474 THE TUBERCLE BACILLUS GROUP 
Pathogenesis. //////?a^«.— According to Naegeli/ rather more than 
90 per cent of adults who come to autopsy show scar tissue at the 
apices of the hmgs, which he beheved were healed tubercles. Later 
observations have not fully confirmed these figures, but it appears 
that fully 50 per cent of adults have healed tubercles at this site.' 
Frequently virulent tubercle bacilli have been isolated from the 
center of this scar tissue, but it should be remembered that occasion- 
ally virulent tubercle bacilli have been isolated from bronchial lymph 
nodes which appear to be normal.^ 
Modes of Intection.*— Hereditary TransmissiGn.'^—Tran&im&sion of 
the tubercle bacillus through the sperm has never been established; 
transmission through the ovum is also not definitely established. 
The maternal blood, on the contrary, appears to be a Aehicle through 
which tubercle bacilli may pass, or grow through the placental barrier 
and thus reach and infect the fetus. "^ 
Latency Theory .—Baumgarten'^ believed that tubercle bacilli might 
lie dormant in the body for months or years and become active when 
the "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^ 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 common methods of trans- 
mission of the organism. 
The danger from the dust of rooms, from telephone receivers, from 
drinking cups improperly cleaned, from infected hands and transmis- 
sion by infected flies is as yet not conclusively proven and experiments 
tend to belittle all these possible sources of infection. On the other 
hand, the danger from kissing, and from improperly cleaned utensils 
appears to be borne out by experimental evidence.^ 
Ingestion of milk or meat containing tubercle bacilli must be con- 
sidered as important potential methods of transmission of the organism. 
1 Virchow's Arch., 1900, 160, 426. = Lubarsh: Virchow's Arch., 1913, 213, 417. 
» See Trudeau and Krause (Jour. Med. Res., 1910, 22, 277) for details and literature 
and critical comments. 
'' See Allen Krause (Studies on Tuberculous Infection, Am. Rev. Tuberc, 1919, 
vol. 3; 1920, vol. 4; 1926, vol. 14) for a critical study of this important problem. 
s For an excellent summary of the salient features of modes of infection and their 
bearing upon the parasitism of the tubercle bacillus, see Theobald Smith (Jour. Am. 
Med. Assn., 1917, 68, 669, 764). 
6 See Gartner (Ztschr. f. Hyg., 1893, 13, 126-139) for summary and discussion of 
early literature. Also Schmorl and Geipel: Miinchen. med. Wchnschr., 1904, 51, 1676. 
7 Deutsch. med. Wchnschr., 1882, 8, 305. 
8 Ibid., 1903, 29, 689; 1904, 30, 193. 
9 Brown, Petroff and Pasquera: 1919 Report of the Trudeau Sanitarium and the 
Trudeau Foundation. 
