In 1940 Smith1 of the Fearing Research Laboratory, Brookline, Mass., demonstrated that the normal human menstrual discharge is highly toxic for rats and rabbits. Subsequent studies2 have shown that its toxicity varies in direct proportion to the amount of endometrial débris. From this Smith concludes that the toxin is probably a specific autolytic product of the endometrial cells. The toxin is apparently a euglobulin. This euglobulin is highly antigenic for rabbits, giving rise to an antitoxic serum that will protect rats from multilethal doses of menstrual discharge.
While this work was in progress, Menkin3 of Harvard Medical School reported the presence of a similar toxic euglobulin in canine inflammatory exudate. For this toxin he proposed the name "necrosin." He found subsequently that necrosin could be fractionated by differential solubility methods. One of the fractions is a nontoxic pyrogenic factor, for which he proposed the name "pyrexin." He