Production of Pneumonia in Rats by Intravenous Injection of Pneumococci. ∗

Abstract

Rake 1 demonstrated that pneumonia could be produced in mice when the pneumococci were introduced by the intravenous route. The important factors were the strain and dose of the organism, and the breed of mice. Twelve of 87 mice had macroscopic lesions; 6 of the 87 failed to show any microscopic lesions. The pathology of the various stages encountered was clearly described.

Prior to this work, with a few exceptions, intravenous injection of pneumococci has failed to give rise to pneumonia. Although it has long been postulated that the origin of the infection might be by way of the blood stream, there has been little evidence to support it.

Employing the Schwartzman phenomenon, Witebsky, Neter, and Ward 2 were able to localize pneumococci injected intravenously in dermal lesions of rabbits.

In our experiments, rats were inoculated intrabronchially with 0.1 cc of sterile mucin according to a technic previously described; 3 immediately thereafter, the animals were injected intravenously (using the tail vein) with various amounts of culture. The data are presented in Table I.

In interpreting these results it must be remembered that these animals received only one inoculation of organisms, many of which were distributed throughout the body and removed by the fixed phagocytic cells. It is noteworthy that in at least one rat, the disease was produced with as small an inoculum as 10^-7 cc of culture.

Although in the past it has been generally impossible to produce pneumonia in experimental animals by intravenous injection of pneumococci, this may be accomplished in rats following intrabron-chial inoculation of sterile mucin. The presence of mucus material in the lung or some comparable condition is a necessary predisposing factor for the localization of the pneumococci.