In Experiment 12 B. influenzæ was injected into the trachea and two days later identified in a culture made from the pharynx; four days after inoculation Pneumococcus IV was injected into the trachea. The animal was killed seven days after the first inoculation, and three days after inoculation with pneumococcus. The lower half of the upper lobe of the right lung and the greater part of the lower and middle lobes were consolidated. The pleural surface of the consolidated areas was dull red and covered by a small amount of fibrin. The lower lobe, with the exception of a small part at the summit, was very firmly consolidated, on section pinkish gray in the anterior part and deep red in a small zone at the posterior border. The cut section was conspicuously granular. The trachea and bronchi contained mucus. Cultures from the trachea, the right lung and the right pleural cavity contained Pneumococcus IV in pure culture. Alveoli in the consolidated part of the lung were filled with polynuclear leucocytes and fibrin.

Lobar pneumonia has been produced by the introduction of Pneumococcus IV into the trachea. It is doubtful if preceding inoculation of B. influenzæ has influenced the course of the disease.

The foregoing experiments have shown that B. influenzæ introduced into the nasopharynx or into the trachea of monkeys is capable of causing lesions of the mucosa of these structures; the microorganism persists within the nasopharynx or trachea and is recoverable during a variable period of from two to eleven days after inoculation. Spontaneous infection of monkeys with B. influenzæ has not been observed. The animals infected with the microorganism are ill during several days, but the experimental disease like most instances of human influenza is self limited. Following inoculation of the nose and throat of monkeys with B. influenzæ there is discharge from the nose, tendency to epistaxis and absence of leucocytosis.

Bronchitis was produced by the introduction of B. influenzæ into the trachea of monkeys, and the microorganism was recovered from the nasopharynx two and three days following inoculation. There was no leucocytosis. In two experiments death occurred following inoculation, and in both instances it was found that the animal suffered with tuberculosis which had produced only trivial lesions of the lungs. In both animals staphylococci were obtained from the internal organs. There was bronchitis with changes in the bronchi which, although not characteristic, resembled those found in association with B. influenzæ in man. It is noteworthy that B. influenzæ is usually found mixed with other bacteria in the bronchi of those who have died with bronchitis and pneumonia following influenza. In the experimental animals there was in places superficial loss of ciliated epithelium, exudation of polynuclear leucocytes, infiltration of the subepithelial tissue with plasma cells and hemorrhage into this tissue.

In one instance simultaneous injection of B. influenzæ and S. hemolyticus, freshly obtained from autopsy upon a man dying with pneumonia following influenza, caused bronchitis and bronchopneumonia; there were acute lymphangitis and infiltration of the interstitial tissue of the lung with polynuclear leucocytes such as occurs in human cases, but the lesion had not proceeded to suppuration.

In man B. influenzæ is usually found in greatest abundance upon the mucosa of the respiratory passages, less frequently it invades the alveoli of the lungs and is almost invariably found in association with other microorganisms. In company with other microorganisms B. influenzæ penetrates into tissues outside the lungs. In Experiment 7 it has entered the pericardium, with streptococcus, and in Experiment 9 with pneumococcus. When B. influenzæ and streptococcus are injected into the peritoneal cavity of a mouse both organisms appear in the blood, whereas in the absence of streptococcus, B. influenzæ seldom leaves the peritoneal cavity.

Typical lobar pneumonia has been produced for the first time in monkeys by injecting pneumococci (in quantity as small as 0.33 c.c. of suspension) into the trachea. With the animals available it has not been possible to adjust the dosage of the two microorganisms so that the influence of one upon the other might be determined. Pneumococcus III, in small quantity, introduced into the trachea has produced typical acute lobar pneumonia in the stage of gray hepatization. A similar lesion has been produced with Pneumococcus IV obtained from the lung of a man dead with pneumonia.

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