Spontaneous pneumonia occurred to a considerable extent among stock monkeys at the Army Medical School. This pneumonia occurred chiefly in the form of an epidemic outbreak shortly after the arrival of a large shipment of monkeys, and was shown to be due in large part to transmission of infection from monkey to monkey, either directly or indirectly. That spread of the epidemic was facilitated by overcrowding was indicated by the fact that in a subsequent shipment of monkeys, which were kept in pairs in separate cages and were not allowed to come into contact with the monkeys among which the epidemic occurred, no cases of spontaneous pneumonia developed.
The close analogy between the epidemic of lobar pneumonia that occurred among the monkeys and similar epidemics of lobar pneumonia that occurred during the war among certain groups of newly drafted troops shortly after their arrival at camp is very striking, and would seem to indicate that pneumococcus pneumonia may become an epidemic disease among groups of susceptible individuals when they are assembled under conditions that facilitate the ready transfer of infection from individual to individual.
Bacteriological examination showed the spontaneous pneumonia to be due in the great majority of cases to infection with Pneumococcus Type IV. Immunological classification of the strains of pneurnococci by cross-agglutination tests showed that the majority fell into two biological groups. Two cases were apparently caused by Streptococcus hæmolyticus, two by Streptococcus viridans.
The clinical course of spontaneous pneumococcus pneumonia in monkeys was characterized by sudden onset, high sustained temperature, leucocytosis, rapid respiration with expiratory grunt, cough, physical signs of consolidation, invasion of the blood by pneurnococci, and termination in death or recovery by crisis about the 7th to 9th day. In a few instances the disease was complicated by acute fibrinopurulent pericarditis, by empyema, and by purulent meningitis. It was, therefore, clinically identical with lobar pneumonia experimentally produced in monkeys and with lobar pneumonia in man.
Study of the pathology of spontaneous pneumococcus pneumonia in monkeys showed that it presented the characteristic picture of lobar pneumonia, both macroscopically and microscopically, and was in all respects comparable with the pathology of lobar pneumonia experimentally produced in monkeys and of lobar pneumonia in man.