the lowest activity was found in the muscle. In the same birds the highest levels of activity were in the "gut" or “digestive tract” with the exception of Rigili in which the bone contained the greatest amount of activity. In birds from the southern islands of Igurin, Japtan and Eniwetok the lowest levels of activity were found in the liver. The highest levels for birds of these islands were found in both the skins and bones and were approximately the same. Judging from the data from both birds and rats muscle either takes up or retains a lesser amount of radioactive material than any other tissue or organ sampled. In rats, radioactive materials are deposited in the bone with greater facility than in any other organ or tissue sampled. Evidence that this is not a general uptake by the bone but rather a selective action is indicated by 4 mass absorption curve of one of the six specimens taken at Biijiri (Fig. 14). Inflections in the curve indicate that the beta particles having maximum energies of approximately .2, .8, and 1.3 Mev are pre- sent. A masse absorption curve of a noddy tern bone specimen (Fig. 14) gives some indication of selective deposition in uptake by bone. Well defined inflections which were evident in the rat bone sample are not found; however, the presence of beta particles having maximum energies of approximately .4, -95, and 1.3 Mev are suggested. Conclusions. Food habit as well as range of activityd® - 76 -