We have already considered the mind as a tank divided into compartments by sieves of varying diameters of mesh, let us now consider the currents that move in the water that fills the tank. We may diagrammatically conceive the inflow as taking place through one main channel into the subconscious, and there dividing into three streams. This main channel of energy, which supplies the motive power of all living creatures, has been called by many names: libido, horme, élan vitale, and bio-urge; an adequate English equivalent is the thrust of life. This stream of psychic energy becomes specialised in the individual into divergent currents, which we call the three great instincts. The first of these is the SELF-PRESERVATION INSTINCT. Under this heading may be gathered up all the activities which are motived by (1) the Will to Live, or Self-Maintenance, and, (2) the Will to Live more Fully, or Self-Aggrandisement. The second great instinct is that of REPRODUCTION, or SEX, whose function it is to secure race preservation. Through this channel tends to go the surplus of energy left over after the demands of self-maintenance have been fulfilled. The third great instinct is the SOCIAL or HERD INSTINCT, by which term we designate that system of innate tendencies and capacities which enables us to co-operate with our fellows and lead a social life, with all its advantages and disadvantages. Some animals, however, do not have this third instinct, but lead solitary lives, acknowledging no ties save those of mate and offspring; but the more highly evolved types, including man, have developed this great specialisation of psychic energy which enables them to lead a social life. These three great instincts act and react on each other in the hidden field of subconscious, and build up social organisation and individual character. In order to understand the workings of the instincts, however, it must be clearly realised that they are universal and not personal in their scope; the survival or suffering of the unit are not considered in the scheme of things, it is the race that counts. If we regard the instincts as subserving the welfare of the individual only, we form a concept which cannot fail to lead us astray when we seek to put our conclusions to a practical application. The workings of instinct must be viewed from the standpoint of evolutionary progress, not individual well-being. This is the point of view from which Nature frames her schemes, and we can only hope to understand her ways if we occupy her standpoint.