ACTION OF BACTERIA 287 



accompanied by exudation, and simulate the early stages of abscess 

 formation ; the latter is the specific effect, and results, as in leprosy 

 and tubercle, in infective nodules. The site in some diseases, like 

 typhoid (intestinal ulceration, splenic and mesenteric change) or 

 diphtheria (membrane in the throat), may be definite and always the 

 same. But, on the other hand, the site may depend upon the point 

 of entrance, as in tetanus. The distant effects of the toxin are due 

 to absorption, but what controls its action it is impossible to say. 

 We only know that we do find pathological conditions in certain 

 organs at a distance from the site of disease, and without the 

 presence of bacteria. We have a parallel in the action of drugs ; 

 for example, a drug may be given by the mouth, and yet produce a 

 rash in some distant part of the body. In the second place, (ii.) 

 toxins produce toxic symptoms. Fever and many of the nervous 

 conditions resulting from bacterial action must thus be classified. 

 We have, it is true, the physical signs of the pathological tissue 

 change, for example, the large spleen of anthrax or the obstruction 

 from diphtheritic membrane. But, in addition to these, we have 

 general symptoms, as fever, in which after death no tissue change 

 can be found. 



We may now consider briefly some of the more important forms 

 of disease produced by bacteria.* 



Diphtheria 



Diphtheria is an infective disease characterised by a variety 

 of clinical symptoms, including a severe inflammation usually 

 followed by a fibrinous infiltration (constituting a membrane) of 

 certain parts. The membrane ultimately breaks down. The parts 

 affected are the mucous membrane of the fauces, larynx, pharynx, 

 trachea, and sometimes wounds, or the inner wall of the stomach. 

 Diphtheritic conjunctivitis may also occur. The common sign 

 of the disease is the membrane in the throat; but muscle 



* Bacterial diseases may be classified as follows : 



(1) Diseases common to man and certain animals, and presumably trans- 



missible from animals to man, and vice versa, e.g. bubonic plague and 

 tuberculosis. 



(2) Diseases common to man and animals, but not known to be directly 



transmissible, e.g. actinomycosis, tetanus. Diphtheria, belongs to this 

 class, or Group (1) or (5). 



(3) Diseases transmitted from animals to man, but not as a rule communicated 



from man to man owing to interfering conditions, e.g. anthrax, glanders, 

 rabies, vaccinia, foot-and-mouth disease, meat-poisoning, psittacosis, 

 and possibly infections due to pus bacteria. 



(4) Certain specific symbiotic relations requiring two hosts for the complete 



cycle of life of the micro-organisms, e.g. malaria, trichinosis, tape-worm 

 infection. 



(5) Diseases occurring in man, but not, as far as known, in animals, e.g. 



typhoid fever, gonorrhoea, leprosy. 



