Abstract

THE agent isolated in cotton rats, hamsters or embryonated hen's eggs by Eaton et al.1 2 3 from patients with cold-agglutinin-positive atypical pneumonia has been the subject of considerable controversy. This agent could be propagated in embryonated eggs and produced pneumonic lesions in hamsters and cotton rats after intranasal inoculation. The results of neutralization tests in hamsters or cotton rats that suggested the development of antibody to this agent during convalescence from atypical pneumonia have not been accepted by certain workers since the challenge inoculum did not produce pneumonitis in all inoculated animals. In addition, the question of latent agents in cotton . . .