therefore necessary to wash and remove the radioactivity from the boat, clothes and the human body. For reference, the radioautograrhs of the letters written by the oil which was on the deck of the Koei Maru and the gloves of the crew are shown in Figure 5. ii. About the Tuna. Since different people have different interests in this subject, it involves many intricate problems. I will simply refer to the medical aspect of this problem. The question is then how much of the radioactive ash can be eaten together with the tuna without violating the safety of the human body. This is again not a simple problem. First of all, the ash itself consists of various elements and they are absorbed in the human body at various rates. Even the same element will be absorbed differently according to the form of compounds they constitute. ‘Furthermre, they deposit in various organs such as the bone, kidney, liver and thyroid. Different elements have different half-lives both physical and biological. To simplify the argument, we shall assume for the moment that the ash consists of only the most dangerous element Sr70, In the usual form of compounds, about 60% of Sr90 is absorbed by the body through digestive organs and about 0% deposits in the bones. Its physical half- life is abous 20 years, while the biological and effective half-lives are 3.9 x 10” days (about 10 years) and 2.7 x 102 days (about 7. years), respectively. It is therefore very difficnlt to discharge once it deposits in the bones. The permissible dose of deposit in the body is 1 micro- curie. Since 0% of the absorbed strontium deposits in the bones, it is dangerous to eat more than 2.5 microcuries, It is not unambiguous how mch count the radioactivity of 2.5 microcuries will give to the G.M. counter at 10 cm, since it depends on the geometry, measuring instrument, the thickness of the mica window of the G.M. counter, etc. But, roughly speaking, it may be about 5000 ct/min. Since the safety limit adopted today is 100 ct/min at the distance 10 cm, it may be concluded that it is not dangerous at all to eat the tuna though the above calculation is based on several assumptions. What measure should be taken when the radioactive substance entered the body or one is exposed to the external radiation to such an extent that certain injury is expected? The first thing to do is to have the blood-counting several times. If any anomaly is found, one has to be checked carefully. Next, the radioactivity in the urine shonld be> maesured. We shall not discuss it in details here. iii. Radioactive rain, etc. Fall of ash, rain and snow with the radioactivity have been observed at several places in Japan. The detail is not available yet. But it may not be dangerous to the human body and others as far as the intensity of natural and artificial radioactivities remains to be of the present order of magnitude. S. Conclusion. (omitted) Z