INFLUENZA BACILLUS. 325 



resistance is chosen for the inoculation viz., the brain, 

 upon which the toxic products of the bacillus influenzae 

 acts most powerfully. 



The cell bodies of the bacilli seem to possess consid- 

 erable pyogenic action. 



Immunity. Possibly an immunity for a short period 

 against the influenza poison may be established after an 

 attack. At least in three experiments made by Pfeiffer 

 on monkeys, these animals, after recovering from an 

 inoculation with bacilli, seemed to be much less suscep- 

 tible to a second injection. 



In patients suffering from influenza the bacilli are 

 found chiefly in the nasal and bronchial secretions. 

 In acute uncomplicated cases they may be observed 

 microscopically in large masses and often in absolutely 

 pure culture; the green, purulent sputum derived from 

 the bronchial tubes is especially suitable for examina- 

 tion. The older the process is the fewer bacilli will be 

 found, and the more frequently will they be seen lying 

 within the pus -cells instead of being embedded free in 

 the secretion as at first. At the same time they stain 

 less readily and present more irregular and swollen 

 forms. Very frequently, perhaps almost invariably 

 (Finkler), the influenza process invades portions of the 

 lung tissue. In severe cases a form of pneumonia is 

 the result, which is lobular and purulent in character, 

 and accompanied by symptoms almost identical with 

 bronchopneumonia due to the pneumococcus. The walls 

 of the bronchioles and alveolar septa become densely 

 infiltrated with leucocytes, and the lumina of the bron- 

 chial tubes and alveoli are similarly filled. The pus- 

 cells are found to contain more or less influenza bacilli. 

 There may be partial softening of the tissues, or even 



