INFLUENZA. 449 



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 ^V of a 24-hour old culture 

 being fatal in twenty-four hours. These scholars found 

 that the toxicity of the culture resides not in a soluble 

 toxin, but in the bodies of the bacilli. The outcome of 

 the researches, which were made most scientifically and 



FIG. 127. bacillus of influenza; cover-glass preparation of sputum from a case 

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



painstakingly, was the total failure to produce immunity. 

 Increasing doses of the cultures injected into the peri- 

 toneum resulted 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. 

 29 



