Experiments are reported which show that the virulent Bordet-Gengou bacillus can produce a significant lymphocytosis and an interstitial mononuclear pneumonia in both the monkey and the rabbit. Both of these reactions occur apparently as the result of a toxic material formed in vivo from the Bordet-Gengou bacillus and are not dependent on the multiplication of the organism itself.
It was also shown that the strictly avirulent form could also cause an interstitial mononuclear pneumonia but no lymphocytosis. This interstitial mononuclear pneumonia was thought to be the result of the foreign substance produced by the organism when it was in this stage. This was substantiated by the fact that this lesion could be produced both by living and dead organisms.