102 EFFECTS OF IONIZING RADIATION week. This is in contrast to other mammals where deaths from the acute phase are uncommonafter the 30th day. 6.53 Probability of Survival as Related to Symptoms Hence, individuals exposed in the lethal range (where some, but not all, will die in the first several weeks following exposure) can be divided according to symptomsand signs, into groups having a different prognosis. Thus they maybe divided into three groups in which survival is, respectively, dmprobable, possible, and probable. Tt will be apparent that there is no sharp line of demarcation among the groups. Group 1.—Survival improbable: If vomiting oceurs promptly or within a few hours and continues and is followed in rapid succession by prostration, diarrhea, anorexia, fever, the prognosis is grave; death will almost definitely occur in 100 percent of the individuals within the 1st week. There isno knowntherapy for these people; accordingly, in a catastrophe, attention should be devoted principally to others for whom there is some hope. Group 2.—Survival possible: Vomiting may occur early but will be of relatively short duration followed by a period of well-being. In this period of well-being marked changes are taking place in the hemopoietic tissues. Lymphocytes are profoundly depressed within hours and remain so for months. The neutrophile count is depressed to lowlevels, the degree and time of maximum depression depending uponthe dose. Signs of infection may be seen when the total neutrophile count has reachedvirtually zero (7-9 days). The platelet count may reach very lowlevels after 2 weeks. External evidence of bleeding may occur within 2 or 4 weeks. This group represents the lethal dose range in the classical pharmacologic sense. In the higher exposure groups of this category the latent period lasts from 1 to 3 weeks withlittle clinical evidence of injuries other thanslight fatigue. At the termination of the latent period, the patient may develop purpura, epilation, oral and cutaneous lesions, infections of wounds or burns, diarrhea, and melena. The mortality will be significant. With therapy the survival time can be expected to be prolonged and if sufficient time is provided for bone marrowregeneration the survival rate will be increased. In groups 1 and 2 the blood picture is not as well documented asin group 8. There are good clinical reasons to believe that in the lethal range the granulocyte depressions will be marked and below 1,000 per mm? during the 2d week. Good observations in Japan (21, 22) confirm this contention. However, in the sublethal range it takes much longer for the granulocyte count and platelet count of man to reach minimal values, as compared to other mammals (see Chapter IV and reference 10). Despite the chaotic conditions that existed in Hiroshima, the data of Kikuchi and Wakisaka (22) shows that there was a more rapid and marked decrease in Groups 1 and 2 than in Group 3. Group 3.—Survival probable: This groupconsists of individuals who may or may not have had fleeting nausea and vomiting on the day of exposure. In this group there is no further evidence of effects of the exposure except the hematologic changes that can be detected by serial studies of the blood with particular reference to lymphocytes and_ platelets. The lymphocytes reach lowlevels early, within 48 hours, and may showlittle evidence of recovery for many monthsafter exposure. The granulocytes may show some depression during the second and third week. However, considerable variation is encountered. <A late fall in the granulocytes during the 6th or 7th week may occur and should be watched for. Platelet counts reach the lowest on approximately the 30th day at the time when