Studies on Experimental Pneumonia. Vi. Active Immunity following Expebime.ntal Pneiimococcus Pneumonia in Monkeys. by Russell

The tendency of certain individuals to repeated attacks of pneumonia has at times given rise to doubt whether acquired immunity to pneumonia exists. Considerable evidence, however, can be brought forward to show that a rather high degree of immunity to the pneumococcus follows an attack of pneumonia. The crisis itself is a striking expression of immunity. Furthermore, Dochez 1 has shown that the serum of patients convalescing from pneumonia usually contains protective substances against the homologous type of pneumococcus, and BlakO has demonstrated precipitins in the serum of cases of pneumonia that terminate favorably. Aside from these clinical studies, however, accurate information on the subject of immunity following pneumonia is meager. The experiments herewith reported were performed for the purpose of testing the degree of active immunity in monkeys subsequent to an attack of experimental pneumococcus pneumonia. Usually the monkey has first been subjected to a pneumonia of one of the four pneumococcus types; and following this, the resistance to reinfection with a pneumococcus of the same type has been tested. Then, as in the study of vaccination with livin$ pneumococci (Paper V), tests for cross-immunity against one or more of the other types of pneumococcus have been carried out. The same virulent pneumococci were used in these experiments as in the previous studies and the technique used for producing experimental pneumonia was identical with that already described. Philippine monkeys (Macacus syrichtus) were employed throughout.