Mind and body are two parts of a complex organism controlled by the nervous system, which acts on information received from the senses. The way a person perceives and reacts depends on his mood, his state of health, his diet, his body temperature and his level of consciousness. 2. There is considerable evidence that every thought or emotion has some related physical effect, and that every change within the nervous system should have some psychological effect. Although the precise nature of these correlations is not always known, the view that body and mind are constantly interacting in some way is now accepted by most psychologists. 3. The relationship between mind and body is particularly apparent in emotional states, especially those of fear and anger. When a person is in the grip of a powerful emotion his body undergoes changes, just as it does when he is asleep, ill or under the influence of drugs or alcohol. Most people are familiar with such sensations as a dry mouth when they are nervous, or a racing heart when they are afraid or excited. Such physical changes can be measured, for instance, by recording pulse rate and breathing, or by measuring the dilation of the pupils of the eyes. 4. a particularly sensitive measure of bodily change during periods of emotion is the galvanic skin response(GSR). This is used in the instrument known as the lie detector. The GSR depends on the fact that some mental activity produces bodily changes, such as sweating, which affect the skin's resistance to electricity. To measure GSR, electrodes are placed on the palm and on the back of the hand, and a weak current is passed between the electrodes. Changes in the current are recorded in an amplified form, often by means of an automatically controlled pen on moving paper. Other recordings, for instance of pulse, blood pressure and breathing, can be made simultaneously, by an instrument called a polygraph. 5. The galvanic skin response method has proved a very efficient indicator of general psychological arousal. Even slight embarrassment will cause a defection of the recording pen.