2Q2 MANUAL OF BACTERIOLOGY. 



a dry, yellowish-white, friable mass, resembling dry cream- 

 cheese. Such material is said to be caseous, and the pro- 

 cess is called cascation. Prudden and Hodenpyl found that 

 the injection of dead tubercle bacilli into animals produced 

 lesions having the histological characters of tubercles, but 

 caseation did not take place. 



The small tubercles first formed 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 condition 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, accom- 

 panied 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 

 upwards). When a tuberculous area has become caseous 

 and encapsulated and apparently quiescent, it is possible for 

 it to be excited to renewed activity under suitable conditions, 

 and, owing to the softening and the discharge 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 



