Abstract
Pregnancy did not affect the average weight or the relative size of the lobes of the hypophysis. A differential count of the 3 types of cells indicated no significant difference between the controls and experimental Series I. Series II, 45 days older than Series I, showed a slight significant increase in chromophobes, and a decrease in acidophils and basophils. No definite type of "pregnancy cell" was found. Slight changes in cell counts occurred at different stages of the estrous cycle.