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The mechanisms by which ionizing radiation ultimately produces a clinical result are very complicated, but a study of the process of polymerization offers a suitable approach. Polymerization can be initiated by very low doses of ionizing radiation. The random events occurring within chemicals, within cells, or within tissues after irradiation are the results of effects produced by the energy exchange at the randomly spaced sensitive areas, and the results can be both degradation and synthesis of polymeric matrices. This concept is proposed as an integrating complement to the chemical and target theories of radiation effects. It should also afford a logical basis for the methodical investigation of the place of chemicals in combination with irradiation in the treatment of tumors.

To the Editor:— I realize that I transposed "small" and "large" in Sentence 2 of the second paragraph to the initial question. It should read: "The organic salt used in intravenous urography is also filtered by the glomerulus in a large percentage but a small part is excreted into the collecting tubules." Dr. Pollack does not appreciate the fact that radiopaques can come through in very dilute form and especially in a very thick patient and not be seen at all. On a radiograph where as on chromocytoscopically a very low percentage of opaque material could be seen with the eye, the usual dye material used is in very low concentration, whereas the organic salts for radiopaque urography are needed in very high concentration. Chromocystoscopy gives no measure of how well a kidney is functioning but whether or not it is functioning.