The author made transverse ground specimens of the teeth which had been treated by fluorine, and the attitudes of the fluorine ion were studied histo-chemically.
I) Experimental study on the penetration of fluor ion into the enamel.
Ground sections were made from the human and dog's teeth, which had been immersed in 2 per cent solution of fluoride, and histo-chemical investigation on the penetration of fluorine into the enamel was made by means of Bohmer's hematoxylin staining.
As the results the non-stainable area was observed.
1. Fluor ion penetrated through the organic matter of enamel cuticle, enamel lamelle, rod sheath or cracks.
2. The width of non-stainable area showed a tendency of direct proportion with the duration of staining, but inverse proportion with the increase of age of the specimens.
3. There is the appearance of non-stainable area on the surface of the enamel by application of various fluoride solutions (NaF, NaHF₂, Na₂SiF₆, NH₄F), but no appearance of difference in the degree of penetration.
4, Penetrated fluor ions were not dissolved out from the enamel, namely these ions were fixed in the enamel.
5. At the surface enamel of dog teeth, the non-stainable area could be observed in vivo as well as at that of human enamel.
6. The diluted Bohmer's hematoxylin was discoloured in the test tube by the presence of more than 9 ppm of fluor ion.
II) Acid-resistance of the enamel through which the fluor ion are penetrated.
The transverse ground specimens of teeth which had been immersed in the fluorine solution were put on the Petri dish and acid was pored on them. These specimens were examined histologically. The acid-resistance in these specimens could be assured.
1. The surface, lamelle, caries, and crack of the enamel which were penetreted by fluor ion were clealy distinguished from these of the enamel, namely, by difference of decalcification.
2. At one minute after the specimens were immersed in 5 per cent hydrochloric acid solution, the area penetrated by fluor ion was regarded as a dark part. On the other hand, at thirty' minutes after the specimen were immersed in 5 per cent lactic acid solution, the area was light.

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As the basic investigation of decalcification by EDTA, the author has observed how calcium ion in various materials, e. g., triturated human teeth, bovine bone, marble and fluoroapatite, is removed at varied pH of decalcifying media.
Phosphorus which dissolves simultaneously in the decalcifying media has been also determined.
In summary, the following results were obtained.
1) The modes of the reaction are found to be different in the decalcifying media of varied pH; i. e., second-order reaction in the weakly acid medium (pH 4.3), the first-order reaction in the neutral and weakly basic media (pH 7.0-10.3) . But dentin and bovine bone in these media do not behave as the above unless their organic matrices are eliminated.
From these findings, it is deduced that the decalcifying action of EDTA is disturbed mechanically by the organic matrices in dentin or bovine bone.
Author's conception about the different modes of reaction mentioned above is that EDTA in the weakly acid medium reacts with calcium ion which dissolved out of materials through the acidity of medium, and in the neutral or weakly basic medium it directly attacks calcium on the grains of metarials.
2) In the case of the first-order reaction in the neutral and weakly basic media, the velocity constants of marble, dentin and bovine bone free of their organic matrices, are much greater than those of enamel and fluoroapatite.
In the case of the second-order reaction in the weakly acid medium, the velocity constants of marble and dentin are also greater than that of enamel.
3) In the neutral and weakly basic media, the lower its pH is, the faster the decalcifying velocity becomes. And the weakly acid medium gives a faster velocity, but in this case acid could have the decalcifying action by itself.
4) As to the ratio of removed calcium and phosphorus, it seems that other calciumm salts than calcium phosphates, e. g., calcium carbonate or organic calcium salts, are more soluble than calcium phosphates in the early period of the decalcification.

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The analysis of mucoid isolated from the bovine femur has shown that the amounts of N and amino sugar well agree with that of Eastoe's report, but SO₄″ gives a little lower value.
The ultraviolet absorption spectrum of osseomucoid was found to be very similar with that of ordinary simple proteins.
The contained tyrosine and tryptophan calculated from the ultraviolet absorption spectrum showed that the amount of tyrosine was slightly lower than that was chemically determined by Eastoe et al. and tryptophan gave the value of 0.31% which was not chemically analyzed by Eastoe et al.
According to the study by Tiselius and the filter paper electrophoresis, also in the case of osseomucoid, the Partridge has shown three fractions as shown with the mucoid of cartilage, and it was deduced that they are 1) chondroitin sulfuric acid, 2) probably a kind of protein containing the neutral polysaccharide, 3) something like a compound of the above two components.

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When the acid polysaccharide precipitates with Fe^…, coexisting protein such as serum albumin, if there is any, co-precipitates with chondroitin sulfuric acid. In this case, a small amount of Fe combines also with the protein moiety.
It seems probable that the precipitate produced by the combination of osseomucoid and Fe^… also containes the neutral glycoprotein together with the acid polysaccharide.
Mucoid was precipitated by the addition of Fe^… after the hydrolysis by protease. The determination of N and Fe^… in this precipitate has given a marked decrease of the above two components within 20 minutes from the beginning of the hydrolysis, and the rate of decrease has shown a slight difference between N and If the part of acid polysaccharide combines, as we suppose, much Fe^… while protein holds a little, Fe^… in the precipitate could not decrease so much by the hydrolysis of protein, though the amount of N in the precipitate may decrease as the hydrolysis proceeds.
The above experimental result, contrary to our expectation, is of fairly interest suggesting a possibility of another conception.

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The author studied cases of teeth absence in a family residing in a village which had been maritally isolated for generations due to “caste” discrimination. Radiographic examination reveals that the third molars are absent in 26 out of 29 members older than 8 years of age. Absence of other permanent teeth besides the third molars and some dentition anomalies are found in 12 members, which are listed in detail in the following table.
These anomalies seem to be inherited as an irregularly dominant trait.

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As already reported, the intravenous injection of fluoride solution causes the formation of a characteristic dentin layer in rabbits. But it has been not found the definite mechanism on this and then the author investigated this question by electron microscopy.
Visible changes were recognized when the dentin was etched with weak acid, therefore the detailed structures of the normal and decalcified dentin has been able to proved in electron micrographs.
The fluorine dentin layer has been observated as the decreasing region of acid solubility under the light microscope but revealed nothing by electron microscope. It is believed this reason that the decalcified surface structure of dentin is not different from the normal structure. Namely it is not indicated the fluoride deposits in the dentin fluorine layer.
In future it is advisable to differentiate the crystalline composition of the fluorine layer and the normal layer by electron or X-ray diffraction.

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A kind of removable-plate-fixing appliances with continuous clasps was newly devised and applied to three patients suffering from alveolar pyorrhoea, and its respectable effect was found out upon observing their prognoses for long period of years.
This appliance is, for it removability, so easy to keep it clean as to be free from the dental calculus deposition and considered to be good at the oral prophyractic respect.

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Vital pulpamputation was tried with fibrinogen which was extracted by the ethernol method from a human blood plasma, employing young dog's teeth.
Authors conducted this experiment in expecting that the fibrinogen would check the bleeding and the coagulated blood layer would protect the wound to acquire favourable healing. The results were, however, inflammation or retrogressive change e. g., reticular atrophy of the pulp.

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