BACTERIUM INFLUENZA. 333 



demic appearance on eighty-six different occasions. Its 

 first appearance in this country was in Massachusetts in 

 1627 ; since that time there have been twenty -two vis- 

 itations of influenza to the United States. The pan- 

 demic of 1889-'90, the most severe for a long time, 

 appears to have originated in Central Asia and to have 

 spread pretty much over the entire civilized world. The 

 advent of influenza in a community is always remark- 

 able for its astonishing rate of transmission from per- 

 son to person and its dissemination over wide areas. 



During the recent pandemic investigations having 

 for their object the discovery of its cause were insti- 

 tuted, with the result of demonstrating in the catarrhal 

 secretions from the air-passages a micro-organism that 

 is claimed to stand in causal relation to influenza. 



By appropriate methods of staining it is also fre- 

 quently possible to demonstrate the presence of this 

 organism in the secretions of the nose, mouth, and throat 

 of apparently healthy persons, as well as in those from 

 persons suffering from such diseases as diphtheria, scar- 

 let fever, measles, etc. 



This organism, bacterium influenzae, as it is called, was 

 discovered, isolated, cultivated, and described by R. 

 Pfeiffer. 



It is a very small, slender, uon-spore-forming, non- 

 motile, aerobic bacillus, occurring singly and in pairs, 

 joined end to end. It stains with watery solutions of 

 the ordinary basic aniline dyes ; somewhat better with 

 alkaline methylene-blue, but best when treated for five 

 minutes with a dilution of ZiehPs carbol-fuchsin in 

 water (the color of the solution should be pale red). 

 (Fig. 63.) It is decolorized by the method of Gram. 



It develops only at temperatures ranging from 26 



