external radiation rise from a value of about 100 mr/year at sea level to something like 230 mr/year at 5000 to 6000 ft altitude in the United States. These numbers are considerably larger than those expected on the basis of earlier calculations and measurements,’’?":?8 the increase apparently being due to the cosmic rays and their increase with altitudes.”® In addition, the ef- fects of radioactivity in the soil and in building materials made of stone or soil are considerable, amounting in some instances to 50 or 100 per cent of the average natural background dose at sea level, and the magnitude of the medical exposures to X-rays approximates on the average those due to all natural sources.” We see, therefore, that whatever the extent of our ignorance of the biological effects of radiation, we do know that these effects are not unexperienced by the human species, even from the genetic point of view, since it is clear now that persons living at high altitudes on granitic rocks always have received extra radiation many times greater than is contained in the radioactive fallout from the testing of nuclear weapons, and that even those iiving on certain sedimentary rocks at sea level always have received about 10 to 20 times the present fallout dose. Of course, this does not mean that any of the effects from radioactive fallout are in any way negligible and it does not mean that certain numbers of people will not be injured by radioactive fallout radiations, even though these numbers be very small relative to the total population of the world. However, the problem is bounded, and common sense and good judgment can be brought to bear on the extent of the biological hazards even though they are not now known exactly, and probably will not be well understood for many years. Researches to increase this understanding are being done, especially in the United States and United Kingdom and other countries. Information on radioactive fallout and all of its aspects, both physical and biological, is collected and collated by the United Nations’ Scientific Committee on the Effects of Atomic Radiation, which is drafting its first report at the present time. 6. From our study of radioactive fallout from testing, we have learned much of value about the circulation of the atmosphere of the world, and we have much more to learn as the study continues, particularly in the stratosphere by balloon and aircraft sampling techniques being carried out principally in the United States at the present time. As we undertake the problem of locating the fallout in the oceans, we undoubtedly will learn much of interest to oceanographers about the circulation of the water in the seas. 7. From our understanding of radioactive fallout from tests, we are the better able to devise methods of civilian defense against fallout in the case of nuclear war, and widespread 2opular interest in the potential possible hazards from radioactive fallout from nuclear tests has led to a considerable understanding on the part of the general public of these strange phenomena. From this debate and study may come the protection for millions in case nuclear war should occur. Understanding of the nature of the mechanism by which radioactive fallout is disseminated has led to the reduction of the offsite fallout from testing. We know now that bombs placed upon the ground produce relatively more local fallout and therefore less world-wide fallout. It seems likely that firing on the surface of the sea has a similar, though probably considerably less marked effect. 2 RECENT DATA AND THEIR IMPLICATIONS Figure 1 of this paper and additional Figs. 1, 2, 9, 10 and Tables 1 and 44 of Part 1 and Table 50 of Part 2 of this volume are up-to-date versions of earlier publications. The most recent results are given for the fallout observed for rainfall collections, for the Sr®° content of milk (fresh and dry), for human bone, and for animal bone. It is particularly interesting to note that the data continue to show the principal features noted previously and thatlittle new in principle has appeared. The tables mentioned above show the data for the HASL pot program, Lamont bone program, and the HASL pasture program. The figures appearing in Volume1, referred to above, present data on HASL pots, Pittsburgh rainfall, New York City milk, and HASL powdered milk. Figure 2 shows preliminary data on the stratospheric content of Sr®°. The data are preliminary for the reason that the air filter efficiencies are unknown at the present, although estimated to be something like 25 per cent. The samples are taken by pumping stratospheric air through filters which are then analyzed. It is clear that, even though an enormous scatter 257