Abstract
Cumulative mortality rates for embryonated eggs, compiled for a variety of pneumococcal strains, indicated a uniformly high degree of virulence. Based on median lethal dose values for combined infection with influenza C virus and single infection with pneumococcus, it is difficult to conclude that pneumococcal virulence is enhanced in combined infection. However, there was a significant increase in mortality during the first 24 hr following combined infection. A significantly greater in vitro growth rate for pneumococcus was shown in amniotic fluid from virus-infected embryonated eggs. Microscopy study of selected embryos revealed the absence of a discernible inflammatory reaction during the first 24 hr. From 48 through 96 hr after inoculation, inflammatory reactions were restricted to the upper and lower respiratory tract and consisted of a polymorphonuclear leukocyte infiltration in response to the localization of pneumococci in the paranasal sinuses, bronchi, alveolar ducts, and alveolar spaces. Extensive, severe inflammatory reactions were more frequently encountered in the combined infection. The various phases from early exudation to eventual resolution, which characterize pneumococcal pneumonia in the human host, were in clear evidence following both the single and combined infection of the chick embryo.