Lack of self-preservation instinct is usually due to deep-seated psycho-pathologies, too complex to be entered upon here; but we may say in passing that this failure is often due to a division of aims in the subconscious mind, the individual is not sure which self he ought to preserve, and so preserves neither. An excess of self-preservation is often developed in the child who has had a hard struggle to find and express his individuality. The self-preservation instinct has a great influence upon vitality. All observant persons must have noticed how easily the man who has lost his hold upon life, or has given up hope, succumbs to disease. CHAPTER X THE REPRODUCTIVE INSTINCT The reproductive instinct is Nature’s mechanism for ensuring the continuation of the species, and its subjective aspect appears to us as all the emotions and sensations connected with sex. As soon as the demands of the self-preservation instinct are satisfied, as soon as the individual is secure, adequately fed and sufficiently developed, then life tends to overflow the vessel it has filled, and this psychic pressure constitutes sex desire. Sex, however, must not be considered under its physical manifestations only, it has an emotional and mental aspect as well. It is more than the mere overflow of energy in the act of procreation, it is also the desire for the rejuvenation and vital stimulus that is produced by the act of union. Whosoever in considering human problems fails to look beyond the physical stratum of the sex instinct, cannot fail to obtain a false perspective. It has been laid down as a maxim that psychology and physiology ought to be kept strictly separate, but it is impossible to treat adequately of the sex instinct without considering it under both its aspects, for sex activity works in a psycho-physical circle; organic sensations stimulate the emotions, and the emotions react on the organs. A sexual image rising in the mind brings about the preliminary reaction of the physical organs of its expression; and any irritation of the physical organs, however accidental, tends to produce a corresponding emotional state. Stimulus may occur at any point on the psycho-physical circuit, and so may inhibition. The sex instinct forms the nucleus of a huge complex, second only to the group of ideas that centres round the individuality itself. To all ideas and activities that are in any way connected with the gratification of the sexual desire, its energy readily passes over. Dress, the home, the ambitions, each and all may owe their interest to the reproductive instinct which uses them as channels for its fulfilment. CHAPTER XI DEVELOPMENT OF THE REPRODUCTIVE INSTINCT The sex instinct, in the course of development from its infantile aspect to its adult manifestation, goes through well-marked phases which are little known outside the ranks of the psychotherapists, but which are of great importance to the educationalist and sociologist.