The mechanical properties of the walls of blood vessels have an important influence on the flow of blood and passage of pulse waves along them. Though a certain amount of information is available concerning the mechanical properties of the aorta and its main branches (Burton, 1954), we have been unable to find any observations on the pulmonary circulation. Hence, in view of the increasing interest in human pulmonary hmmodynamics, it seemed worth while to investigate the physical characteristics of the wall of the pulmonary trunk in man. SUBJECTS AND METHODSObservations were made at necropsy on 48 patients in whom there was no cardiac or pulmonary disease. A circumferential strip, 1 cm. in width, was cut from the pulmonary trunk 1 cm. above the level of the pulmonary valve by means of a rectangular punch operated by means of a simple lever. The loose adventitial connective tissue was stripped off and each end of the strip placed in a serrated clamp (A in Fig. 1), tightened by means of a screw. One clamp was fixed to a metallic rod; this was attached to a cross bar (B) which could be moved by means of a screw (C) and two parallel runners (Dj upwards and downwards in a bath filled with physiological saline and maintained at 370 C. The other clamp was suspended vertically above the first by means of a nylon thread attached to one arm of a balance. The opposite arm of the balance acted as a pointer along a circular scale which indicated directly the weight that had been applied to the strip of artery. The scale was calibrated by the application of a series of standard weights for a particular adjustment of the counterweights E and F. Thus, by turning the screw, the strip of artery was subjected to an increasing extensile load, the magnitude of which could be read off on the scale of the balance.The length of the strip at any load was measured by a telescopic optical system which moved along a vertical scale. A hair-line within the optical system was aligned first with the clamp at one end of the strip of artery and then with the other. The distance between the two clamps could thus be measured along the vertical scale which could be read to 0 0I cm. by means of a micrometer adjustment and a Vernier scale. The length of the arterial strip was measured first in the unstretched state and then with extensile loads of 10, 20, 40, 60, and 100 g. weight, successively. Five minutes were allowed between the application of an increment in load and the measurement of the degree of extension. During this time a certain amount of slow elongation of the strip occurred while the load was maintained constant by adjusting screw C. In 30 specimens the extensile load was reduced to zero immediately after the final measurement at 100 g. weight. After a further 5 minutes, the length of the strip was again measured, and it was found to average 3 0 per cent greater than the original length. The original length of the strip between the clamps varied between 2-06 and 4 18 cm., the average being 3-29 cm. In view of the variation in initial len...

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We investigated the possible cariostatic effect of strontium in the absence of effective amounts of fluoride by relating the DMFT index of the population to the strontium and fluoride concentrations in drinking water and enamel surfaces. The epidemiological survey was conducted in two neighboring districts in the northwest part of Greece, involving 582 children ranging in age from 11 to 14. The average DMFT values were 5.26 in the high-strontium (2.9-7 ppm Sr) area and 6.95 in the low-strontium (0.2-1.3 ppm Sr) area, while fluoride was low (less than 0.06 ppm) in both districts. Further, the average strontium concentration in surface enamel was higher in the high-strontium area.

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The aim of this study was to compare dental caries and oral hygiene status in children aged 6–12 years in the Athens area between 1982 and 1991. Dental examinations were carried out by the same examiners in 773 children attending the same randomly selected schools sited in areas of different socioeconomic levels. The findings concerning the deciduous dention showed that the percentage of caries-free children increased in 1991 compared to 1982 by 38%. The mean deft scores were reduced by an amount ranging from 21 to 34%. Changes in caries prevalence were also observed in the permanent dention. The percentage of caries-free children for the total examined population increased by 94% while the reduction in DMFT index ranged between 38 and 70%. Treatment need was significantly lower in 1991 compared to 1982 in both dentitions. Debris index scores were similar while oral hygiene habits had slightly improved by 1991. The decline in caries levels may be attributed to the increased use of various forms of fluoride. Furthermore, dental health awareness of the population has improved.