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The Influence of Blockage of the Nipples on the Occurrence of Hyperplastic Nodules in the Mammary Glands of C3H Mice^*

( Roscos B. Jackson Memorial Laboratory, Bar Harbor, Maine)

The mammary glands of 62 virgin females of the C3H/Fe strain possessing the milk agent and an equal number of C3Hb/Fe females lacking the milk agent were blocked on one side by cutting their nipples at weaning age. The animals were killed at 7–9 months of age. The numbers of hyperplastic nodules found on the blocked and unblocked sides were compared.

In the C3H/Fe mice possessing the milk agent more hyperplastic nodules were found in the mammary glands of the blocked sides (92) than on the unblocked sides (57). This difference is statistically significant (P = 0.001).

In the C3Hb/Fe mice lacking the milk agent hyperplastic nodules were not found in the mammary glands of either on the blocked or unblocked sides.

^* This investigation was aided in part by a grant-in-aid from the American Cancer Society upon recommendation of the Committee on Growth of the National Research Council and in part by a research grant from the National Cancer Institute of the National Institutes of Health, Public Health Service.

Received 11/23/51.