CHAPTER X. 

 THE MORE CHRONIC INFECTIOUS DISEASES. 



THE diseases which have been discussed are the most 

 important acute infectious diseases, and now those which are 

 accustomed to follow a more prolonged course must be con- 

 sidered. It should be emphasized, however, that any one of 

 these may assume a rapid or fulminating character and run 

 its course quite as rapidly as the acute infections. These 

 chronic infections, particularly tuberculosis and syphilis, are 

 perhaps the most widespread of diseases. 



BACTERIUM TUBERCULOSIS. 



Tuberculosis is an infectious disease capable of attacking 

 any organ or structure in the body, although its commonest 

 site is the lung. The organism is the Bacterium tuberculosis 

 or tubercle bacillus. The organism enters the body chiefly 

 through the mouth and nose, usually by the air, but also in 

 food and drink. If it follow the air passages it may settle 

 upon the nasal, buccal, pharyngeal, laryngeal, or bronchial 

 mucous membranes. These it penetrates, and settles usually 

 where there is lymph tissue. This it follows with the lymph 

 flow, and finds lodgment at some point of low resistance. 

 It may penetrate to the true lung tissue with the air current, 

 but it probably settles in some of the smaller air tubes, and 

 extends into adjoining lung tissue by continuity. It may 

 enter the lungs by following the lymph way, or it may get 

 there from the blood stream or lymph when it has been taken 

 into the intestines in food or drink. These bacteria can pass 

 through a mucous membrane into the deeper tissue without 

 (134) 



