Since the work of Cruz (1) and Rhoads, Castle, Payne, and Lawson (2) iron deficiency has been attributed a pre-eminent role in the causation of the anemia associated with hookworm infection. At one time or another, however, this anemia has been blamed on the effect of hemolytic "toxins" from the hookworm, poor iron absorption, poor protein intake, and blood loss, or a combination of all or several of these factors. An exact evaluation of the role of each of these possible causes is not feasible until quantitative studies are carried out in the human being infected with the human hookworm.In the present study, quantitative evaluation of one of these factors, namely blood loss due to the parasite, is attempted.The radioactive isotope of chromium Cr5' has been used for marking red blood cells (3, 4), estimating their life span and measuring blood volume (4, 5). As a preliminary to our investigation on intestinal blood loss produced by hookworm, we wished to know: 1) How much Cr5' is absorbed from the intestinal tract when it is introduced into the stomach or duodenum of normal or hookworm infected patients, 2) whether Crl' which is absorbed from the intestinal tract enters the circulating erythrocytes in significant quantities, 3) what proportion of Cr5l within the circulating red blood cells appears daily in the feces and urine of non-infected subjects.In quantities. Furthermore, it appears from this study that blood loss, although less than the loss due to A. caninum in the dog (6, 7), is probably an important factor in the genesis of the anemia associated with human hookworm infections2 METHODS All subjects were hospitalized in the Medical or Surgical wards of the Hospital Vargas. Except for patients L.M. and J.F. (Table II), the non-infected subjects were patients who had been hospitalized for surgery, or for local skin conditions. In all subjects in this category, feces were free from hookworm ova in at least three examinations. Patient L.M. was a 30-year-old woman who had had an acute hemorrhage due to placenta previa, and was studied from day 13 to day 25 post partum. Patient J.F. had acute leukemia.Tagging of circulating erythrocytes. Approximately 20 ml. of blood was taken from the antecubital vein and introduced into a sterile bottle containing 3 ml. of A.C.D. solution and approximately 80 microcuries of Cr . The mixture was incubated at 37' C. and gently shaken every five minutes. The blood was then washed three times with 0.9 per cent saline solution in experiments in which intestinal absorption was studied, or reintroduced into the patient's circulation without further washing in the studies of Cr" excretion from circulating erythrocytes.Study of Cr" absorption from the gastrointestinal tract. The washed erythrocytes were resuspended in 5 per cent dextrose. A Levine tube was placed in the patient's duodenum, under fluoroscopic control, and exactly 10 ml. of the suspension was introduced through the tube by gravity with a volumetric pipette, followed by six successive washings with 10 ml. of the dilutin...

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