Bearing of modern psychology on the sex problem; Conditioning of the sexual impulse; Vicarious expression of the sexual impulse; Unconscious factors of the sex life; Taboo control has conditioned the natural biological tendencies of individuals to conform to arbitrary standards of masculinity and femininity; Conflict between individual desires and social standards. An adequate treatment of the sex problem in society must necessarily involve a consideration of the sexual impulse in the individual members of that society. Recent psychological research, with its laboratory experiments and studies of pathology has added a great deal of information at this point. The lately acquired knowledge of the warping effect of the environment upon the native biological endowment of the individual by means of the establishment of conditioned reflexes, the discovery that any emotion which is denied its natural motor outlet tends to seek expression through some vicarious activity, and the realization of the fundamental importance of the unconscious factors in shaping emotional reactions,--such formulations of behaviouristic and analytic psychology have thrown a great deal of light upon the nature of the individual sex life. There are certain modifications of the erotic life which are explicable only when we recollect that under environmental influences situations which originally did not call up an emotional response come later to do so. This fact, which was first noted by Setchenov, was experimentally demonstrated by Pavlov and his students.[7] They found that when some irrelevant stimulus, such as a musical tone or a piece of coloured paper was presented to a dog simultaneously with its food for a sufficiently long period, the presentation of the tone or paper alone finally caused the same flow of saliva that the food had originally evoked. The irrelevant stimulus was named a _food sign_, and the involuntary motor response of salivary secretion was called a _conditioned reflex_ to differentiate it from the similar response to the biologically adequate stimulus of food, which was termed an _unconditioned reflex_. "The significance of the conditioned reflex is simply this, that an associated stimulus brings about a reaction; and this associated stimulus may be from any receptor organ of the body; and it may be formed of course not merely in the laboratory by specially devised experiments, but by association in the ordinary environment."[1] Thus it is evident that the formation of conditioned reflexes takes place in all fields of animal and human activity.