It has been mentioned by many clinical observations that the fractures of the mandible caused by dull forces were frequently occured at the mental, angle and condyle regions, and rarely at the regions of the ascending ramus and coronoid process. It is also clinically observed that, though the fractures at the horizontal ramus is usually expressed as that at the alveolar region, the directions of the fracture lines are not always parallel with the axis of the teeth and that most of them run obliquely forward or backward to the axis. The regions and directions of mandibular fractures are examined by the X-ray pictures of 169 mandibular fractures caused by trauma. On the other hand, the strain on the surfaces by the external forces acted upon the dried human mandible hold by the both condyles is measured both quantitatively and qualitatively . The results of them are compared to study the relationship between them.

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It has generally been accepted that dental tartar may be found deposited upon every tooth, but friable, light-colored deposits collect primarily upon the buccal surfaces of the upper molars and the lingual surfaces of the lower incisors, i.e., opposite the exits of the ducts of the salivary glands. On the other respect, increased pH of saliva reduces so much solubility of calcium salts that calcium salt precipitates in saliva. Besides of escape of carbon dioxide from saliva1,2) and proteolysis by some oral bacteria, 3,4) as a factor of local alkalization, Frank 5) mentioned that higher content of free ammonia in saliva was in some relationship with those individuals having a greater tendency to form calculus and claimed that the slight decrease of ammonia content after restless removal of calculus showed that the existence was partially dependent on the ammonia content. The source of ammonia nitrogen in human saliva has been shown to be amino acids and urea.6) Dealing with the ammonia releasing systems in the mouth, Stephan7) reported on the substancial ureolytic action of plaque material and Bliss8) found that tartar scraped from the teeth of normal and nephritic dogs contains urease which acts upon the urea in saliva to produce ammonia. Hine and O’Donnel9i made tests on salivary samples whose 92.8% showed some degree of ammonia production from urea and they suggested a possibility that presence of urease in the mouth would result in an alkaline reaction which might be favor for dental calculus deposition. Ureolytic bacteria were suspected to have some preferential habitation at the particular sites of the mouth where calculus often appear. Topographic difference, therefore, in respect of urease activity of bacterial plaque materials were traced in the present paper.

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During the epidemiological investigations of scrub typhus in Japan, members of the investigative team collected many specimens of sucking lice from three Dsinezumi-Shrews (Crocidura dsinezumi chisai Thomas, 1906) trapped at three different places in Honshu , Japan. The species of louse belongs to the genus Polyplax and seems to be undescribed heretofore. In the present paper , description and drawing of this species will be given.

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When E. coli is kept in an incubator at 37°C, the initial shiny wet ap­ pearance of its surface drys up to come to dull white surface and finally turns to a semi-transparent horny mass. This phenomenon seems to encounter very often, but the clearing is not rather cogent, because the light scattering can always be done on the surfaces of every cell in either case that cells disperse in water or exist as a mass of dried bacterial cells like flour. In the matter of the fact, bacterial spore dried powdery after the same treatment. The first paper of this subjecti; reported that the death rate, by similar dry­ ing of E . coli, was estimated as 325' . but on the contrary, bacterial spore was generally informed to be never affected the life by drying under such physio­ logical temperature. Now it is suspected that the bacterial cell of E. coli might undergo some unknown substancial damage while clearing.

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