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By means of the fat-pad transplant technique, competing systems of mammary-gland elements were established in the gland-free (cleared) and intact fat pads of C3H female mice. These experiments demonstrated the presence of a growth-regulating system within the intact mammary gland which determines both the spacing of the parenchymal elements and the extent of mammary-gland growth. This growth-regulating system was shown to be effective between normal gland elements, between normal gland elements and hyperactive outgrowth, between hyperactive outgrowths, and, to a limited extent, between normal ductal elements and tumors. The ability to override this growth-regulating system appears to be the principal characteristic of neoplastic tissue.
Faulkin et al. (Fri,) studied this question.