Modes op Inpectiok. 21 



Station of the Agricultural College, Tokyo Imperial tJni- 

 versity. One of them was infected, and the other two 

 showed negative result. 



3. For about ten months, from May 1911 to Feb- 

 ruary 1912, two horses (Experimental horses Nos. 105, 

 115) were kept with a patient at the Institute for In- 

 fectious Diseases. Neither of them became ill. 



From the above experiments we can reach the con- 

 clusion that infection very rarely occurs in the stable. 

 This result agrees with that of another experiment car- 

 ried on in a stable from which the access of insects 

 was prevented by means of wire-netting {vide the next 

 section). 



D. Infection in Natural Environment. 



Several experiments were performed in the open air to 

 determine the actual course of transmission of the disease. 

 The following are the main problems to be solved : 



1. Does the virus winter in pasture ? 



2. How does infection take place when healthy 

 animals are kept with patients or virus-carriers in the 

 same pasture? 



3. How is the virus transmitted from one horse to 

 another in pasture? 



4. How is the disease related with blood-sucking 

 insects ? 



In order to solve the above questions pasturing ex- 

 periments were carried on during four summers (1909- 

 1913). Their progress and results therefrom are as 

 follows : 



1. It had long been known that terrible infection 

 of the disease took place in pasture, but we did not 

 have any information regarding the length of time of 



