26 Modes of Infection. 



Experiment I. may be sought in the fact that in the 

 former the virus was rather rare in the patients' en- 

 closure. 



Experiment III— In 1913 the above experiment was 

 repeated extending from May 1 to October 31. Nine 

 patients were received in one enclosure. Two healthy 

 horses (Experimental horses Nos. 552, 564) were kept in 

 the enclosure A during the experiment and in the en- 

 closure B four horses (Experimental horses Nos. 572, 573 

 565, 634) were let in, two at a time. The process of 

 the infection was carefully watched. The result was 

 very striking, all the healthy animals contracting the 

 disease. 



The above three experiments clearly demonstrate 

 that the disease can be transmitted without intercourse 

 between the healthy and sick horses, when free access 

 of insects is not prevented, and that under such circum- 

 stances the infection goes on in a degree as fierce as in 

 the mixed pasturing. From this, the conclusion may be 

 drawn that the transmission of the disease under con- 

 sideration is accomplished only through the agency of 

 insects that are capable of flying. 



4. The insects and their allies, which occur in pas- 

 tures and attack animals, are as follows : ticks, bot-flies, 

 sand-flies, mosquitoes, horse-flies etc. 



A. Ticks (Ixodidae)— Ticks have no power of flying 

 and moreover if these parasites on the patients be trans- 

 ferred to the healthy horses, the latter do not become 

 sick at all. 



B. Bot-flies {Gastrophilus equi) — These do not 

 belong to the blood-sucking insects, but since its larvae 

 are found in the horse's stomach, the virus may thus 

 be taken from the sick horses and transmitted to the 

 healthy. To exclude the possibility several larvae were 



