Arsenic has been used extensively for hundreds of years in the treatment of many diseases. During the past one hundred and fifty years it has been employed most commonly in the form of solution of potassium arsenite, U. S. P. (Fowler's solution). One of its chief uses, prior to a few years ago, was to combat anemia. There appears to be no doubt that prior to the discovery by Minot and Murphy1 of the effectiveness of liver in pernicious anemia, solution of potassium arsenite properly given was responsible for many remissions produced in this disease.2 Hence, arsenic gained the reputation of being an antianemic drug and was employed, frequently with a measure of success, in the treatment of certain types of anemia. On the basis of these facts, it would seem to be paradoxical that any favorable effect could be elicited by its administration to patients suffering from