It has long been recognized that certain tissue cells can fix toxic substances. Wassermann and Takaki (1) claimed that the brain and cord of normal guinea pigs could fix tetanus toxin. Similar claims have been made by Kempner and Schepilewsky (2) for botulinus toxin, and by Guillain, Laroche and Grigaut (3) for diphtheria toxin. Sachs (4) has shown that arachnolysin prepared from spiders is hemolytic for rabbit cells but that it is not hemolytic for guinea pig cells, and furthermore, corresponding with this specificity, the hemolysin of arachnolysin is absorbed by the stroma of rabbit erythrocytes, but not by the stroma of guinea pig erythrocytes. Similar observations were made by Jacoby (5) with crotin, prepared from the seeds of Croton tiglium, which is hemolytic for rabbit cells, but not for those of the guinea pig or dog. That calf erythrocytes have a selective action for the neurotoxic and hemolytic property of cobra venom has been claimed by Bang and Overton (6).