24 Modes of Infection. 



before. The cause of the infection must, therefore, be 

 sought in a different direction. The ploblem of the 

 transmission of the virus by the blood-sucking insects 

 naturally suggests itself. In foreign countries experi- 

 ments have been tried to test the theory of insect 

 transmission in the allied diseases (infectious anemia 

 of Europe, swamp fever in America), but no positive 

 results have as yet been obtained. As a matter of 

 fact some investigators disbelieve in such a theory. At 

 present the relationships between the disease and insects, 

 therefore, are obscure. To clear up the question, we 

 performed on a large scale entomological experiments 

 at a section of Izumi pasture, where insects abound. 

 A wire-netting stable and wooden enclosures were con^ 

 structed {vide figures appended at the end of the report). 

 The wire-netting stable is a gigantic cage, so to speak, 

 16,3 m. long, 7.2 m. wide, on one side (north side) of which 

 is a wooden wall, three other sides and the roof being 

 made of fine wire-netting to prevent the access of the 

 insects to the horses within. The wooden enclosure is a 

 rectangular fenced area without a roof, 18.1 m. long, 

 and 10.9 m. wide. Two or three enclosures were con- 

 structed with an interval of about 12.7 m. between them. 

 These were to separate herds. In the above wire- 

 netting stable both healthy horses and the patients were 

 kept together and were watched to see how the infection 

 takes place without interference of insects. 



Experiment I— In 1911 one patient and four healthy 

 horses (Experimental horses Nos. 397, 395, 399, 340) were 

 let in. Two (Experimental horses Nos. 395, 397) become 

 affected after a protracted latent period. The other two 

 remained healthy. 



Experiment II.— In 1912 six very advanced cases and 

 two healthy horses (Experimental horses Nos. 475, 472) 



