More than ever, physicians try to discover the cause of disease. Great discoveries have been made and for a number of diseases certain bacilli have been found to be the specific agents. More than ten years ago it was believed that such a bacillus had been discovered as the direct cause of pneumonia, and many consider pneumonia to-day an infective disease caused by a diplococcus. Still it is a relatively rare occurrence that this bacillus pneumoniæ is found in pneumonia, and the riddle of the nature of this disease is by no means solved.
If I am ready now to bring indirect proofs of the nature of pneumonia before you, without referring to bacillar origin, I am induced to do so from the extraordinary exactness of such proofs. We understand that under the heading of pneumonia a number of different forms of this disease are included and we have reason