Mice dying several days after injections of pneumococci, both living and dead, frequently show at autopsy large intrathoracic hemorrhages.
The histological study of the thoracic organs indicates that there occurs in each case a sharply circumscribed, acute degeneration of the wall of some large vessel, usually the ascending aorta or one of the pulmonary arteries. This degenerated portion is torn out by the pressure of the blood with almost complete disappearance of the vessel wall, leading to a gross hemorrhage.
A similar change is occasionally found in the walls of the veins which contain cardiac instead of smooth muscle.
We have found this lesion only in mice which had been recently inoculated with pneumococci. Negative cultures at autopsy, the lack of inflammatory reaction, and the occurrence of the conditions after injection of dead pneumococci suggest the cause to be a toxic degeneration of the vessel wall brought about by the poisons of the injected organisms.