Pathoqenesis. 13 



that the causative agent is not of bacterial but of pro- 

 tozoan nature. 



The Resistance of the Virus Against Various 

 Physical and Chemical Conditions. 



I. Heat.— It was demonstrated that the virulent blood 

 heated at a temperature of 60°C. for an hour loses its viru- 

 lence, as was tested by injecting it into healthy horses. 



II. Sun-light.— Two Petri dishes, each containing 

 10 c.c. of the virulent serum, were exposed in the garden 

 of the Institute for Infectious Diseases for two hours 

 between noon and 2 P. M. of August 18 (the day was 

 clear, not a single cloud ; thermometer readings in the 

 room 31°C. and in the sun 49°C.). The serum thus 

 treated was afterward injected into healthy horses with- 

 out any effect whatever. 



III. Cold.— Virulent blood was put in a test-tube 

 and exposed out of doors from December to April in 

 the northern part of Japan (Yamagata Prefecture), during 

 which time the temperature was often as low as -8° or -9° 

 C, and it snowed several times. But that the virus had 

 not lost its vitality, was shown by the fact that of four 

 healthy animals (Experimental horses Nos. 48-51) re- 

 ceiving the blood thus treated all became affected. 



The resistance of the virus against various disin- 

 fectants will be described later on. 



The Retention of the Virus for a Long Time 

 in the Blood of Convalescent Horses. 



Not only can it be demonstrated that the virus of the 

 disease is in the blood at intervals between febrile attacks, 



