1. Pneumonia has been consistently produced in normal monkeys by intratracheal injection of Streptococcus hæmolyticus.

2. The pneumonia produced has been shown to be comparable with hemolytic streptococcus pneumonia in man with respect to its clinical features, complications, and pathology.

3. Two pathologic types of the disease have occurred, interstitial pneumonia and confluent lobular pneumonia. Both types have been found in the same animal.

4. The type of pneumonia has appeared to be dependent upon the amount of streptococcus culture injected, interstitial pneumonia following the injection of small amounts and being an expression of considerable resistance, confluent lobular pneumonia following the injection of large amounts and being an expression of comparative lack of resistance.

5. Study of the distribution of streptococci in the lungs and of the character of the lesions in early stages of the disease has shown that streptococci may primarily invade the pulmonary tissue by penetration of the walls of the larger bronchial branches and that they are distributed from the points of invasion by way of the peribronchial, perivascular, and septal interstitial tissue and lymphatics. Infection of the alveoli is likewise primarily an interstitial invasion of the alveolar walls by streptococci.

6. In one experiment it was found that preliminary injury to the respiratory tract by gassing with chlorine and that lowering of resistance by a preceding intraperitoneal injection of Bacillus influenza without local injury to the respiratory tract greatly facilitated invasion of the lungs by Streptococcus hæmolyticus.

7. A normal monkey inoculated in the nose and throat with Streptococcus hæmolyticus failed to develop pneumonia and showed no evidence of infection of the upper respiratory tract.

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