One other pertinent fact is that these rapidly dividing hematopoietic cells are extremely sensitive to radiation. (Hematopoietic cells are those that are actively forming blood cells and are therefore those that should be attacked selectively.) The dose required is of course many times that needed for diagnostic studies, and careful observation of the results is necessary to determine that exactly the desired effect has been obtained. There exists some controversy over this course of treatment. No one denies that the lives of patients have been lengthened notably. Nevertheless since the purpose of the procedure is to reduce red cell formation, there exists the hazard of too great a reduction, and the possibility of causing leukemia (a disease of too few red cells). There may be a small increase in the number of cases of leukemia among those treated with ³²P compared with the general population. The controversy arises over whether the ³²P treatment _caused_ the leukemia, or whether it merely prolonged the lives of the patients until leukemia appeared as it would have in these persons even without treatment. This is probably quibbling, and many doctors believe that the slight unproven risk is worth taking to produce the admitted lengthy freedom from symptoms. Gold-198 The last ailment we shall discuss in this section is the accumulation of large quantities of excess fluid in the chest and abdominal cavities from their linings, as a consequence of the growth of certain types of malignant tumors. Frequent surgical drainage was at one time the only very useful treatment, and of course this was both uncomfortable and dangerous. The use of radioactive colloidal suspensions, primarily colloidal gold-198, has been quite successful in palliative treatment: It does not cure, but it does give marked relief. [Illustration: Showing:] Colloidal gold in shield Saline solution To peritoneal or pleural cavity Radioactive colloids (a colloid is a suspension of one very finely divided substance in some other medium) can be introduced into the abdominal cavity, where they may remain suspended or settle out upon the lining. In either case, since they are not dissolved, they do not pass through the membranes or cell walls but remain within the cavity. Through its destructive and retarding effect on the cancer cells the radiation inhibits the oozing of fluids. Gold-198 offers several advantages in such cases. It has a short half-life (2.7 days); it is chemically inert and therefore nontoxic; and it emits beta and gamma radiation that is almost entirely absorbed by the tissues in its immediate neighborhood. The results have been very encouraging. There is admittedly no evidence of any cures, or even lengthening of life, but there has been marked reduction of discomfort and control of the oozing in over two-thirds of the cases treated. Beads, Needles, and Applicators