A hundred roentgens all at once, or several times this amount over a protracted time period, will not cause sickness or death that can be directly blamed on the radiation. However, such a dose of radiation may have harmful biological consequences which are more subtle. An exposed individual may develop an increased susceptibility to certain diseases, notably bone cancer and leukemia. Leukemia is a fatal disease in which the white blood cells multiply too rapidly. A person who receives a hundred roentgens does not necessarily contract bone cancer or leukemia. Rather, his chance of contracting these diseases during his lifetime may have been increased. Knowledge of this kind can be obtained only with the help of statistics. If, for example, a large number of mice receive a heavy dosage of radiation over a long period of time, one finds that the incidence of tumors and leukemia is higher amongst such irradiated animals than the natural incidence of these diseases. Direct evidence with human beings—fortunately—is rather scarce. Statistics exist on the survivors of Hiroshima and Nagasaki, and also on radiologists. The latter group probably receive several hundred roentgens during their professional lifetimes. In addition, some statistics exist on children who have been treated with large doses of radiation for enlarged thymuses. Persons suffering from ankylosing spondylitis, which is a painful disease of the spinal joints, have also been treated with large X-ray doses. The statistics in all these cases lead to the same conclusion: that large doses of radiation increase the likelihood that an individual’s life will be shortened by leukemia and possibly also other cancers. Furthermore, it appears (mainly from the experiments on animals) that the increased likelihood is simply proportional to the amount of radiation received, at least for doses in the neighborhood of several hundred roentgens or so. This of course sounds frightening. But the radiation doses from the world-wide fallout are in a completely different class from those we have been discussing. They are very much smaller. On the average human bones are getting about 0.002 roentgens per year from the Sr⁹⁰ in the fallout. In addition the whole body is receiving a roughly equal amount in gamma rays, mainly from Cs¹³⁷. These figures apply to new bone in young children who have grown up in an environment of Sr⁹⁰ in the northern part of the United States. This is a region of maximum fallout. Adults whose bones were made for the most part before the atomic testing started are getting about 0.0003 roentgens per year from Sr⁹⁰. None of these figures appears to be alarming.