564 INFECTION AND IMMUNITY. 



Bacillus During the epidemic just cited a number of or- 

 ganisms were erroneously described as the cause of 

 the disease. In 1892, however, Pfeiffer discovered 

 a minute bacillus which he found constantly and 

 in large numbers in the sputum of influenza pa- 

 tients only. The observations of Pfeiffer have 

 been confirmed by a large number of investigators, 

 and the organism, Bacillus influenza?, is now ac- 

 cepted as the cause of the disease. It is one of the 

 smallest of bacteria (0.2 or 0.3 by 0.5 microns), is 

 non-motile and forms no spores. A medium con- 

 taining blood or hemoglobin is essential for its 

 artificial cultivation, and even under the best con- 

 ditions it grows meagerly and slowly. A number 

 of bloods, but particularly those of man and the 

 pigeon, favor its growth. It is a strong aerobe. 

 The organism is best stained by a dilute solution of 

 carbol-fuchsin (1 to 10), and, like the plague 

 bacillus, exhibits polar staining, i. e., the ends 

 stain more deeply than the central portion. 

 Symbiosis. When the staphylococcus and some other organ- 

 isms are grown in mixed culture with the influ- 

 enza bacillus, the latter is stimulated to a more 

 vigorous growth. According to Jacobsohn, killed 

 cultures of the streptococcus greatly increase the 

 virulence of the influenza bacillus when the mix- 

 ture is injected into animals. 



Psendo- Pfeiffer designates as pseudoinfluenza bacilli a 

 In Bacfii* number of influenza-like organisms which have 

 been found in man and animals. They have the 

 morphology of the influenza bacillus, are a little 

 larger, and also prefer a medium which contains 

 hemoglobin, but since some of them occur in ani- 

 mals which are known not to be susceptible to in- 

 fluenza, it is concluded that they can not be identi- 



