PATHOGENIC BACTERIA. 29I 



bacilli into animals produced lesions having the histological 

 characters of tubercles, but caseation did not take place. 



The small tubercles first fprmed are called gray or mili- 

 ary tubercles. As they become larger they also frequently 

 become confluent. The larger, confluent, caseous tubercles 

 are often called yellow tubercles. Swollen tuberculous lymph- 

 nodes of the neck are among the manifestations of the con- 

 dition formerly known as scrofula. 



Masses of caseous tubercles sometimes undergo soften- 

 ing. In the lungs the discharge of the softened material 

 results in the formation of a cavity. This formation of a 

 cavity in the lungs is frequently, if not usually, accompanied 

 by secondary infection with pyogenic micrococci. Caseous 

 tuberculous masses may become partly calcified. Very often 

 they may be encapsulated by new formed fibrous or scar tissue. 

 It is possible for tuberculosis to become cured for all practical 

 purposes by means of this process. Autopsies on human 

 subjects have shown that such cures not rarely take place, 

 especially in tuberculosis of the lungs occurring over a localized 

 area. The statistics of autopsies vary widely as to the number 

 of persons that at some time of life suffer from tuberculosis 

 (25 or 30 per cent, and upward). When a tuberculous area 

 has become caseous and encapsulated and apparently quies- 

 cent, it is possible for it to be excited to renewed activity under 

 suitable conditions, and, owing to the softening and the dis- 

 charge of infected material into one of the vessels or cavities 

 of the body, a wide-spreading and rapidly fatal tuberculosis 

 may follow. 



Tuberculosis may become disseminated throughout the 

 body from a small focus as a starting-point. The tubercle 

 bacilU may travel through the lymph-spaces and affect adja- 

 cent tissues, some of them reaching the nearest group of lymph- 

 nodes. In tuberculosis of the lungs it is usual also to find 

 tubercles in the bronchial lymph-nodes, and in tuberculosis 



