MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 863 



cholera. As a result of this blood treatment their serum acquires the 

 power to protect non-immunes. Injections of serum from hyper- 

 immunized animals confers a passive immunity, while the simultaneous 

 injection of serum with a small amount of virus produces an active 

 immunity. 



BACILLUS CHOLERA Suis (B. suipestifer). No description of the 

 etiology of hog cholera would be complete without a reference to this 

 bacterium which was long regarded as the cause of hog cholera. It is 

 found after death in the blood and organs of the majority of hogs 

 affected with hog cholera and in this role of secondary invader it no 

 doubt tends to increase the mortality from the disease. B. cholera 

 suis is a small, very actively motile, non-spore-bearing bacillus with 

 rounded ends, and stains readily with the ordinary aniline dyes. It 

 does not stain by Gram's method. This organism is easily cultivated 

 on the ordinary media; gelatin is not liquefied; milk is not coagulated 

 but acquires an acid reaction at first; this changes after a week or more 

 to an alkaline reaction. Gas is produced in bouillon containing 

 dextrose, but lactose and saccharose are not affected. Rabbits and 

 guinea pigs succumb within four to ten days to small doses of this 

 organism. Hogs are much more refractory. It is only after the ad- 

 ministration of large doses that they show any symptoms of illness 

 following subcutaneous injections. By feeding pure cultures of B. 

 cholera suis or by injecting these intravenously a considerable number 

 of hogs will succumb and at autopsy present lesions which correspond 

 quite closely to those seen in naturally acquired cases of hog cholera. 

 There are, however, certain important differences between the disease 

 produced by B. cholera suis and the natural disease hog cholera. For 

 example, hogs infected with B. cholera suis do not transmit the disease 

 to other hogs by contact. The blood of hogs infected with B. cholera 

 suis does not produce disease when injected subcutaneously into 

 other hogs, and, in addition, hogs which recover from illness produced 

 by injections or feedings of pure cultures of B. cholera suis have no 

 immunity against the natural disease hog cholera. 



HORSE SICKNESS* 



This disease affects the equine species only and appears to be con- 

 fined to South Africa. It is most prevalent in summer and appears to 



* Prepared by M. Dorset. 



