The pathohistological changes of mice organ tissues were observed on the inoculation of ectromelia virus in the various changes of inoculated method and region. And the results were as follows. 1. The acute course was observed on the intraperitoneal inoculation, but it was subacute on the peroral and pernasal inoculation or the inoculation into the foot-sole. 2. The pathological changes of liver and spleen were diffuse on the intraperitoneal and peroral inoculation and it was local on the pernasal and subcutaneous inoculation or the in oculation into the foot-sole. 3. The change of intestine was the most remarkable on the peroral inoculation and the change of lung was the most remarkable on the pernasal inoculation. 4. The changes of organ tissues, other than those organs, were common to both of the occasions. 5. The presence of diffuse change in the organ was related to the density of invaded virus into organ and it was thought that the ectromelia virus was diluted by the systemic circulation. 6. The changes of liver and spleen were diffuse like epidemic hepatitis in human on the peroral administration and it was thought that bone of them showed a common infectious course.