426 AGKICULTURAL AND INDUSTRIAL BACTERIOLOGY 



such an animal when injected with 2 cubic centimeters of 

 virulent blood. 



In practice the hog cholera antiserum is used either for 

 conferring a temporary passive immunity or combined with 

 the injection of virus for the conferring of an active im- 

 munity. In the latter method, the antiserum together with 

 the virulent blood are injected into the animal to be im- 

 munized. The immunity thus secured is relatively per- 

 manent, while immunity secured by the injection of anti- 

 hog cholera serum alone is relatively temporary, lasting 

 only from 4 to 6 weeks. As a result of the utilization of 

 this method the losses from hog cholera have been greatly 

 reduced. 



INFLUENZA 



The disease influenza is an acute infection of man which 

 has. swept in a great pandemic around the world in recent 

 years. The ordinary form shows an onset of severe head- 

 ache, accompanied by pains and aches in the back, by fever 

 and by general prostration. The fever continues in such 

 cases from 3 to 5 days and finally leaves the patient 

 exhausted. 



Pfeiffer in 1892 described an organism which he believed 

 to be the cause of the disease influenza. This has been 

 generally assumed to be the cause until investigation in the 

 past few years failed to prove any causal relationship 

 between this organism and the disease. While much work 

 has been done upon the disease, the causal organism has 

 not yet been isolated with certainty. 



The disease is important not only in itself but because it 

 is followed in a considerable proportion of cases by severe 

 and frequently fatal pneumonia. 



SWAMP FEVER OR INFECTIOUS ANEMIA 



This disease has been known for many years in Europe 

 and more recently has been studied in North America. It 



