Pathogenesis 323 



remained latent during fetal life, for Birch-Hirschfeld has 

 shown that fragments of a fetus, itself showing no tubercular 

 lesions, but coming from a tuberculous woman, caused fatal 

 tuberculosis in guinea-pigs into which they were inoculated. 



The most frequent channel of infection is the respiratory 

 tract, into which the finely pulverized pulmonary discharges 

 of consumptives and the dusts of infected rooms and streets 

 enter. Fltigge, Laschtschenko, Heyman-Sticher, and Be- 

 ninde * found that the greatest danger of infection was 

 from the atomized secretions, discharged during cough, from 

 the tuberculous respiratory apparatus. Nearly every one 

 discharges finely pulverized secretions during coughing and 

 sneezing, as can easily be determined by holding a mirror 

 before the face at the time. Even though discharged by 

 consumptives, these atoms of moisture are not infectious, 

 except when tubercle bacilli are present in the sputum. 

 Experiment showed that they usually do not pass further 

 than 0.5 meter from the patient, though occasionally they 

 may be driven 1.5 meters. A knowledge of these facts 

 teaches us that visits to consumptives should not be pro- 

 longed; that no one should remain continually in their 

 presence, nor habitually sit within two meters of them ; 

 also that patients should always hold a handkerchief before 

 the face while coughing. The rooms occupied by con- 

 sumptives should also be frequently washed with a dis- 

 infecting solution. 



Probably all of us at some time in our lives inhale living 

 virulent tubercle, bacilli, yet not all suffer from tubercu- 

 losis. Personal variations in predisposition seem to account 

 in part for this, as it has been shown that without the 

 formation of tubercles virulent bacilli may sometimes be 

 present for considerable lengths of time in the bronchial 

 lymphatic glands the dumping-ground of the pulmonary 

 phagocytes. 



In order that infection shall occur, it does not seem 

 necessary that the least abrasion or laceration shall exist 

 in the mucous lining of the respiratory tract. 



Infection also commonly takes place through the gastro- 

 intestinal tract from infected food. At present an over- 

 whelming weight of evidence points to the presence of 

 tubercle bacilli in the milk of cattle affected with tubercu- 



193. 



* " Zeitschrift fur Hygiene," etc., Bd. xxx, pp. 107, 125, 139, 163, 



