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 considered. 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 infec- 

 tions, particularly tuberculosis and syphilis, are perhaps 

 the most wide-spread 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 organ- 

 ism 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 lodgement at some point 

 of low resistance. It may penetrate to the true lung 

 tissue with the air current, but it probably settles in 



