SUMMARY OF PATHOGENIC ACTION. 347 



practical purposes an organism having all the microscopical 

 and cultural characters of the diphtheria bacillus, may be 

 accepted as such. Even if it is non-virulent, it is possibly 

 only an attenuated diphtheria bacillus. 



The question, however, has a special interest in regard 

 to the origin and spread of the disease. As is well known, 

 the disease usually spreads by infection, direct or indirect, 

 from patient to patient ; but sometimes it appears to start 

 afresh, as it were. In the latter case the existence of the 

 pseudo-diphtheria bacillus may afford an explanation of the 

 occurrence. This bacillus is frequently found even in 

 healthy subjects. For example, Roux and Yersin found 

 it in the throats of twenty -six out of fifty-nine children 

 examined, living in healthy surroundings. If, accordingly, 

 it may become virulent under certain circumstances, this 

 may explain the occurrence of fresh outbreaks. At present, 

 however, we do not know definitely that such is the case, 

 still less do we know conditions which render it virulent. 



Diphtheria does not affect the lower animals, with the 

 exception of cats, which have sometimes been observed to 

 suffer from a similar disease, in association with human 

 epidemics. Klein has found the diphtheria bacillus in the 

 throat of cats in such circumstances. The so-called diph- 

 theria of pigeons, calves, and other animals is produced by 

 entirely different organisms. 



The term xerosis bacillus has been given to an organism first 

 observed by Kuschbert and Neisser in xerosis of the conjunctiva, and 

 which has been since found in many other affections of the con- 

 junctiva and even in normal conditions. Morphologically it is practi- 

 cally similar to the diphtheria bacillus, and even in cultures presents 

 very minor differences. It is, however, non-virulent to animals, and, 

 according to Eyre, does not produce an acid reaction in neutral 

 bouillon; in this way it can be distinguished from the diphtheria 

 bacillus. 



Action of the Diphtheria Bacillus Summary. From 

 a study of the morbid changes in diphtheria and of the 

 results produced experimentally by the bacillus and its 

 toxines, the following summary may be given of its action in 



