The Distribution of Radioactive Iodine in Rats

operation. The remaining two rats were unoperated controls. In the second experiment, 96 rats were grouped, 3 days after arrival, so that each cage contained rats of sizes ranging from the smallest to the largest found in the entire lot. Half of the rats in each cage were then implanted with the tumor as before, and the other half were sham-operated to serve as controls for the rats in the adjacent cage with which they were paired. Injection of iodide.—Each of the 148 rats received only a single injection. This consisted of 0.8 ml. per 100 grams of body weight of the radioactive sodium iodide solutions described below. It was given sub cutaneously in the dorsal flank. After injection each rat was kept separately. In the first experiment, on 52 rats, injections were begun 7 days after tumor implanta tion and were carried out over a period of a week (Table I). In the second experiment, on 96 rats, injections were made at 5, 6, 11, 12, 15,and 16 days aftertumor implantation. On the sixteenth day, the injection was divided between the dorsal flanks of each rat to avoid external leakage from the needle puncture which may