ON THE NATURE OF THE EMBRYO INHIBITOR IN OVULAR TUMORS OF DATURA.

t The part of this study done at the Childrens Hospital was supported by a grant from Lederle boratories Division, American Cyanamid Company. t R. E. Billingham, L. Brent, and P. B. Medawar, "'Actively Acquired Tolerance' of Foreign Ils," Nature, 172, 603-606, 1953. 2 Throughout this paper, the terms "Rh-negative" and "Rh-positive" refer only to reactions th anti-Rho reagents, and no distinctions are made of further subdivisions within the Rh complex. e use of the term "exposure" is a matter of convenience; we do not, in fact, know the frequency, id, or amount of true serological exposure involved in the maternal-fetal relationship. I W. C. Rogers, A. G. Foord, L. G. Baldwin, and J. P. Kieffer, "The Pasadena Rh Testing boratory, 1947-1950," Western J. Surg., Obstet. Gynecol., 60, 345-352, 1952. 4 P. B. Booth, I. Dunsford, J. Grant, and S. Murray, "Haemolytic Disease in First-born Inlts," Brit. Med. J., ii, 41, 1953. We are indebted to Dr. N. A. Mitchison for calling this prior note to our attention. ;R.' D. Owen, "Immunogenetic Consequences of Vascular Anastomoses between Bovine ,ins," Science, 102, 400-401, 1945; R. D. Owen, H. P. Davis, and R. F. Morgan, "Quintuplet Ives and Erythrocyte Mosaicism," J. Heredity, 37, 290-297, 1946. A. S. Wiener, "Further Observations on Isosensitization to the Rh Factor," Proc. Soc. Exper. 0l. Med., 70, 576-578, 1949.