The theory of the emotions has been radically transformed by the discovery of the part played by the ductless glands. Cannon’s _Bodily Changes in Pain, Hunger, Fear and Rage_ is a book whose teaching has come to be widely known, though not more so than its importance warrants. It appears that certain secretions from the glands into the blood are the essential physiological conditions of the emotions. Some people say that the physiological changes correlated with these secretions _are_ the emotions. I think this view must be received with some caution. As everyone knows, the adrenal glands secrete adrenin, which produces the bodily symptoms of fear or rage. On one occasion my dentist injected a considerable amount of this substance into my blood, in the course of administering a local anæsthetic. I turned pale and trembled, and my heart beat violently; the bodily symptoms of fear were present, as the books said they should be, but it was quite obvious to me that I was not actually feeling fear. I should have had the same bodily symptoms in the presence of a tyrant about to condemn me to death, but there would have been something extra which was absent when I was in the dentist’s chair. What was different was the cognitive part: I did not feel fear because I knew there was nothing to be afraid of. In normal life, the adrenal glands are stimulated by the perception of an object which is frightful or enraging; thus there is already a cognitive element present. The fear or rage attaches itself to the object which has stimulated the glands, and the full emotion arises. But when adrenin is artificially administered, this cognitive element is absent, and the emotion in its entirety fails to arise. Probably if it were administered in sleep it would produce a dream of terror, in which the dreamer’s imagination would supply an object for fear. The same thing might happen on waking life with animals or young children. But with an adult of average rationality, the knowledge that there is nothing to be afraid of inhibits the full development of the emotion. Fear and rage are both active emotions, demanding a certain kind of behaviour towards an object; when this behaviour is obviously not called for, it is impossible to feel either emotion fully. There are, however, other emotions, such as melancholy, which do not demand an object. These, presumably, can be caused in their entirety by administering the proper secretions. A disordered liver may cause melancholy which is not relieved by knowledge of its source. The emotions which do not require an object are those which do not call for any appropriate line of action. Emotions are subject to “conditioning”, so that the stimuli which call them out become more various as a result of experience. Dr. Watson has found only two original stimuli to fear in young infants, namely loud noises, and lack of support; but anything associated with either of these may become terrifying.