In 1926 G. Ramon and P. Descombey (1) described the phenomenon of flocculation which takes place in mixtures of tetanal toxin and tetanal antitoxic serum. In the same communication Ramon and Descombey reported that with certain sera “abnormal” flocculations may occur. Other workers have also reported, in the case of tetanus, similar “abnormal” flocculations, that is flocculations which occur in zones which do not correspond to true toxin-antitoxin neutralization. In order to overcome the difficulty presented by false zones of flocculation a number of solutions have been proposed. In 1937 Ramon (2) reported that he had prepared a serum which flocculated in a single zone. This was accomplished by rapidly immunizing horses with the filtrate from broth cultures of tetanus which had been incubated for only a few days. Prévot (3) claimed that true and false flocculation could be distinguished by a method based on graphic representation.