OBSERVATIONS CONCERNING THE ETIOLOGY OF PRIMARY ATYPICAL PNEUMONIA

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Abstract
Young guinea pigs inoculated intranasally with sputum, throat washings, blood, lung and spleen from cases of primary atypical pneumonia have been found to develop a non-fatal pneumonitis with an incubation period of about 2 weeks. Animals inoculated with similar materials from other sources, and with lung suspensions from normal guinea pigs, do not show pulmonary lesions. The responsible agent will pass through a Berkefeld V filter and is apparently not bacterial in nature; attempts to propagate it in tissue cultures and developing hens'' eggs have been unsuccessful. Neutralization tests with acute and convalescent sera from patients, as well as with sera from recovered animals and from immunized rabbits, have given inconducive results. A pneumonitis may also be produced in cotton rats with the guinea pig agent. In these animals neutralization tests have likewise been unsuccessful. However, recovered guinea pigs and cotton rats are both immune to reinoculation of the homologous and heterologous animal strains, and partial or complete immunity against these passage strains can be produced in normal animals by the repeated intranasal inoculation of sputum and throat washings from patients with primary atypical pneumonia.