INFLUENZA BACILLUS. 321 



Morphology. Very small, moderately thick bacilli, 

 usually occurring singly or united in pairs, but threads 

 or chains of three, four, or more elements, are occa- 

 sionally found. 



The bacillus stains with difficulty with the ordinary 

 aniline colors best with dilute ZiehPs solution or 

 Loffler's methylene-blue solution, with heat. When 

 faintly stained the two ends of the bacilli are some- 

 times more deeply stained than the middle portion. 

 Those we have examined, all obtained from cases in 

 New York, were not stained by Gram's method, but 

 some report instances in which they were. 



Biological Characters. An aerobic, non-motile bacil- 

 lus; does not form spores; no growth occurs below 

 26 C., or above 43 C., or in the entire absence of oxy- 

 gen. This bacillus is best cultivated at 37 C., and on 

 the surface of the ordinary nutrient culture media con- 

 taining haemoglobin or purulent material. Plain or 

 glycerin-agar, or blood-serum streaked with sputum, 

 pus, or blood, make a good soil for their growth. At 

 the end of eighteen to twenty-four hours in the incu- 

 bator very small, drop-like colonies are developed, 

 which, under a low magnification (100 diameters), ap- 

 pear as shining, transparent, homogeneous masses, and 

 even under a No. 7 lens scarcely show at all the indi- 

 vidual organisms. Older colonies are sometimes col- 

 ored yellowish-brown in the centre. A characteristic 

 feature of the influenza bacillus is that the colonies tend 

 to remain separate from each other, although when they 

 are thickly sown in a film of moist blood upon nutri- 

 ent agar they may become confluent. Transplantation 

 of the original culture to ordinary agar or serum can- 

 not, as a rule, be successfully performed, owing to the 



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