Upon concentration, hemolyzed red cells and stroma-free supernatant were found to be inhibitory to the K-9 strain of Entamoeba histolytica. Dialysis of the concentrated supernatant revealed that the toxicity probably resided in a non-diffusible, high molecular weight substance. Hemoglobin was found to be highly inhibitory to the K-9, 103, and 200 strains at levels of 8 mg/ml; and it is likely that this substance accounts for the toxicity of RBC. Hemin in solution was found to be highly toxic to these three strains at levels of 75 µg/ml of culture. It is suggested that the heme moiety is responsible for the toxicity of both hemoglobin and whole RBC to the ameba. Low concentrations of hemoglobin and hemin showed a stimulatory effect on the multiplication of E. histolytica. Hematoporphyrin HCl showed only stimulatory effects. All evidence indicates that the effects of hemoglobin, hemin and hematoporphyrin on strains K-9, 103 and 200 are identical. This would seem to suggest that the resistance of strains 103 and 200 to the effects of whole RBC as noted in another publication was the result of the ability of these strains to cause lysis of the erythrocytes. Such lysis results in considerable dilution of the soluble materials of the RBC.
Present address: The Lutheran General Hospital, 1775 Dempster Street, Park Ridge, Illinois.