194 INFLUENZA. 



organism which they believed, with apparent correctness, to 

 be the cause of the disease. 



Morphology. The bacillus so isolated may be described as 

 follows : a small, thick rod, occurring singly or in pairs, 

 stained with difficulty by the ordinary anilin dyes, but fairly 

 well with a diluted Ziehl solution or Loeffler's methylene- 

 blue ; not stained by Gram's method. The body of the rod 

 stains less well than the ends. It has no flagella and contains 

 no spores. (Plate IV.) 



Biologic Characters. The bacillus of influenza is strictly 

 aerobic, not growing at all without oxygen. It is non-motile, 

 and grows at a temperature between 26 and 43 C. 



It grows but rather poorly in all media that may be sub- 

 mitted to this temperature, unless the surface of the media 

 be smeared over with fresh sterilized blood, when the growth 

 is quite luxuriant. On glycerin-agar or in blood-serum tubes 

 on which fresh rabbit's blood has been smeared, it grows as 

 transparent watery colonies, resembling very much dew- 

 drops. Pigeon blood seems even better. The colonies have 

 no tendency to coalesce. In bouillon to which a little fresh 

 blood has been added it grows luxuriantly. It does not 

 cause clouding of the medium, but its colonies are seen as 

 little flakes adhering to the sides of the tube and forming a 

 deposit at the bottom. 



Vitality. The bacillus of influenza is destroyed in two or 

 three hours by drying. It has very little resisting power, 

 and in water lives scarcely twenty-four hours. In pneu- 

 monia occurring during the course of this disease the bacilli 

 are often found in the body of the leucocytes. 



Pathogenesis. Outside of the human race none of the 

 lower animals seems to be susceptible to the disease, excepting 

 perhaps the monkey, and by inoculation it is difficult to 

 produce any symptom in laboratory animals. In man, how- 

 ever, the bacillus is constantly found in the bronchial and 

 nasal secretions, also in the pneumonic patches so often found 

 in the course of this disease. At autopsies it has been found 

 also in the spleen and occasionally in the blood. Some per- 

 sons have a natural power of retaining live bacilli in the 



