Immunity 465 



Pathogenesis. — The bacillus is pathogenic for very few of the 

 laboratory animals. The guinea-pig is susceptible of fatal infec- 

 tion, the dose required to cause death varying considerably. 



Pfeiffer and Beck* produced what may have been influenza in 

 monkeys by rubbing their nasal mucous membranes with pure 

 cultures. 



Immunity. — ^As influenza is a disease that commonly relapses, and 

 from which one rarely seems to acquire protection against future 

 attacks, there must be scarcely any immunity induced through ordi- 

 nary infection. Moreover, the organism once finding its way into 

 the body seems to remain almost indefinitely, especially when, as in 



Fig. 176. — Bacillus of influenza; cover-glass preparation of sputum from a case 

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



pulmonary tuberculosis, there is already present an abnormal con- 

 dition furnishing discharges or exudates in which it can thrive. 



Delius and Kollef found that the toxicity of the culture does not 

 depend upon a soluble toxin, but upon an intracellular toxin. The 

 outcome of the researches, which were made most painstakingly, was 

 total failure to produce experimental immunity. 



Increasing doses of the cultures, injected into the peritoneal 

 cavity, enabled the animals to resist more than a fatal dose, but never 

 enabled them to recover when large doses of living cultures were 

 administered. 



A. Catanni, Jr., J trephined rabbits and injected influenza toxin 



* "Deutsche med. Wochenschrift," 1893, xxi. 



t "Zeitschrift fiir Hygiene," etc., Bd. 1897, xxrv, Heft 2. 



t Ibid., Bd., 1896, xxm. 



