120 SCIENCE REMAKING THE WORLD 



bacilli will do little harm. This is true even if they are 

 lodged in a number of places, for a reaction is induced 

 which causes the growth of epithelial and interstitial 

 cells which soon form a globular mass and completely 

 surround the tubercle bacilli. The bacilli may remain 

 alive and virulent but are walled off from the rest of the 

 body. These small pin-head size masses of walled-off 

 bacilli are not always readily detected. They are 

 known as miliary tubercles. 



If, however, the conditions are favourable for the 

 growth of the tubercle bacilli and they find satisfactory 

 conditions for their nourishment within the body, the 

 tissues adjacent to the bacilli are injured and although 

 new cells are formed, these new cells in turn are killed 

 .and the area of dead tissue enlarges, so that we soon 

 have an ulcerating sore in some part of the body. On 

 the other hand, a series of small tubercles may be near 

 together and may combine into one larger tubercle as 

 big as a pea or larger. The tubercle bacilli encased 

 within the wall or cells may not kill the cells which sur- 

 round them, but may gradually cause the degeneration 

 of these cells so that this larger globular tubercle be- 

 comes a soft granular mass. When these conditions 

 develop, a variety of symptoms occur and the individual 

 is then said to have tuberculosis. 



In the vast majority of instances, when infection 

 takes place the number of bacilli is limited and the 

 process of walling them off from the rest of the body 

 does not cause any disturbance. If, however, a con- 

 siderable number of tubercles are being formed at the 

 same time, the growth of the tubercle bacilli and the 



