Infection by Inhalation. 525 



fection with tuberculosis resulted after inhalation of 0.01 mg. 

 while infectiou through the alimentary tract required 10 mg. 

 of tubercle bacilli culture. 



In view of these results we can no longer doubt the possi- 

 bility of inhalation tuberculosis. As to the practical importance 

 of this mode of infection, we must remember that comparatively 

 few bacilli reach the terminal ramifications of the bronchial 

 tubes through the medium of ordinary infected air and also 

 that the body is provided with natural means to protect itself 

 against even considerable quantities of virus. Another fact 

 that should receive due consideration in this connection is that 

 it is only with difficulty that calves are infected by means of 

 intratracheal injections, even of large masses (10 cc. bacillus 

 emulsion) of virus. 



The question as to whether an infectious inhalation produces pul- 

 monary tuberculosis primarily by aerogenous infection, or secondarily 

 by lympho-hematogenous infection is yet an open one. While some 

 authors believe that the inhaled bacilli give rise to the development of 

 the first tubercles in the nucous membrane and its lymph follicles (Zieg- 

 ler, Ponfik, Schmorl, etc.), others (e. g., Orth, Ribbert and Baumgarten) 

 believe that the bacilli are immediately absorbed by the mucous mem- 

 branes and deposited in the bronchial glands from where they reach 

 the lung tissue and the walls of the bronchial tubes through the lymph 

 and blood circulation. The tubercles and cheesy foci which here de- 

 velop are then supposed to give rise to a tuberculous bronchitis and 

 broncho-pneumonia. 



This view is especially applicable to pulmonary tuberculosis of 

 domestic animals. According to Bongert the first tuberculous changes 

 in the lungs of cattle are observed in the posterior lobes to which places 

 tubercle bacilli would be most apt to be carried first. This is due to the 

 fact that the pulmonary artery passes in a straight direction from its 

 point of entrance toward the base of the lung, while the artery for the 

 anterior lobe branches off at an angle in a more or less opposite direction. 

 In a direct infection from the inhaled air the anterior lobes would natur- 

 ally become infected first because the origin of the bronchial branch 

 supplying this lobe as well as that of the first, branch of the main bron- 

 chus, according to Baerner, is situated at the lowest point of the main 

 bronchus. *Consequently material inhaled with the air, especially fluids, 

 is drawn principally into the anterior lobes of the lungs. Pigs often 

 aspirate food particles into the lungs, and hence the fact that the most 

 pronounced lesions of tuberculosis are usually met with in the anterior 

 lobes accords with the above explanation. (In human beings, for reasons 

 as yet not satisfactorily explained, the superior apical lobes are affected 

 most frequently.) 



The great frequency of pulmonary affection does not in 

 itself, however, prove that the infection takes place with the 

 same frequency by way of the respiratory passages. Recent 

 experiments have shown beyond question that the lungs as 

 well as the thoracic lymph glands may be infected from the 

 digestive tract. Chauveau was the first to call attention to this 

 possibility (1868-1872). The latter fed tuberculous material to 



