On the basis of earlier findings, which suggested that interlobar spread in experimental canine pneumonia was due to the flow of infected edematous exudate from the initially involved lobe to other parts of the lung by way of the air passages, an attempt was made to induce secondary lesions by means of the intrabronchial and intratracheal injection of fluid pneumonic exudate. Such exudate was aspirated from the lungs of dogs with rapidly evolving lesions and injected through a bronchoscope into other animals showing well localized monolobar involvement which is seldom associated with spread to other parts of the lung. The deposition of relatively small amounts of fluid exudate in the larger air passages 24 to 48 hours after the onset of the disease was followed regularly by the occurrence of secondary lesions provided the dog was maintained in a position favoring the flow of fluid into the depths of the lung. Lesions in the various lobes could be produced at will by arranging the position of the animals so that the injected fluid would be carried by gravity into the most dependent bronchial opening nearest the point at which the exudate was deposited. Pneumonia was produced by this means as readily in normal dogs as in those with infection already present. If, however, the dog was placed in a position unfavorable to the flow of fluid into the bronchi, infection did not occur. Likewise the injection of viscid pneumonic exudate, with the animal tilted at an angle most favorable for entrance into the lobe bronchi, did not result in pulmonary involvement. These artificially induced secondary lesions resembled in every way both macroscopically and microscopically those occurring spontaneously in the course of the experimental disease.

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