The relationship of the fever caused in rabbits by bacterial pyrogens to the fever produced by the injection of the sterile exudates of acute inflammation was investigated by recording the responses of normal and pyrogen-tolerant animals to injections of exudate. Exudates were produced by the intrapleural injection of turpentine in dogs.

The duration of the febrile response in rabbits after a single dose of exudate was found to be much shorter than the fever following an injection of bacterial pyrogen.

Animals given daily injections of exudate demonstrated no tolerance to its fever-promoting effect.

Animals tolerant to bacterial pyrogens showed no diminution in responsiveness to exudates.

Daily injections of exudate failed to establish tolerance to bacterial pyrogens in rabbits.

It is concluded that the fever-promoting property of sterile exudates is not due to the presence of bacterial pyrogen.

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