were examined for each tooth kind. For all kinds of tooth, the contact surface of the 3rd oval type was most frequently observed, followe dy 2nd round type and 4th bean type. The bean type was rarely met in anterior teeth. The 7th triangle type was rare in molar teeth, The Ist cocoon type, 5th heart type and 6th double type were met occasionally in molar teeth, but least in anterior teeth.

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We described in this article 1) the outline of studies on the electrical phenomena of salivary glands, 2) the action potential elicited by stimulating the chorda tympani and the sympathetic nerve, i. e. chorda electrogram and sympathetic electrogram, 3) analysis of the action potential to its components, which were advocated by several authors in different way, 4) the variation of the action potential in its form and size by changing the stimulant factor, 5) the effect of drugs, especially the poisons for automatic nervous system, on the action potential, and finally 6) the relations among the action current, the electrical conductivity and the salivary secretion of the glands. Fig. 1. Fluctuations in secretion, volume-flow of blood and electrical deflection elicited by prolonged chorda stimulation (Gesell). VF : volume-flow of blood, BP : blood pressure, S : secretion, T : time and stimulation, E : electrical deflections. Fig. 2. Action potentials of the submaxillary gland of cat (Langenskiold). a) Chorda electrogram, b) Sympathetic electrogram. P : action potential, S : secretion, N : nerve stimulation. Fig. 3. Analysis of chorda electrogram. P : positive component potential, N : negative one. Fig. 4. The action potential by the combination of chorda and sympathetic stimuli (Langenskiold). a) Sympathetic stimulation during the chorda stimulation and vice versa. b) The effect of chorda stimulation during the off-response of chorda electrogram. c) The similar experiment as above, under the action of Eserine. P : potential change, CS : chorda stimulation, SS : sympathetic stimulation, S : secretion. Fig. 5. a) Relation between the size of off-response in chorda electrogam and the duration of stimuli. b) Variations of chorda electrogram by changing intensity and frequency of stimulation. P, S and CS are the same as in Fig. 4. Number denoted on the left side shows the distance between induction coils and that on the right side the frequency of the induction shocks. Fig. 6. Action current and velocity of secretion in human parotid gland elicited by gustatory stimulation (Iwama and Shinjo). a) normal control, b) under the passage of electrotonic current. P : potential change, S : secretion. Arrows denote the administration of 10 % NaCl (a) and 10 % acetic acid (b). Fig. 7. Changes in secretion, electrical resistance, electrical potential and acidity of the venous blood by chorda stimulation (Bronk and Gesell). S : secretion in drops, ST : stimulation of chorda by 1 volt A. C., E. R. : electrical resistance, E. D. : electrical deflection, T : time in 15 seconds, 1 : occlusion of Wharton's duct, 2 : deocclusion of the duct.

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The pioneer works of Hunt, Hoppert and co-workers on the inheritance of caries susceptibility and caries resistance in albino rats were reviewed. Though the publication of these works extended over more than twenty years, only those articles from 1948 to 1955 were able to be cited by the author owing to unavailability of their earlier works. This paper is intended to make an integral part of a review of American literatures dealing exclusively with the etiology of dental caries.

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