Modes of Infection. 23 



experiments. They were, therefore, performed twice, 

 once in 1910 and again in 1912, at Izumi prasture. 

 In 1910 from July 5 to October 31 (119 days) four 

 healthy horses (Experimental horses Nos. 61, 62, 63, 64) 

 were allowed to live with the seven virus-carriers in 

 a special section entirely separated from other herds. 

 All of the subjects contracted the disease. Two years 

 later a similar experiment was tried. For six months, 

 from May 1 to October 31, 1912, four healthy horses 

 (Experimental horses Nos. 471, 486, 492, 493,) were kept 

 with two patients and two virus-carriers. All the horses 

 became affected; the earliest case appeared in 16 days. 

 In comparing the result of these experiments with that 

 of the foregoing (pasturing of healthy horses alone) the 

 difference is very pronounced, and we can hardly escape 

 from the conclusion that the terrible spread of the disease 

 was due to the intermingling of healthy horses with the 

 patients or virus-carriers in the pasture. 



3. How is the virus transmitted from the patients 

 or virus-carriers to healthy animals? The virus is ex- 

 creted in urine, it is true, but in order to induce the 

 disease artificially a large quantity of the urine (repe- 

 tition of the internal administration of more than 100 

 c.c. each time) must be given. Moreover, a large por- 

 tion of the patients' urine would soon find its way into 

 the ground after excreted, and what is left on the 

 surface would be disinfected by the direct sun light. 

 Urine, therefore, can safely be excluded from the causa- 

 tive factors of the transmission of the disease in the 

 pasture. 



To consider the difference between the pasture and 

 the stable, excretion products are more abundant in 

 the latter than in the former. But the proportion of 

 cases appearing is just the reverse, as was described 



