The Experimental Production of Chronic Empyema in Dogs.

In 1929 we became interested in a new treatment for chronic empyema. The procedure, however, was such a radical departure from the accepted ones that it seemed desirable to test its value on experimental animals, rather than on human beings. Chronic empyema virtually never occurs spontaneously in dogs. We found a paucity of literature on this subject; namely, that chronic empyema in dogs is difficult to produce.

We first opened the pleural cavity and injected into it 2 or 3 cc. of fluid abundantly infected with a variety of organisms. To secure the persistence of this infection a bit of gauze was placed in the cavity before expanding the lungs and closing the wound. These animals all died within 48 hours. At necropsy both pleural cavities were found to be heavily infected. In some there was an accumulation of hemorrhagic, purulent fluid which partially compressed both lungs; in others there was a small amount of thick pus covering all the pleural surfaces. A similar result was obtained when cultures of a single pathogenic organism were used in place of those with several types of organisms. It seemed apparent, then, that a possible explanation of the non-occurrence of chronic empyema in dogs is found in the inability of this species to localize acute pyogenic infections within the pleural cavity. The mediastinum in these animals is a thin, filmy structure, and organisms pass with ease and rapidity from one pleural cavity to the other. The pericardial sac is totally different in this respect; in all of our animals this tissue resisted the penetration of the infecting organisms. Another possible explanation for the failure of empyema to occur spontaneously in dogs lies in the fact that these animals seldom have lobar pneumonia.