In the latter part of the nineteenth century arsenic, chiefly in the form of solution of potassium arsenite (Fowler's solution), was the standard remedy in diseases of the blood. It was used to increase the red blood cells and hemoglobin in certain anemias and to decrease the white blood cells in leukemia. Cutler and Bradford1were among the first to study quantitatively and scientifically the effects of arsenic on the cells of the blood. In 1878 they published the results obtained in five cases studied at the Boston City Hospital; two of the cases showed a normal blood, two were cases of anemia, and one was a case of leukemia. They made careful total counts of the white and red blood cells and found that the administration of solution of potassium arsenite in health caused a progressive decrease in the number of red and white blood corpuscles. In simple