Five isoenzymes of LDH have been isolated from normal human gingiva, and some properties such as optimum pH, substrate inhibition, heat stability were studied.

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In 1963 the present author had investigated in detail through electron microscopy the enamel regions around the pits [1]. As a consequence, a conclusion was drawn that most of the enamel areas around the pits, in particular those close to the frequent floors of the pits, are made up of rodless portions of enamel. He stated that distinction here is quite difficult to make in most cases between enamel rods and interrod substance due to a considerable hypomineralization.
The pits and fissures have been generally held to be portions which will be most easily affected by a carious lesion. However, most of their histological examination has been done by means of ordinary light microscopy and except for AWAZAWA'S description on the pits, there is no availab'e research result touching on the occlusal fissures made by electron microscopy. Therefore, an electron microscopical investigation on the enamel around the fissures is full of interest, as it helps our understanding of histologic peculiarities of the enamel portions adjoining the floors of fissures.
The present study is designed to make clear the enamel areas adjacent to the occlusal fissures, especially those hypomineralized enamel portions descending to various extents from their floors toward the amelo-dentinal junctions, examined in detail by the electron microscope. Through this research, he could secure some interesting images from these portions.

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