216 THE AMERICAN MONTHLY [Dec 



sistaace of post-mortem examinations, Sanarelli was able 

 to discover his bacillus in only 58 per cent of the cases 

 of yellow fever. He would be a poor clinician, indeed, 

 who could only diagnose about one-half of the cases. 

 The truth is, however, that during life the microscope 

 could not establish a positive diagnosis. As far as our 

 present methods go, it would be impossible to distinguish 

 between a drop of yellow fever blood and blood from a 

 healthy man. Negative evidence may be presented by 

 the microscope. The presence of the plasmodium malarise, 

 for instance, would prove that a case was suffering from 

 malarial poisoning, and presumably not with yellow 

 fever. But the difl'erential diagnosis between these two 

 diseases is usually easy. The billions remittent fever 

 that in our old text-books of medicine occupied a con- 

 spicuous place in the tables of differential diagnosis with 

 yellow fever, has practically disappeared from the 

 Southern sea border since yellow fever ceased to be an 

 endenic there. It was, in fact, the yellow fever of the 

 natives and of places in the interior. The former were 

 supposed to possess in a certain degree immunity against 

 yellow fever, and the disease was believed to be restricted 

 almost to the littoral. The plasmodium has been found 

 in the blood in cases of yellow fever. The mistake made 

 by the board of experts of New Orleans, when they 

 failed to recognize the existence of yellow fever at Ocean 

 Springs, was due to the finding of the plasmodium in at 

 least two of the cases." 



In February, 1896, Sanarelli discovered and named 

 the Bacillus icteroides having found it in 58 per cent of 

 the cases of yellow fever examined. Why could he not 

 always find it? He states that in laboratory work these 

 bacilli are quickly killed off by the common pus organ- 

 isms, the colon bacillus and others. Having gained en- 

 trance to the circulation through the destruction of the 

 natural barrier by degenerative changes brought by the 



