The Collaborative International Dictionary of English v.0.48:

Pyrogen \Pyr"o*gen\, n. [See Pyrogenous.]
   1. Electricity. [R.]
      [1913 Webster]

   2. (Physiol. Chem.) A poison separable from decomposed meat
      infusions, and supposed to be formed from albuminous
      matter through the agency of bacteria.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pyrogen
    n 1: any substance characterized by its great flammability
    2: any substance that can cause a rise in body temperature [syn:
       pyrogen, pyrectic]