298 YELLOW FEVER; BUBONIC PLAGUE; INFLUENZA. 



The bacilli may remain latent in the secretions for months 

 after recovery from the disease has apparently been complete, 

 and under favorable conditions again become virulent. 



Immunity: One attack of influenza undoubtedly confers 

 immunity, but unfortunately it is of short duration. In fact, 

 it would appear that when the immunity has disappeared the 

 individual is even more susceptible to the disease than before 

 the first attack. Persons have been attacked several times 

 during the course of the same epidemic. Owing to the insus- 

 ceptibility of animals to influenza, it has been impossible to 

 immunize them, and thus, perhaps, obtain a serum which 

 could be used for immunizing or curative purposes. 



The bacillus is responsible for the lesions, and is always 

 found at the seat of the disease ; it does not produce a toxin 

 which is absorbed. 



Diagnosis : The bacteriologic diagnosis is readily made from 

 the nasal secretions and the bronchial mucus. A slide can 

 be prepared, stained, and examined immediately. The pecu- 

 liar appearance of the germ and its behavior to stains are 

 absolutely characteristic. Cultures may be made on blood- 

 serum or other media smeared with blood, haemoglobin, or 

 sputum, which always contains corpuscles. 



It should be borne in mind that the influenza bacillus may 

 be the cause of conditions other than those which are looked 

 upon as distinctive of this disease. During severe epidemics 

 of influenza it is not uncommon to see typical cases of lobar 

 pneumonia which are due to the influenza bacillus and not to 

 the pneumococcus. It is important to determine the cause 

 of such a pneumonia, as it will influence the treatment con- 

 siderably. The serum treatment of pneumonia could not be 

 used in influenza pneumonia, and the prognosis in the latter 

 is much worse than in a pneumococcus pneumonia. 



The influenza bacillus may be confounded with another 

 organism which Pfeiffer found in the sputum of cases of 

 bronchopneumonia, and which he named the pseudo-influenza 

 bacillus. This organism differs in culture in that it exhibits 

 a marked tendency to form very long filaments. It is also 

 somewhat longer than the true bacillus. Otherwise the re- 

 semblance between the two is very close. 



