Fever and survival in rabbits infected with Pasteurella multocida.

1. Fever and survival rate of New Zealand white rabbits, injected with two doses of live Pasteurella multocida, were compared to determine if the relation between fever and survival observed in reptiles is also seen in a mammal. Since it is known that fever is beneficial in infected reptiles, our experiments were viewed as an initial step in the investigation of a similar potentially beneficial effect in mammals.2. There was a statistically significant correlation between the fever magnitude and survival. As fever increased up to 2.25 degrees C, the survival rate increased. Fevers above this level were associated with a decreased survival rate.3. Antipyretic drugs were administered to half the rabbits. The drugs were ineffective in reducing the fevers produced by injections of large doses of bacteria. Rabbits infused with antipyretics had a decreased mortality rate. The decreased mortality rate may be due to some action of the drugs other than their antipyretic effect.4. In vitro growth of P. multocida at normal (39 degrees C) and febrile (42 degrees C) temperatures was not significantly different. This suggests that the increased survival rate associated with higher fevers was not due to a direct inhibition of the growth of the bacteria by the increased temperature. It may be due to an enhancement of some aspect of the rabbits' immunological defences.5. It remains to be determined whether fever causes a higher survival rate or whether fever is only correlated with survival rate.