These are the main functions of the sexual impulse, and in order to understand any further object of the sexual relationship--or even in order to understand all that is involved in the secondary object of marriage--we must go beyond conscious motives and consider the nature of the sexual impulse, physical and psychic, as rooted in the human organism.
The human organism, as we know, is a machine on which excitations from without, streaming through the nerves and brain, effect internal work, and, notably, stimulate the glandular system.

In recent years the glandular system, and especially that of the ductless glands, has taken on an altogether new significance.

These ductless glands, as we know, liberate into the blood what are termed "hormones," or chemical messengers, which have a complex but precise action in exciting and developing all those physical and psychic activities which make up a full life alike on the general side and the reproductive side, so that their balanced functions are essential to wholesome and complete existence.

In a rudimentary form these functions may be traced back to our earliest ancestors who possessed brains.

In those times the predominant sense for arousing the internal mental and emotional faculties was that of smell, the other senses being gradually evolved subsequently, and it is significant that the pituitary, one of the chief ductless glands active in ourselves to-day, was developed out of the nervous centre for smell in conjunction with the membrane of the mouth.