374 SPECIFIC MICRO-ORGANISMS 



the food and drink. The virus resists drying for three days, 

 remains alive in water for many weeks and in glycerine for eight 

 days. It is destroyed at 60 to 70 C. in an hour. 



King, Baeslack and Hoffman 1 have found a short, rather thick, 

 actively motile spirochete, Spiroch&ta suis, in the blood in forty 

 cases of hog cholera, together with abundant granules which may, 

 perhaps, represent a stage of this organism. The spirochete has 

 not been found in healthy hogs. It seems probable that this 

 organism may prove to be the causative agent of the disease, but 

 further evidence is necessary to demonstrate this relationship. 



Hog cholera is an extremely contagious disease of hogs, fre- 

 quently fatal, characterized by fever and by ulcerations in the 

 intestine. Immunity follows recovery and is induced artificially 

 by the injection of serum from a hyperimmune hog (passive 

 immunity) and by the injection of such serum together with viru- 

 lent blood from a hog sick with the disease (combined passive 

 and active immunity) . 



The Virus of Dengue Fever. Ashburn and Craig showed in 

 1907 that the virus of this disease exists in the blood of the pa- 

 tients and that it is filterable. The disease is probably trans- 

 mitted by the mosquito Culex fatigans. Apparently the analogy 

 to yellow fever is rather close. 



The Virus of Phlebotomus Fever. Doerr in 1908 demon- 

 strated a filterable virus in the blood of persons suffering from 

 the benign three-day fever of Malta and Crete. The disease is 

 rather widely distributed in tropical countries. It is transmitted 

 by the sand-fly Phlebotomus papatasii. 2 



The Virus of Poliomyelitis. Several investigators, among 

 them r Flexner and Lewis, demonstrated in 1899 the presence of a 

 filterable virus in the central nervous system of patients suffering 

 from infantile paralysis. The virus also occurs in the nasal mucus 

 and in the blood. It survives in glycerine for a month, also re- 

 sists freezing for weeks, and is rendered inert at 45 to 50 C. in 



1 Journ. Infect. Dis., 1913, Vol. XII, pp. 39-47; PP- 206-235. 



2 Birt. Journ. Roy. Army Med. Corps, 1910, Vol. XIV, pp. 236-258. 



