The mammary gland constitutes a peculiarly suitable field for clinical and pathologic investigation of the cancer process not only because of the vast surgical pathologic material it affords, but more especially because of the opportunity to study the physiology of the gland in its relation to tumor formation. It is my special purpose to present the available evidence on the relation between "chronic mastitis," cysts and papillomas to cancer of the breast.
The morphologic appearances of breasts at birth, puberty, lactation and pregnancy possess important bearings on the conception of certain pathologic states. Studies of breasts at birth show that the development of the breast is not always complete at the end of nine months of fetal life and that the appearances of breasts vary enormously in different male and female infants. Hyperplasia of the epithelium and of the pericanalicular and periacinous connective tissue and lymphocytic infiltration are