EPIDEMIOLOGY OF INFLUENZA 499 



flattening out on the bottoms of the cages, muscular weakness and 

 death in a considerable percentage of the cases within two to six 

 hours. A characteristic feature is the incubation time which is 

 regularly between forty-five minutes and one hour and one-half. 

 These poisons have been studied in parallel series with similarly 

 produced streptococcus and typhoid filtrates by Zinsser, Parker and 

 Kuttner 30 and belong to a class of substances probably non-specific 

 and non-antigenic, described by us as "X" substances, the exact 

 nature of which is at present uncertain. 



INFLUENZA BACILLI NOT ASSOCIATED WITH EPIDEMIC INFLUENZA. 

 The question of the etiological relationship of the influenza bacillus 

 to the epidemic disease has been sufficiently discussed above. It is 

 an important fact that the influenza bacillus is a common respiratory 

 invader of man in the interepidemic periods, and without any 

 apparent relationship to the typical epidemic disease. Subsequent 

 to the epidemic of 1889, its wide distribution was established by a 

 multitude of investigations. Pfeiffer 31 noted its frequent presence 

 in tuberculous processes in his early studies, and this observation 

 was confirmed by many others. It is especially frequent in bron- 

 chiectatic cavities. Boggs 32 reported a number of such cases in 

 which influenza bacilli were present symbiotically in the cavity fluids 

 in cases that showed negligible symptoms. A number of observers 

 have isolated influenza bacilli from the blood in cases that had died 

 of other conditions. Jaehle 33 obtained the bacilli from the heart's 

 blood at autopsy from two scarlet fever cases. He also found the 

 organisms in blood culture at autopsy in fifteen cases of measles. 

 In one of these cases the influenza bacillus was present when the 

 only other influenza bacillus lesion present was a tonsillar infection. 

 He also found the organisms in the blood five times in nine cases 

 of chickenpox, and twice in twenty-four cases of whooping cough. 

 He found them in the respiratory passages in fifteen cases of diph- 

 theria. Wynekoop 34 has made similar studies, especially in con- 

 nection with lesions of the larynx, and in chronic laryngitis he found 

 the organisms in pure culture. He described a special form of severe 

 tonsillitis due to the influenza bacillus. Some of these were clinically 



30 Zinsser, Parker and Kuttner, Jour. Exper. Biol. and Med., 18, 1920, 49. 



81 Pfeiffer, Deut. med. Woch., 18, 1892, 28. 



32 Boggs, 130, 1905, 902. 



83 Jaehle, Zeit. f . Heilkd., 22, 1901, 190. 



34 Wynelcoop, Jour. A. M. A., 40, 1903, 574. 



