PATHOLOGIC ANATOMY OF TUBERCLE BACILLUS. 191 



six hours ; by a 5 per cent, solution in about one hour. The 

 germ in the sputum is active for a long time, and infection 

 may occur after two or three months. 



Pathogenesis : The tubercle bacillus is the exciting cause of 

 tuberculosis in man as well as in animals. It is a matter 

 under discussion whether the organisms which cause tuber- 

 culosis in fish, birds, and cattle, are distinct species from 

 Bacillus tuberculosis of man ; or whether they are aberrant 

 types of the same ; or a modification of this germ due to 

 changed surroundings a question of adapting itself to its 

 environment. It is a rather remarkable and at the same 

 time significant fact that animals which in their native state 

 are immune to tuberculosis, succumb very rapidly to the 

 infection as soon as they are kept in captivity. The monkey 

 is an excellent illustration of this. Nearly all captive 

 monkeys die from tuberculosis, whereas the wild monkey is 

 immune to the disease. 



Guinea-pigs are naturally very susceptible to tuberculosis, 

 and are used extensively for experimental and diagnostic pur- 

 poses. An injection of a very small amount of tubercular 

 material into a guinea-pig will cause death in about three or 

 four weeks. Autopsy reveals extensive tubercular lesions in 

 which the tubercle bacillus is always found. Tuberculosis in 

 animals can be produced by feeding them with tubercular 

 sputum or other material containing the bacillus ; by causing 

 them to inhale a very fine vapor spray in which the bacilli 

 are suspended ; and by inoculation into any part of their 

 bodies. 



Of the domestic animals, cattle and pigs are the most sus- 

 ceptible. Cold-blooded animals are naturally immune unless 

 the bacillus has first been accustomed to grow at very low 

 temperatures. Birds, with but few exceptions, are immune 

 to tuberculosis. 



Pathologic anatomy of the tubercle bacillus : The tubercle is 

 the constant anatomic product of the tubercle bacillus. It is 

 seen in all the organs and tissues. Lodgement of the bacillus 

 in any tissue is followed by the production of many new cells, 

 which comprise both regular, fixed, or connective-tissue cells, 

 and modifications of the same i. e., the so-called epithelioid 



