The essential points of our results are as follows: The saprophytic Bacillus megatherium produced a definite pulmonary lesion which in gross appearance resembled the lesion of lobar pneumonia. The lesion was one of intense leucocytic exudation which, as in some other cases of experimental lobar pneumonia, did not invade the framework of the lung. But the exudate contained no fibrin. There were practically no bacilli, either in the heart's blood or in the lung. The growth of two colonies from one of the cases hardly changes the rule. The lesion did not progress after twenty-four hours; nor did it show a definite increase in extent or intensity with the increase in quantity of the injected cultures. The resolution of the exudate began practically at the end of twenty-four hours and was far advanced on the third day. Although there was considerable leucocytic infiltration there was no phagocytosis apparent twenty-four hours after inoculation.

Taking all the facts into consideration one gains the impression that the lesion produced by the saprophytic Bacillus megatherium differs only quantitatively from that produced by an avirulent pneumococcus. The fact stands out prominently that a saprophytic bacterium is capable of producing a pneumonic lesion similar in gross appearance to that of mild lobar pneumonia. It is not improbable that other saprophytes may be capable of producing pneumonic lesions which, in specific instances, may resemble lobular pneumonia.

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