INFECTION AND METHOD OF DEVELOPMENT. 179 



infection being not in the tonsils ■' but some portion of the 

 bronchi, the organism either passing along the bronchioles di- 

 rectly to the alveoli or through the walls of the bronchioles to 

 the contiguous tissue of the lungs, giving rise, first, to peri- 

 bronchial and perivascular inflammation in the surrounding 

 tissues, and then to more diffuse inflammatory processes through- 

 out the lung. Having reached the lung tissue, the bacilli rapidly 

 multiply and produce at first pneumonic changes of the lobular 

 type and shortly afterw^ard more general lobar involvement of 

 the lung tissue.' 



The blood becomes quickly infected and a true bacteraemia 

 results in every case. The fact that the bronchial glands at the 

 bifurcation of the trachea are always much more severely af- 

 fected than any of the other lymphatic glands also argues against 

 the theory that epidemic pneumonic plague is primarily a sep- 

 ticsemic disease and that the lungs are infected secondarily from 

 the blood. Moreover, in the earliest stage of the disease, the 

 blood may be free from plague bacilli as we have shown by 

 cultures. 



It is true that in some instances the bacteraemia occurs early 

 in the course of the disease and before hepatization of the lung 

 may have taken place. However, microscopical examination 

 will reveal enormous numbers of plague bacilli in the engorged 

 lung tissue from which it appears that the origin of the bacte- 

 raemia is clear. 



The tonsils may become secondarily infected in pneumonic 

 plague just as other lymphatic glands — for example, the bron- 

 chial ones — become so infected. However, in pneumonic plague 

 death usually occurs before any marked macroscopic changes 

 occur in the tonsils. There is no doubt also that the tonsils may 

 become primarily infected in epidemics of pneumonic plague 

 just as has occurred in sporadic cases in epidemics of bubonic 

 plague; such cases have been previously reported. This, how- 

 ever, is not the common channel of primary infection, and in 

 such cases involvement of the glands of the neck occurs early 

 in the course of the disease. Such cases are really instances of 

 bubonic plague in which the lungs may, or may not, become 

 secondarily infected. 



In some instances plague infection may occur directly through 



" See also under pathological anatomy, p. 215 of this report for the 

 condition of the tonsils in the human cases and Plates XI and XVIII. 

 * See Plate VII, figs. 2 and 3, and Plates IX and X. 



