MICROBIAL DISEASES OF MAN AND ANIMALS. 657 



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

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

 terium 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 in- 

 crease the mortality from the disease. B. cholera suis is a small, very 

 actively motile, non-spore-bearing bacillus with rounded ends, which 

 stain 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 re- 

 action at first; this changes after a week or more to an alkaline reaction. 

 Gas is produced in bouillon containing dextrose, but lactose and sac- 

 charose are not affected. Rabbits and guinea pigs succomb within four 

 to ten days to small doses of this organism. Hogs are much more refrac- 

 tory. It is only after the administration 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 consider- 

 able 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 confined 

 to South Africa. It is most prevalent in summer and appears to be trans- 

 mitted by the bite of an insect, as it is not contagious but may be com- 

 municated to susceptible horses through blood inoculations. This disease 

 manifests itself by producing severe inflammatory changes in the lungs and 

 in the tissues of the head and neck and is attended by a high mortality. 

 No visible organism has been found which will produce horse sickness and 

 as McFadyean and Nocard have shown that the virus is capable of pass- 

 ing through the finest bacteria-proof filters, this disease is probably caused 



* Prepared by M. Dorset. 

 42 



