INFLUENZA THE DISEASE AND ITS EPIDEMIOLOGY 485 



influenza, in its pure and uncomplicated form, consists of the mild, 

 systemic, febrile disease outlined above. It is the causation of this 

 basic condition which constitutes the true etiological problem. The 

 point is to decide whether the influenza bacillus initiates this condition, 

 or whether, like pneumococci, streptococci, and other bacteria, it may 

 not be a secondary invader, preliminary to which there may have been 

 infection by some other agent, perhaps a filtrable virus, which opened 

 the path for the secondary invasion. 



In favor of regarding the influenza bacilli as the primary cause 

 are : The frequent isolation of bacilli from the throats of the earliest 

 cases; the frequency with which these organisms have been isolated 

 from all varieties of early and late complications ; the distribution of 

 the influenza bacilli in the bronchial trees in fatal cases, and their 

 discovery in many cases in pure culture at autopsy ; the wide distribu- 

 tion of the organisms throughout communities at times of epidemic, 

 and their gradually diminishing frequency in normal and diseased 

 respiratory passages as epidemics fade into the past. 



The recent discovery by Parker in our laboratory of the powerful 

 poisons which can be obtained from young influenza cultures, has 

 further given strength to the possibility that the profound prostration 

 and systemic symptoms in an influenza patient might be due to absorp- 

 tion of such poison from even a small focus in the throat. 



Recently, also, Cecil and Blake carried out a series of significant 

 experiments in which they increased the virulence of influenza bacilli 

 by passing them through mice and inoculated these cultures into 

 Philippine monkeys by swabbing them into the nasal mucosa and 

 injecting them into the trachea. They obtained acute respiratory dis- 

 ease, with prostration and subsequent respiratory symptoms, bron- 

 chitis, etc., in these animals. The experiments are not conclusive, since, 

 of course, it was impossible to say that the disease which they pro- 

 duced was analogous to influenza in the human being. Cecil also has 

 carried out similar experiments on human volunteers. The idea under- 

 lying the experiments was the assumption that the virulence of the 

 strains used must be raised to a certain pitch before simple introduc- 

 tion into the nose can lead to typical disease. In his human experi- 

 ments, Cecil obtained moderate, local and systemic symptoms which 

 suggested very mild influenzal attacks. None developed temperature. 

 Other investigators who paid less attention to the virulence of the 

 strains, particularly Wahl, White and Lyall, Bloomfield, Rosenow and 

 McCoy and others, have obtained entirely negative results. 



