APRIL 1957
GRAFTED TISSUE--"We discovered that the power to react against homografts could be prevented from developing if we injected an animal at a very early age with cells from the donor strain--most conveniently cells of the spleen. In adult mice the injection of such cells ?increases the mouse's resistance to a graft from the donor. But if the spleen cells are injected in a mouse in the fetal stage or very shortly after its birth, the opposite happens: the mouse becomes tolerant of grafts from the strain that provided the spleen cells, though it remains intolerant of homografts from mice of other strains. --P. B. Medawar" [Editors' note: Medawar shared the 1960 Nobel Prize in Physiology or Medicine for his work on acquired immunological tolerance.]

END OF PARITY--"There were two mesons, called tau and theta. Tau, in the course of time, disintegrated into three pi mesons; theta, into two pi mesons. What was baffling was that in every property except the mode of decay, tau and theta were identical twins. Could they be one and the same particle? Decay of a particle by two different modes was certainly permitted by theory and precedent, but in this case the principle of conservation of parity stood in the way. Tsung Dao Lee of Columbia University and Chen Ning Yang of the Institute for Advanced Study boldly faced up to an embarrassing but insistent possibility: perhaps the parity-conservation law simply broke down in the realm of particle decays like tau's and theta's! --Philip Morrison" [Editors' note: Lee and Yang won the 1957 Nobel Prize in Physics for this work.]