86 The Story of the Bacteria 



bacillus. This is shown by the fact that 

 physicians, making autopsies upon the bodies 

 of large numbers of persons who have died 

 from accidents or diseases other than tuber- 

 culosis, have found that nearly every adult 

 has at some time in his life had some small 

 focus of tuberculosis. This his body cells 

 have so successfully and promptly controlled 

 that he has been wholly unaware of the in- 

 fection. But while this shows the resisting 

 capacity of human beings to the tubercle 

 bacillus, it also indicates the wide distribution 

 of the bacillus in the places which man 

 frequents. 



When an individual recovers from tubercu- 

 losis, the bacteria are destroyed and the new 

 growth which is called the tubercle is slowly 

 converted into dense tissue like a scar. Some- 

 times the body cells build a wall of scar 

 tissue around the bacilli and the affected 

 region (Plate VII.), so that the tuberculous 

 process may lie dormant for a long time. 



Now where do tubercle bacilli come from? 

 Remember that they do not grow outside 

 the bodies of warm blooded animals, except 



