SUMMAKY 367 



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 transformation 

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

 The general opinion is that the two organisms are distinct species 

 which are 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 is, however, non- virulent to animals, and does not pro- 

 duce an acid reaction in sugar-containing bouillon, or does so to only 

 a slight extent ; in this way it can be distinguished from the diphtheria 

 bacillus. Its morphological characters are shown in Fig. 123. 



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 - *jf 



toxins, the following sum- ffi^' 



mary may be given of its 

 action in the body. Locally, v** 1 it 



the bacillus produces in- ^\ 



flammatory change with 

 fibrinous exudation, but j> *~ 



at the same time cellular * >* <fr 



necrosis is also an out- 'j 

 standing feature. Though ^ 4, 

 false membranes have not ijfj 

 been produced by the 

 toxins, a necrotic action 

 may result when these are -*- 



injected subcutaneously. Fm> 123 ._Xerosis bacillus from a young 

 The toxins also act upon agar culture, x 1000. 



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 walls of 

 arterioles and capillaries so often met with in diphtheria is 

 another example of the action of the toxin. The toxins have 



