The evolution of an acute inflammatory exudate produced in rabbits by the intraperitoneal injection of saline has been described. Evidence has been presented that polymorphonuclear leucocytes release endogenous pyrogen into the cell-free fluid of the exudate. Leucocytes from such exudates have also been shown to release pyrogen into the surrounding medium during incubation in vitro at 37°C. The results of parallel cytological studies have provided evidence which suggests that the leucocytes give up their pyrogen while functionally intact.
These observations add further support to the hypothesis that polymorphonuclear leucocytes play a significant role in the pathogenesis of fever.