The growth of organs and structures so remote from the sex-organs, as, e.g., the larynx, have been found to be influenced by the chemical stimulus of secretions from the sex-organs and their subsidiary glands. These secretions are not passed out through external ducts but enter the blood system _directly_. Such secretions passing straight from the ductless glands into the vascular system are of very great importance in almost all our bodily functions. They have recently been much studied, and the general name of _Hormones_ given to them by Starling.[7] The idea that some particular secretions or "humours" are connected with each of the internal organs of the body, is a very ancient one; but we have even yet only the vaguest and most elementary knowledge of a few of the many miracles performed by these subtle chemical substances. Thus we know that the stimulus of food in the stomach sends a chemical substance from one ductless gland in the digestive system chasing through the blood to another gland which prepares a different digestive secretion further on. We know that the thyroid gland in the neck swells and contracts in very sensitive relation with the sex organs; we know that some chemical secretion from the developing embryo, or the tissue in which it grows, sends its chemical stimulus to the distant mammary glands of the mother; we know that if the ovaries of a girl or the testes of a boy are completely cut out, the far-reaching influences their hormones would have exerted are made evident by the numerous changes in the system and departures from the normal, which result from their lack. [7] See Prof. Ernest H. Starling's Croonian Lecture to the Royal Society, 1905. But we do _not_ know, for physiologists have not yet studied the degree and character of the immense stimulus of sex-life and experience on the glands of the sex-organs, or how they affect the whole of the human being's life and powers. The "Mendelians" and the "Mutationists," who both tend to lay so much (and I think such undue) stress on morphological hereditary factors, seem at present to have the ear of the public more than the physiologists. But it is most important that every grown up man and woman should know that through the various chemical substances or "messengers" (which Starling called the hormones) there is an extremely rapid, almost immediate, effect on the activities of organs in remote parts of the body, due to the influences exerted on one or other internal organ. It is therefore clear that any influences exerted on such profoundly important organs as those connected with sex must have far-reaching results in many unexpected fields. What must be taking place in the female system as a result of the completed sex act?