Acute toxicities of fresh FC and stale FC which were stored in three conditions for three years were studied with use of male mice of ddY strain, weighing 18.0-22.0g. The test animals were fed on a solid diet and given tap water freely, but were starved for 20 hours prior to the test. Each drug was diluted in olive oil to be administered orally in the dose of 0.1ml/10g. Daily number of mice died and body weight of survivers were recorded for 7 days. LD_<50> was calculated by Litchfield-Wilcoxon's method. Results were as follows : 1. LD_<50> was 1600 (1380-1860) mg/kg for fresh FC, 1600 (1390-1840) mg/kg for stale FC stored in sealed ampoules at 5℃, 2100 (1740-2540) mg/kg for stale FC stored in sealed ampoules at 40℃, 1150 (960-1380) mg/kg for stale FC stored in lidded containers at room temperature. 2. The ratios of toxic potency to fresh FC were 1.0 for stale FC stored in sealed ampoules at 5℃, 0.8 for stale FC stored in sealed ampoules at 40℃ and 1.4 for stale FC stored in lidded containers at room temperature. 3. The restraint of growth was observed in each surviving mouse administered one of the drugs, and it was most noticeable in the mice administered stale FC stored in lidded containers at room temperature.

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It is generally acknowledged that masseter muscles take a great part in occlusal stability after bite opening, a means used in orthodontic treatment. Various studies of adaptation of masseter muscles have been done from different standpoints. Histological investigations however have been limited in number. An experimental investigation of adaptation of masseter muscles therefore has been done from the standpoint of finestructure. The experiment on increasing intermaxillary distance was conducted with use of anterior bite plate (Experiment I) covering only the maxillary anterior segment and complete bite plate (Experiment II) covering the anterior and posterior segments in 21 adult dogs (mongrels) for one, three, and six months. The histological and electron-microscopic findings were as follows : 1. In both Experiments I and II, muscle fibers of the masseter muscles were thinner than the normal ones in width after one month. Arrangement of the muscle fibers zigzagged. Electron-microscopically, ruptures and disappearances were observed in myofibrils in part of Z-line and I-band. Most glycogen particles disappeared. The changes in myofibrils seen in Experiment I were not observed in Experiment II. Many instances of swelling and vacuolation of mitochondria were observed. The degree of vacuolation however was slight. 2. In both Experiments I and II in the third month, most muscle fibers were thicker than those in the first month although some were still thin in part. Electron-microscopically, more significant ruptures and disappearance were observed in Z-line and I-band of myofibrils. Glycogen particles decreased as in Experiment I in the first month. 3. In both Experiments I and II in the sixth month, the width of the muscle fibers on the whole was restored to that of the normal ones. Electron-microscopically, myofibrils and mitochondria tended to be restored to near normal. Glycogen particles showed a trend toward restoration to normal in Experiment I but remained disappeared in Experiment II. 4. In both Experiments I and II, the length of sarcomere increased with time. The length of I-band in particular showed a marked increase. Based on the foregoing finding, the finestructure indicative of complete adaptation was not observed. The experiment however suggested at least a need for a longer retension of bite plate in performing the orthodontic treatment of increasing intermaxillary distance to patients who have passed the growth period.

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Immature permanent teeth, numbering 72 in 34 young mongrel dogs, were given root canal filling with Calvital, a calcium hydroxide, after pulp extirpation. Radiological and histopathological investigations were then made of apexification and the healing process. The results were as follows : 1. In radiological investigations, the apex showed continuity of radiopacity on the 35th day after treatment and much denser radiopacity after the 62nd day in the control groups. In the experimental groups, appearances of radiopacity were observed from the 62nd day and these were recognized more clearly on the 180th day. 2. In histopathological findings between the 1st and the 3rd day after treatment, Hertwig's epithelial sheaths and the external layer of the periodontal membrane were necrotic. Calcific clods appeared in the necrotic layers and in the adjacent healthy tissue and showed a positive von Kossa reaction. 3. Between the 7th and the 14th day, part of the necrotic layers dissolved and was resorpted and giant cells appeared. The calcific clods gradually decreased in number and in size. 4. On the 21st day, apical closure by cellular cementum, though irregular because of many and thick accessary roots, was observed in the control groups. In the experimental groups, many giant cells appeared around the necrotic tissue, but the periodontal membrane showed a trend toward recovery. Many young fibers and capillary vessels were observed. 5. On the 35th day, the calcific clods seen to the 21st day disappeared. In the external layer of the periodontal membrane under the residual medication, thick bundles of collagen fibers were seen running vertically toward the root canal. This finding was recognized as the commencement of calcification. Arrangement of the periodontal membrane was irregular in comparison with that in the control groups. 6. On the 62nd day, apexification by cementum-like tissue began and nearly complete apexification was observed in part. Around the hard tissue formed, cementoblast-like cells were seen and collagen fibers penetrating from the periodontal membrane were observed between these cells. 7. On the 180th day, the cementum-like tissues formed became thicker and accessary-root-like tissues were observed in these tissues. However, no complete apexification was observed. 8. No dentin formation was observed in any of the experimental groups, nor was growth of root observed. 9. Hertwig's epithelial sheath became necrotic on the 3rd day and disappeared thereafter. Its relation with apexification and growth of root was not recognized.

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Gingivectomy was performed experimentally in adult rhesus monkeys and patho-histological and neurohistological observations were made of the healing process of the wounds for six weeks from the second day after operation. The results were as follows : 1. Regeneration of the epithelium of the gingivectomy wounds began on the second day after operation and the surface coverage of the wounds was complete on the tenth day. 2. Proliferation of young granulation tissue in the lamina propria of the gingiva began on the third day. Fibration followed and the direction and arrangement of fibers became regular on the 28th day, findings similar to the control's. 3. Bone resorption at the alveloar process was observed in about a half of the cases between the first and fourth week and in two out of six cases in the sixth week. Addition of new bones began on the tenth day and increased thereafter, and the similar findings were observed in four out of six cases in the sixth week. 4. Findings of degeneration such as swelling, lacerations, hypochromatosis, and granular decomposition were observed as early as on the second day around the central cut-surface of the nerve fibers severed in gingivectomy. 5. The degenerative findings around the cut-surface gradually advanced toward the central side and were the most significant on the fifth day. The degeneration of nerve fibers extended to the mucobuccal fold in the alveolar mucous membrane and to the apical region in the periodontal membrane. 6. Regeneration of nerve fibers began in the first week and formation of Bungner's bands was observed in the periodontal membrane from the dental neck to a half of the root and under the attached gingival mucous membrane. 7. Many minute regenerated nerve fibers were seen in the margin of granulation tissue under the new free gingival mucous membrane on the tenth day. Regenrated knob-like nerve endings were seen under the new attached gingival mucous membrane. 8. The findings in the periodontal membrane at the apical region in the second week were about the same as for the control. The amount of distribution however was slightly increased. 9. Many regenerated nerve fibers and free nerve endings were seen under what is called new free gingival mucous membrane of the external marginal epithelium and inner marginal epithelium, and their distribution was about the same as for the control. 10. The nerve fibers under the periodontal membrane and alveolar mucous membrane were still minute in the fourth week and the amount of distribution increased slightly compared with that for the control. The findings in the sixth week were about the same as for the control.

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Transplantation of the superiorly based pharyngeal flap was performed in young beagles, 99 to 110 days old, and pathohistological and neurohistological examinations were made of the healing process of the lesion. The results were as follows : 1. The epithelium at the adhesion site was extremely thin 30 days after operation but reached the normal thickness in about 180 days. 2. Infiltration of the inflammatory cells in the proper layer of the mucous membrane at the adhesion site was hardly observed in 90 days. 3. The diameter of the regenerated nerve fibers after severence increased with time and was nearly normal in 180 days. 4. Schwann cells had a great part in every instance of the regenerated nerve fibers. 5. Most of the regenerated nerve fibers running through the adhesion site regenerated and grew from the pharyngeal flap side. 6. The nerve endings were observed in the regenerated nerve fibers in 30 days. 7. The form of the nerve endings was mostly free nerve endings except that in part of the fibers it was glomerulus in 30 days, and smple ramified nerve endings with arborescence in 90 days, and glomerulus and simple ramified nerve endings with arborescence in 180 days.

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