226 THE INFECTIOUS DISEASES. 



Early in 1892 Pfeiffer, Kitasato, arid Canon described the occurrence 

 in the bronchial exudate and in the blood of influenza patients of a very 

 small bacillus, hitherto unknown or possibly noted earlier by Babes. 

 This bacillus B. influenzas was sometimes present in the bronchial exu- 

 date in enormous numbers, and often with little or no contamination 

 with other germs. It was found at the seat of other local lesions, and the 

 pus cells often contained many bacilli. In the blood it was occasionally 

 present. It has been found to persist in the body long after the active 



Characters of the Influenza Bacillus. 



The influenza bacillus stains with some difficulty with the simple anilin dyes; but 

 by Ziehl's solution (page 247), or by warmed Loffler's methylene blue (page 154), it is 

 readily colored. It does not retain the stain well by Gram's method. The bacilli are 

 slender and short (one to one and a half times as long as broad) with rounded ends, 

 sometimes lie singly, sometimes in pairs or short chains or heaps, do not fonn spores 

 and are not motile. The organism apparently dies after a few hours' drying in the air 

 and soon in water. , 



This bacillus grows best at body temperature, on glycerin-agar whose surface has 

 been smeared with blood human, rabbit, or pigeon. It forms very small, scarcely vis- 

 ble dewdrop-like colonies, which, although growing close together, do not tend to coal- 

 esce, as many micro-organisms do. It does not grow at a temperature at which the 

 nutrient gelatin remains solid. In beef tea it forms a scanty, cloudy growth. It has 

 been cultivated through several generations, but usually dies soon. Animal inoculations 

 have given diverse and not very marked results. The earlier observations have been in 

 general confirmed by later studies of others, but the frequency of its occurrence in the 

 blood has been questioned. 



The evidence that the organism described above is the excitant of 

 influenza rests largely upon its apparently constant presence, especially 

 in the exudates. Its effects in the body are most commonly induced 

 through its toxins. That the organism should have been occasionally 

 found under other conditions 11 does not at all militate against its signifi- 

 cance in inciting the manifestations of influenza, since many parallel in- 

 stances are known in other infectious diseases. The frequent discrep- 

 ancy between the clinical and bacterial diagnosis in influenza is largely 

 due to its varying and often obscure clinical manifestations which render 

 possible and convenient the use of the name for many phases of catarrhal 

 and other forms of inflammation. 



Other Organisms of the Influenza Bacillus Group. 



There are several organisms in the influenza bacillus group which considerably re- 

 semble it, some of which appear to be pathogenic, others not so. Thus several ob- 

 servers have found in exudates from various sources, but especially in the respiratory 

 passages, small immobile asporogenous bacilli growing best under conditions similar 

 to those favorable to the influenza germ, the colonies being similar. They are some- 



1 For a full resume of the characters of the influenza bacillus and its relation to 

 various forms of the disease, with bibliography, see the articles by Beck in Kolle and 

 Wassermann's "Handbuch der Mikroorganismen," Bd. ii., p. 359. 



* See Park, "Bacteriology in Medicine and Surgery," p. 326. 



