322 BACTERIA PATHOGENIC TO MAN 



Morphology. Very small, moderately thick bacilli (0.2 to 0.3// in 

 thickness to 0.5 to 1.5/* in length), usually occurring singly or united 

 in pairs, but threads or chains of three, four, or more elements, are 

 occasionally found. No capsule has been demonstrated. 



Staining. The bacillus stains with difficulty with the ordinary aniline 

 colors best with dilute ZiehPs solution (water 9 parts to ZiehPs solution 

 1 part), or Loeffler's methylene-blue solution, with heat. When faintly 

 stained the two ends of the bacilli are sometimes more deeply stained 

 than the middle portion. They are not stained by Gram's method. 



Biology. An aerobic, non-motile bacillus; does not form spores; no 

 growth occurs with most cultures below 26 C., or above 34 C., or in 

 the entire absence of oxygen. 



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

 surface of ordinary nutrient culture media containing haemoglobin. Plain 

 or glycerin agar, or blood serum thinly streaked with rabbit or human 

 blood, make the best media for their growth. At the end of eighteen 

 hours in the incubator very small circular colonies are developed, 

 which, under a low magnification (100 diameters), appear as shining, 

 transparent, homogeneous masses, and even under a No. 7 lens scarcely 

 show at all the individual organisms. Older colonies are sometimes 

 colored 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 nutrient agar they may become confluent. Transplantation of 

 the original culture to ordinary agar or serum cannot, as a rule, be 

 successfully performed, owing to the want of sufficient haemoglobin; 

 but if sterile rabbit, pigeon, or human blood be added to these media 

 transplantation may be indefinitely performed, provided it is done 

 every three or four days. Cultures may remain alive up to seventeen 

 days in the ice-chest. By a series of beautifully carried out experiments 

 Pfeiffer showed that not only were the red blood cells the necessary 

 part of the blood needed for the growth of the influenza bacillus, but 

 that it was the haemoglobin in the cells. 



In bouillon in thin layers, to which blood is added, a good develop- 

 ment takes place if there is free access of oxygen. 



RESISTANCE AND LENGTH OF LIFE. The influenza bacillus is very 

 sensitive to desiccation; a pure culture diluted with water and dried 

 is destroyed with certainty in twenty-four hours; in dried sputum the 

 vitality, according to the completeness of drying, is retained from 

 twelve to forty-eight hours. It does not grow, but soon dies in water. 

 The thermal death point is 60 C. with five minutes' exposure (Pfeiffer 

 and Beck). In blood-bouillon cultures at 20 C. they retain their 

 vitality for from a few days to two or three weeks. In moist sputum 

 it is difficult to determine the duration of their life, since the other 

 bacteria overgrow and make it impossible to find them. It is probable 

 that they can remain alive for at least two weeks. The bacilli are very 

 readily killed by chemicals, disinfectants, and succumb to boiling 

 within one minute and to 60 C. within ten minutes. 



