Melanocytic nevi of diameter greater than or equal to 2 mm were counted on most of the skin surface of 349 adolescents aged 14-15 years of European race or ethnicity in Dunedin, New Zealand. Total counts are described by means of a form of Poisson-error log-linear modeling suitable for data showing unexplained variation (NE Breslow, Appl Statist 1984;33:38-44). There were marked interpersonal variation in the number of nevi; only some was attributable to observed factors. The mean and median counts were 23.8 and 18 nevi, respectively. The estimated ratio of the number of nevi for females compared with males was 0.7 (95% confidence interval (CI) 0.6-0.8). Greater amounts of sunbathing were associated with greater numbers of nevi. Hair and eye color, socioeconomic status, and sunburn history did not show statistically significant effects. Time since menarche and shaving status also showed no effects. Lack of suntan was associated with lower counts. Freckling was positively correlated with higher counts; the severe freckling group had an estimated ratio of 1.9 (95% CI 1.3-2.8) compared with those with no or very few freckles. The results are consistent with the hypothesis that ultraviolet radiation exposure from recreational sun exposure positively influences the total burden of nevi in normal subjects. Comparison with other epidemiologic studies suggests that the typical ultraviolet radiation dose-nevus yield curve might be steeper in males than females. Unexplained variation of nevus count may reflect heterogeneity of constitutional factors not yet measured in epidemiologic studies.

SUMMARY1. Changes in the water and ion contents of rabbit renal cortical slices, which had been bathed, immediately after slicing, in air-equilibrated media at room temperature ('freshly prepared slices'), were followed during subsequent incubation at 25 TC in oxygenated media of the same composition as the initial bathing medium.2. In comparison with conventional 'equilibrated' slices (slices incubated at 25 TC in oxygenated ordinary medium immediately after slicing) these 'freshly prepared' slices had increased tissue water, sodium and chloride contents and low tissue potassium contents.3. Control freshly prepared slices incubated at 25 TC in oxygenated ordinary medium recoveredwithin 4min to the tissue water content that is usual forrabbitrenal cortical slices incubated in oxygenated ordinary medium at 25 'C. Freshly prepared slices incubated at 25 'C in oxygenated media containing 1 mM-ouabain took 75 min or more to recover to this usual tissue water content. Thus the presence of 1 mmouabain in both bathing and incubation media produced a marked inhibition of the volume recovery observed when freshly prepared slices are incubated in oxygenated media at 25 'C.4. Reduction of the ouabain concentration reduced the inhibition of cell volume recovery.5. Replacement of medium glucose by 3-0-methylglucose did not inhibit cell volume recovery in the absence of ouabain.6. The oxygen consumptions of slices that were bathed and incubated in 1 mMouabain media were similar to those of slices initially bathed and incubated in ouabain-free media and then incubated in ouabain media. Thus the effect of ouabain in inhibiting cell volume recovery was unlikely to be secondary to inhibition of cellular energy production.7. The tissue potassium content of slices incubated aerobically in 1 or 10 mM ouabain fell to an apparently stable value of approximately 100 m-mole/kg dry wt., which corresponds to a calculated concentration ratio of 10: 1 across the cellular membrane, suggesting that some residual potassium uptake may still have been occurring.8. These results indicate that in freshly prepared rabbit renal cortical slices ouabainsensitive mechanisms play a major role in cell volume recovery. They are not in accord with the postulate that renal cortical cells possess a separate ouabaininsensitive mechanism regulating cell volume.

The age-standardized mortality rates for malignant melanoma of the skin in immigrants to New Zealand were compared with those of New Zealand-born non-Maoris. Immigrants from European countries had mortality rates that were generally similar to those prevailing in their countries of origin, although, among immigrants from the British Isles, early age at migration was associated with a mortality rate similar to that of New Zealand-born non-Maoris. In a community survey, British immigrants were not less likely to have had severe sunburn, but had fewer moles, than New Zealand-born non-Maoris. The lower melanoma mortality, and the effect of age at migration, could be mediated by differences in mole frequency.

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