416 DIPHTHERIA 



suffering from diphtheria. Boycott's statistics show that the 

 time of its maximum seasonal prevalence precedes that of the 

 diphtheria bacillus. To what extent, if any, it is responsible 

 for pathological changes in the throat, must be considered a 

 question which is not yet settled. Hewlett and Knight have 

 found evidence that a true diphtheria bacillus may assume the 

 characters of Hofmann's bacillus, but attempts to effect the trans- 

 formation . have met with negative results in the hands of other 

 observers. The general opinion is that the two organisms are dis- 

 tinct species with comparatively easily distinguished characters. 



Xerosis Bacillus. — This term 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 conjunctiva 

 and also in normal conditions. Morphologically it is practically similar 

 to the diphtheria bacillus, and even in cultures presents very minor 

 differences ; it, however, grows more slowly on serum, and its colonies 

 have a tougher consistence and a more irregular margin. It is non- 

 virulent to animals, and does not produce an acid reaction in glucose 

 bouillon, or does so to only a slight extent ; in this way it can be dis- 

 tinguished from the diphtheria bacillus. It is still doubtful whether it 

 is pathogenic to the human subject. Its morphological characters are 

 shown in Fig. 118. 



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 

 toxins, the following sum- 

 mary may be given of its 

 action in the body. 

 Locally, the bacillus pro- 

 duces inflammatory change 

 with fibrinous exudation,, 

 but at the same time 

 cellular necrosis is also 

 an outstanding feature. 

 Though false membranes 

 have not been produced 

 jfjh y/ by the toxins, a necrotic 



^4" l^ action may result when 



Fig. 118.— Xerosis bacillus from a young tnese are injected sub- 

 agar culture, x 1000. cutaneously. The toxins 



also act upon the blood 

 vessels, and hence oedema and tendency to haemorrhage are 

 produced; this action on the vessels is also exemplified by 

 the general congestion of organs. The hyaline change in the 



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