TUBERCLE BACILLUS 437 



Latency Theory. Baumgarten 1 believes that tubercle bacilli may 

 lie dormant in the body for months or years and become active when 

 the u resistance" of the body is lowered. The evidence is on the whole 

 opposed to this view, partly because congenital tuberculosis is uncom- 

 mon, chiefly because the organs of fetuses of tuberculous mothers 

 do not cause infection in guinea-pigs. More recently v. Behring 2 has 

 advanced the theory that infection takes place in childhood, probably 

 by ingestion of milk containing tubercle bacilli, and that the manifes- 

 tations of infection become apparent later in life. 



Inoculation Theory. Direct inoculation through the skin is rare. 

 Inhalation Theory. Droplet infection and infection by dust con- 

 taining viable tubercle bacilli appear to be the most common methods 

 of transmission of the organism. 



Ingestion of milk or meat containing tubercle bacilli must be con- 

 sidered as important methods of transmission of the organism. 



Trauma, establishing a locus minoris resistentiae to which tubercle 

 bacilli lying dormant in the body may be transported and set up infec- 

 tion, is probably uncommon. 



Conditions Favoring Infection. Overcrowding with its attendant 

 evils of dark, damp rooms, poor food and general unhygienic condi- 

 tions appears to be a most potent factor in the spread of tuberculosis. 

 No age is exempt, although the disease is somewhat less frequent 

 between the ages of five and ten years, greatest between sixteen and 

 thirty-five years. The sexes are about equally infected. Negroes 

 are especially prone to the disease, possibly because of their surround- 

 ings and manner of living rather than any inherent lack of resistance. 

 Tuberculosis is relatively uncommon among the aboriginal negro 

 races in Africa. Jews appear to be relatively immune to the disease. 

 Those occupations in which dust is generated in large amounts exhibit 

 a higher incidence of the disease than occupations in which dust is 

 not a feature. Catarrhal infections of the respiratory tract appear 

 to predispose to pulmonary tuberculosis as do measles, whooping- 

 cough and influenza. 



Atria of Invasion. The respiratory and digestive tracts (including 

 the tonsils) and the skin are the three portals through which tubercle 

 bacilli enter the tissues of the body. Of these the respiratory tract 

 is more frequently involved. Droplet infection is by far the most 

 common method of transmission of tubercle bacilli; dust-borne infec- 

 tion is probably relatively uncommon. 



1 Deutsch. med. Wchnschr., 1882, No. 22. 



2 Ibid., 1903, 692; 1904, 194. 



