Genetic polymorphism has been demonstrated in man for many characteristics including blood groups, serum proteins, tissue enzymes, and hemoglobins. A class of chromosomal polymorphism involving constitutive heterochromatin has now been found. Through the use of a special technique that permits visualization of heterochromatin, seven heterochromatin variants have been found among four individuals. These results suggest a very high frequency of variability of heterochromatin in the population.

A correlation between specific fragile sites and cancer breakpoints has been suggested raising the question of fragile site expression as a predisposing factor in the occurrence of cancer in some persons. Before addressing the question of increased fragility among patients at high risk for cancer, we analyzed the variability of aphidicolin-induced fragile sites among nine normal persons and also among repeated samples from three of these individuals. Considerable variation in both the frequency and location of these fragile sites was observed and the data strongly suggest the significant variation of 6 of the 16 selected sites to be primarily due to sampling differences. These findings indicate that the use of fragile sites as a screening tool for patients at high risk of cancer should be carefully monitored relative to the variation inherent in both culture and individual expression.

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Women who work in operating rooms have an increased risk of spontaneous abortion and there appears to be a correlation in the incidence of miscarriage and operating room exposure during the first trimester of pregnancy (Euromed 1972, Cohen, Bellville and Brown 1971, .American Society of Anesthesiologists 1974). It is well known that spontaneous abortions in the general population represent a fetal wastage (Potter and Adair 1963). The Geneva Conference