"METABOLISM OF IRON"

To the Editor:—  In an editorial in The Journal, July 27, various claims were made for a method of following iron metabolism, making use of radioactive iron. The editorial writer appears to have overlooked a communication published in the November 1939 issue of Physical Review (Barnett, Abraham: The Use of Radioactive Forms of the Common Elements in Physiology, Physical Rev.56:963, 1939) casting serious doubts on the validity of conclusions drawn as to the behavior of nonradioactive metals from experiments carried out in which radioactive forms of the same elements are used. Briefly, taking the red cell as an example, it was pointed out that, since it is known that its limiting membrane is composed of an electrically charged polar lipoidal substance having a thickness estimated to be of the order of one molecule, the bombardment of the cell wall at close range by electically charged particles emanating from