Nothing need here be said about cancer, the best and most recent evidence tending to show that the disease is not hereditary. The foregoing may briefly suffice to illustrate the general proposition that negative eugenics will seek to define the diseases and defects which are really hereditary, to name those the transmission of which is already certainly known to occur, and to raise the average of the race by interfering as far as may be with the parenthood of persons suffering from these transmissible disorders. Only thus can certain of the gravest evils of society, as, for instance, feeble-mindedness, insanity, and crime due to inherited degeneracy, be suppressed: and if race-culture were absolutely incapable of effecting anything whatever in the way of increasing the fertility of the worthiest classes and individuals, its services in the negative direction here briefly outlined would still be of incalculable value. No other proposal will save so much life, present and to come: and save so much gold in doing so--as one would insist if one were writing a eugenic primer for politicians. To this policy we shall most certainly come: but here, as in other cases, I trust far more in the influence of an educated public opinion than in legislation; though there are certain forms of transmissible disease, interfering in no way with the responsibility of the individual, the transmission of which should be visited with the utmost rigour of the law and regarded as utterly criminal no less than sheer murder. In the next chapter, recognising marriage as the human mode of selection, we must consider it in its relation to eugenics, both positive and negative. CHAPTER XII SELECTION THROUGH MARRIAGE =Historical evidence of control of marriage: Westermarck's evidence.=--To begin with the most recent refutation of the doctrine that marriage selection is uncontrollable, one may quote from the inaugural lecture delivered by Dr. Westermarck in December, 1907, on his appointment as Professor of Sociology in the University of London. He said:--