The resistant level of the houseflies to the seven kinds of insecticides, Malathion, Sumithion, Baytex, Diazinon, DDVP, DDT and Chrysron, was examined on the 3 strains collected in Singapore. It was found that most housefly colonies in Singapore showed a higher susceptibility to those insecticides than that of the Takatsuki strain of Japan, especially to DDT. However, the resistant level to Malathion was remarkably higher than that of the Takatsuki strain. The synergists, piperonyl butoxide, Safroxane and S 421, mixed with Malathion were effective for lowering the resistant level of the Malathion-resistant strain.

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Filtration efficiency of high-efficiency particulate air (HEPA) filters is said to be over 99.97% of removal rate against the mist of thermogenerating-type of dioctyl phthalate with average particle diameter of 0.3 μm, as tested by the U.S. Military Standard 282 (1956). Filtration of bacterial aerosols through commercial air filters was tested to examine the efficiency of bacterial filtration with eight kinds of air filters. Percentage of bacterial filtration efficiency (% BFE) of three kinds of HEPA filters showed 100% BFE, while NBS-95 and NBS-85 showed over 99% BFE. BFE of NBS-75 air filter was 91.75%.

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Computed tomography (CT) findings obtained from the first 3,000 scans on 2,031 patients were analyzed and discussions were made on various kinds of neurological diseases, especially from the neurosurgical point of view. CT showed an excellent resolution for three-dimensional morphological pattern of intracranial lesion with a high percentage of diagnostic accuracy as 1eported from other institutes, resulting in making much earlier morphological diagnosis of intracranial lesion possible than any other examination. Scan methods consisted of plain CT, contrast enhanced CT, and metrizamide CT cisternography. Sequential delayed enhanced CT offered more useful information for high diagnostic accuracy, particularly for nature of brain tumor. Metrizamide CT cisternography was performed for the evaluation of cerebrospinal fluid dynamics and diagnosis of skull base tumors. CT is a new, epoch-making and non-invasive diagnostic approach in neuroradiology and contributes to obtain the better achievement of neurosurgical results.

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In order to investigate the effect of burnishing on the marginal closure of non-γ2 amalgam restorations, a single-composition high-copper alloy (Indiloy), a conventional lathe-cut alloy (Lunargent Alloy), and a conventional spherical alloy (Shofu Spherical) were each mixed with mercury and filled in transparent plastic cavities. Half of the specimens were burnished along the cavity margins immediately after packing and again after carving. The remainder was unburnished. A dye was sprayed on their occlusal surfaces after 24 hr and leakage indicated by the dye penetration was observed through the plastic walls, and following facts were found: 1. Burnishing markedly decreased the leakage of all type alloy amalgams. 2. When burnished, the marginal leakage with the high-copper alloy was remarkably less than that with the conventional spherical alloy but slightly more than that with the lathe-cut alloy. 3. The difference in the marginal leakage and in the effect of burnishing among the three amalgams was apparently related to their setting dimensional change curves.

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In order to confirm the ability of physiological recalcification of the human carious dentin, the first layer of carious dentin was removed from the symmetric cavities of bilateral pairs of human teeth, disclosing it by 0.5% basic fuchsin-propylene glycol solution staining. One of the pair teeth was immediately extracted and the other was left in the mouth after filling the cavity with polycarboxylate cement. The Ca content and hardness of the remaining second layer immediately and three months after the operation were compared by an electron probe microanalyzer and microhardness tester. They increased markedly after three months returning to the normal level from inside, proving physiological recalcification. A similar experiment was performed by using bilateral pairs of dog teeth with cavities having artificially decalcified dentin floor. After removing the fuchsin-stainable first layer, one of the pair was immediately extracted and the other was left in the mouth for three months after exposing or filling the cavity with various cements. As the Ca content was compared, a marked recalcification of the second layer of softened dentin was observed after three months returning to the normal level from the inside. The effect of different cavity treatments was slight.

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Neisseria in the early stage of dental plaque was studied. Two hundred seventeen strains of Neisseria were isolated from the 12-hour plaque of 9 subjects by using lactose-agar. The isolated strains were divided into 6 major groups with biological characteristics. One hundred twenty-one strains (56%) produced glycogen-like polysaccharide from sucrose. They were divided into 3 groups. Groups 1 and 2 were identified as N. mucosa and N. sicca, respectively. There were 106 strains of N. sicca, being the most predominant of the species. The number of strains not producing polysaccharide was 96 (44%). Groups 4 and 5 were Branhamella and N. subflava. The absorption spectra of the ethanol extracts of the pigment in each group were similar and this result supported propriety of the classification by biological characteristics. The adhesiveness of Neisseria to the glass plate was examined. Approximately one-half of N. sicca showed an adhesion capacity.

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Distribution of Neisseria, Rothia and streptococci in the early stages of dental plaque was studied on 6 adult subjects. The dental plaque was collected from the surface of the upper incisor at 0, 1, 4 and 12 hours after thoroughly brushing the teeth. Although marked individual differences were observed, Streptococcus was the most predominant and Rothia was also nearly the same as Streptococcus. Neisseria was less in number. The mean distribution of Neisseria was 9.2% (at 0 hour), 11.3% (at 1 hour), 1.8% (at 4 hours) and 3.5% (at 12 hours) and showed a decreasing trend with the passing of time. Streptococci and Rothia showed approximately the same values in all plaque samples. The distribution of the streptococcal species was studied. S. faecalis could not be found in all of the plaque samples. S. milleri and S. salivarius were infrequently found and the latter was considered to be the contamination of saliva. S. mutans was also of the minor group in the early surface plaque. S. milior and S. sanguis were the most predominant species in all stages of the plaque. With regard to the growth rate of the 3 genera, the streptococci were the highest, reaching the stationary phase in 12 hours. Rothia showed a longer lag-phase but the final growth rate was nearly the same as the streptococci. Neisseria showed the slowest growth, the lag phase continuing up to 20 hours. The process of initiation and maturation of the plaque were discussed in relation to the growth rate and adhesion capacity.

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