INFLUENZA. 295 



The serum of animals immunized in this way with virulent 

 cultures also protects other susceptible animals. The serum 

 is both antitoxic and bactericidal. The immunity conferred 

 by either of these methods is usually only of short duration 

 about one month ; and is therefore used only as a protective 

 during an epidemic. 



The mortality from plague has been reduced considerably 

 by these methods, and better results are to be expected with 

 the perfection of immunization by cultures of the bacillus. 



Diagnosis : The plague bacillus can always be obtained in 

 large numbers from the suppurating lymph-glands, from the 

 sputum of plague pneumonia, and by puncture from the 

 swollen but intact lymph-glands. In cases of plague septi- 

 caemia the organism is found in the circulating blood and in 

 the organs. 



The films are stained with methylene-blue, when the char- 

 acteristic polar staining is seen. The bacilli very often look 

 like diplococci because of the intensity of the staining of 

 these polar bodies. 



Cultures are made from material obtained from the lesions, 

 which is spread in a thin layer on gelatin plates. The plague 

 bacillus also agglutinates with the blood-serum of persons or 

 animals that have recovered from the disease. This aggluti- 

 nation does not, however, occur before the second week, and 

 is most marked in the second and third weeks. 



Influenza (Bacillus Influenza Bacillus of Pfeiffer). 



The specificity of this germ was established by Pfeiffer in 

 1892, when he succeeded in isolating and making pure cult- 

 ures of Bacillus influenzas from the bronchial secretions of 

 influenza patients. His findings have been confirmed by 

 others, and the organism is accepted as the specific cause of 

 influenza. The peculiar shape of the germ interfered with 

 its earlier discovery. 



Morphology and biology : Bacillus influenzce is a short, thick 

 rod, with rounded ends. It is so short and thick that when 

 two germs are placed end to end they resemble Diplococcus 

 pneumonia?. The occurrence usually is single, but may be 



