Nonvisualization of Kidney-Reply

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.