278 BACTERIOLOGY. 



products. The tubercle bacilli may cause the diffuse 

 growth of a tissue identical in structure with that of 

 miliary tubercles that is, composed of a basement 

 substance containing epithelioid, giant, and lymphoid 

 cells. This diffuse tubercle-tissue also tends to undergo 

 cheesy degeneration. 



Distribution of Tubercle Bacilli in the Tissues. In 

 acute tuberculosis, especially when caseation is rapidly 

 spreading, the bacilli are usually abundant. They are 

 generally scattered irregularly through the tissues or 

 in small groups. They are occasionally found in the 

 leucocytes and in the giant and epithelioid cells. In 

 subacute and chronic lesions they are usually few in 

 number. Sometimes in old caseous materials numerous 

 stained granular points are seen ; these are supposed 

 by some to be a resting stage similar to spores. 



Infection. Infection by the tubercle bacillus takes 

 place usually through the respiratory tract or the diges- 

 tive tract, more rarely through wounds of the skin. 



In the majority of cases the mode of infection is 

 evident. Pulmonary tuberculosis as a primary dis- 

 ease, and not occurring in young children, may be con- 

 sidered to be caused chiefly by the direct transmission 

 of tubercle bacilli through kissing, soiled hands, hand- 

 kerchiefs, etc., or by the inhalation of tuberculous dust. 

 Intestinal and mesenteric tuberculosis, which is rare 

 among adults and common with children, is probably 

 due not only to swallowing the bacilli received in the 

 above ways, but also to the ingestion of tuberculous 

 milk. Lupus is probably always produced by the 

 inoculation of tubercle bacilli on the skin or mucous 

 membranes, which is indicated by the fact that the 

 original seat of the disease is so often on a wounded 



