Abstract: The change of potential difference of the human body caused by psychological factors and those occurred under different psychological states, e.g., exitment, calm and sleep, were observed with the aid of a potentiometer. The results obtained are as follows:1. The potential difference of the human body varies with different regions, being relatively higher between the parts near the trunk and the foot than that between the parts near the ends of the extremities and the foot; the maximum value of the potential difference is about 60mV, its maximum change being 40mV.2. The potential difference decreases when the subject changes from a working state to a resting state, and further decreases as sleep takes place, while it increases again as soon as the subject awakes.3. The potential difference also becomes higher when emotional tension appears as the result of sudden irritation, and resumes its original level when the subject calms down. Within a definite limit, the greater the tension is, the more markedly the potential difference will increase.4. It is the psychological tension that determines the potential difference of the body surface, though the physical status may make some difference. The authors are of the opinion that the potential difference from the body surface is a reliable indicator of the extent of emotional tension of human beings.

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