The following facts were obtained by experiments about the relation between the inoculated mice or spirochaete recurrens and the temperature, light and darkness: 1) The length of the incubation period varies in accordance with the condition of the inoculated mice with spirochaete recurrens, that is in case it is heated (33-36°C), or refrigerated (6-8°C), or kept in the sunshine, in the darkness and in the room. 2) When heated, the incubation period is shorter than any other case, and when refrigerated, it is the longest of all. The mice being kept in the room or in the dark room, the incubation period is nearly the same. When the mice is exposed in the sunshine, the period seems to be longer than the experiment in the dark room on many occasions. 3) Spirochaete recurrens itself has a certain resisting power to the temperature, darkness and light; namely, its resistance is weak to the high temperature and sunshine but it has the longest life in the room. To the refrigeration its resistance is comparatively strong. 4) In the experiment of the inoculated mice, the increase of spirochaete is comparatively remarkable, in case the mice is heated. On the other hand, the increase is slow when refrigerated. As for me, in the spirochaete recurrens experiment the resistance is weak when heated, and strong when refrigerated. Thus, the result of the inoculated experiment apparently seems to be contrary to the spirochaete recurrens.