The nuclear DNA content of normal human endocrine and exocrine pancreatic cells was determined by Feulgen microdensitometry. Exocrine cell nuclei consistently yielded only diploid DNA values, while islet cell nuclei showed distinct diploid, tetraploid and octaploid classes. The existence of a strict positive correlation between nuclear size and DNA content in individual nuclei permitted the assignment of islet cell nuclei to one of three polyploid classes after staining by Gomori's modification of the Mallory-Heidenhain azan technic. It was thus determined that polyploidy is confined entirely to beta cells, while alpha and delta cells remain diploid. Although a complete analysis was made on only six adult specimens, the unequivocal volume-DNA relationship established permits the assumption, based on the observation of numerous other human pancreases, that the phenomenon is a generalized one.

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