Fortunately, our practical knowledge is by no means as deficient as these statements would suggest. Radioactivity, and processes similar to radioactivity, surround us and have surrounded our ancestors for as long as life has existed on earth. We do not know what life is, and we do not know in what detailed manner life is affected by radioactivity; but we have broadly based and certain knowledge that artificial radioactivity will produce similar effects to those produced by the natural background of radioactivity. This background, therefore, provides us with a yardstick to which all man-made contaminations can be compared. There is a final obstacle to the explanation of matters connected with radioactivity. This is the secrecy which has been associated with the development of nuclear energy, and in particular with the military applications of nuclear energy. The arguments for keeping information concerning weapons secret are strong, proper, and generally understood. There is, however, no such strong argument, and in fact no possibility for secrecy connected with the widely dispersed radioactivity which originates from the weapons. In recognition of this fact, secrecy has been completely and properly removed from this field. It is not surprising that it took some time to do so. Administrative decisions have been involved, and these are never taken in a very great hurry. Even though world-wide radioactive contamination has been since 1955 open to general scientific discussion, the time does not seem to have been sufficient to insure a wide dissemination and explanation of the results. There may also remain some lingering doubts whether all relevant information has been made available. In actual fact, the scientific information on this important topic is completely and freely available at the present time. Information concerning the peaceful applications of nuclear energy is also completely and freely available. Even in the field of military applications, much of the essential information has been published.