Both these streams of feeling, it may be noted, sprang from a common source far back in the primitive human world.  All the emanations of the human body, all the spontaneous manifestations of its activities, were mysterious and ominous to early man, pregnant with terror unless met with immense precautions and surrounded by careful ritual.  The manifestations of sex were the least intelligible and the most spontaneous.  Therefore the things of sex were those that most lent themselves to feelings of horror and awe, of impurity and of purity.  They seemed so highly charged with magic potency that there were no things that men more sought to avoid, yet none to which they were impelled to give more thought.  The manifold echoes of that primitive conception of sex, and all the violent reactions that were thus evolved and eventually bound up with the original impulse, compose the streams of tradition that feed our modern world in this matter and determine the ideas of purity that surround us.

At the present day the crude theory of the sexual impulse held on one side, and the ignorant rejection of theory altogether on the other side, are beginning to be seen as both alike unjustified.  We begin to find the grounds for a sounder theory.  Not indeed that the problems of sex, which go so deeply into the whole personal and social life, can ever be settled exclusively upon physiological grounds.  But we have done much to prepare even the loftiest Building of Love when we have attained a clear view of its biological basis.

The progress of chemico-physiological research during recent years has now brought us to new ground for our building.  Indeed the image might well be changed altogether, and it might be said that science has entirely transferred the drama of reproduction to a new stage with new actors.  Therewith the immense emphasis placed on excretion, and the inevitable reaction that emphasis aroused, both alike disappear.  The sexual protagonists are no longer at the surface but within the most secret recesses of the organism, and they appear to science under the name of Hormones or Internal Secretions, always at work within and never themselves condescending to appear at all.  Those products of the sexual glands which in both sexes are cast out of the body, and at an immature stage of knowledge appeared to be excretions, are of primary reproductive importance, but, as regards the sexual constitution of the individual, they are of far less importance than the internal secretions of these very same glands.  It is, however, by no means only the specifically sexual glands which thus exert a sexual influence within the organism.  Other glands in the brain, the throat, and the abdomen,—­such as the thyroid and the adrenals,—­are also elaborating fermentative secretions to throw into the system.  Their mutual play is so elaborate that it is only beginning to be understood.  Some internal secretions stimulate, others inhibit, and the same secretions may under different conditions