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 
