INFLUENZA. 



569 



The bacillus is pathogenic for certain of the laboratory 

 animals, the guinea-pig in particular being subject to 

 fatal infection. The dose required to cause death of a 

 guinea-pig varies considerably, in the immunization ex- 

 periments of Deline and Kole 1 ^ of a 24-hour old culture 

 being fatal in twenty- four hours. They found that 

 the toxicity of the culture does not depend upon a 

 soluble toxin, but in something retained in the bod- 

 ies of the bacilli. The outcome of the researches, which 



.-'-' 



&$& 7& 



Fig. 132. — Bacillus of influenza; cover-glass preparation of sputum from a case 

 of influenza, showing the bacilli in leukocytes; highly magnified (Pfeiffer). 



were made most scientifically and painstakingly, was 

 the total failure to produce immunity. Increasing 

 doses of the cultures injected into the peritoneum re- 

 sulted in enabling the animals to resist rather more 

 than a fatal dose, but never enabled them to main- 

 tain vitality when large doses were administered. This 

 discovery is in exact harmony with the familiar clinical 

 observation that, instead of an individual being immune 

 after an attack of influenza, he is as susceptible as before, 

 if not more so. 



1 Zeitschrift fur Hygiene, etc., Bd. xxiv., 1897, Heft. 2. 



