Another difficulty is one of achieving a proper perspective in dealing with the manner in which the delayed effects which might be produced by radiation would appear. The fact that any delayed effects are by definition ones which do not become apparentat once is baffling to the majority of people, and the fact that they could be produced by something as intangible as radioactive atoms lends the subject a weirdness that is hard to dispel. We have a situation quite the reverse to what has pertained in the past with respect to the great epidemic diseases. Small pox, cholers, and typhoid fever epidemics were very real and terrible events which decimated whole populations in devastating fashion. The problem was to seek the cause and eliminate it by sanitation or by immunizing the population to the specific causative organism. With radiation hazards to society as a whole it is otherwise. There are no formidable pressing measurable effects for which to seek a cause. We can with varying degrees of confidence predict effects from the present rate of radiation exposure to the popu- lation that can never be measured or clearly identified with the specific cause. Yet each projected effect is described in the form of some well-known tragic event, a deformed or weakened child, leukemia, bone cancer, or the vague but seemingly familiar “premature death.” The problem is to find some means of comparing the hazards inherent in fallout and in the medical and industrial uses of atomic energy with some more familiar or man-made hazard which is presently tolerated for one reason or another. There is a natural tendency to reject comparison with the hazards from such a familiar thing as fire. Fire exacts 10,000 lives a year in this country and at the present rate 300,000 per generation. It scars and maims many thousands more. There is the same tendency to reject comparison with the automobile—a very real symbol of modern civilization and the cause each year in the United States alone of some 40,000 deaths and a like number of maimed—atthe present rate more than a million killed per generation, Similarly people reject comparison with the accidental deaths and injuries which are very substantial and a sine quo non for our defense effort. I am sure that you will agree with me that these figures are needlessly high, must and can be reduced, just as injuries from radiation must be kept to a minimum, I suspect one of the reasons for the complacency about our present accident rate is the commonplace nature of the incidents which lead to death and injury. They are recorded in our newspapers daily. A hazard more comparableto that of radiation, smog or air pollution, cannot be used for comparison simply because we have no comparable body of knowledge upon which to base an estimate of the possible deleterious effects on our citizens. For radiation and especially radiation from fallout constitute the only contemporary man-made general environmental hazard about which we have sufficient information to define it at all. Nevertheless, just because it can be defined, there is a greater obligation to keep the radiation hazards minimal. I believe that nuclear energy is here to stay. Like fire, without which man wouldstill be living in caves, it can be a boom to mankind. Likefire, if used carelessly, it will cause death and destruction to property. If used in war, fire can be devastating; more property was de- stroyed and more peopie were killed in the July 10, 1945, fire raid on Tokyo than at either Hiroshima or Nagasaki from atomic bombs. But with megaton nuclear weapons now reality, whether clean or dirty, this would all pale by comparison in the event of a nuclear war. The present rate of exposure from medical and dental x-rays (4 r in 30 years) is of about the same magnitude as the exposure from natural sources of radiation. While the present levels of radiation exposure from weapons testing fallout (0.13 r in 30 years) and future levels at any realistic rate of weapons testing, whether by one nation or by many, are even lower, they are a fraction of the natural radiation exposure. In fact, these levels are well below the levels of radiation which have been employed in experimental work in order to demonstrate detectable pathologic or genetic changes. 2 GENETIC EFFECTS In the field of genetics there are two principal hazards with which we are concerned when we study the effects of ionizing radiation as a mutagenic agent. First, there is the possible risk to the human race as a whole. There is undoubtedly some amount of radiation which, if the entire race were subject to it, would result in a mutation rate which would lead eventually to deg- radation of the species. On the other hand, the maximum tolerable mutation rate for humans, tolerable in the sense of survival of the race, is not known. 278 vewtgg yy 0