ABSENCE OF FEVER IN PLANARIAN - TURBELLARIA - PHOGOCATA-GRACILIS

1. Groups of 5 to 10 planarians (Turbellaria: Phogocata gracilis) were placed in a water gradient of temperature extending from 0 to 40-degrees-C over 0.8 m. In control sessions, the planarians avoided water at less than 9-degrees-C and more than 23-degrees-C. 2. In the 4 hr following intracoelomic injection of E. coli endotoxin (2.5, 5 and 10 ng/mg), human interleukin-2 (0.5 and 2 mU/mg), interferon-alpha (0.02, 0.2, and 1 U/mg), and vehicle the thermopreferendum was not different from control. 3. The pyrogenic drugs were toxic at higher concentrations, therefore active. 4. The diffusion of injected substances to the whole body was verified with a dye. 5. These negative results are not in favor of fever in Platyhelminthes. The absence of fever in both Platyhelminthes and Molluscs, while Arthropods and Annelids can have fever, might be explained by a common phylogenetic origin of the former.