THE HORMONES IN HUMAN REPRODUCTION 



reach the various organs and tissues which each of them is 

 respectively destined to affect. The hormone of the thyroid, 

 for instance, influences the utilization of oxygen by the tis- 

 sues ; the pancreatic hormone (insulin) regulates the com- 

 bustion of sugar ; adrenin affects the blood pressure by caus- 

 ing the arteries to contract. Just how each ductless gland 

 produces its own special secretion, and why certain particu- 

 lar tissues, and these only, respond to a given hormone, are 

 questions which must be solved by the physiologists and the 

 chemists of the future. 



The ovaries and the testes are also glands of internal secre- 

 tion, or to put the case more precisely, they include such 

 glandular tissue among their complicated make-up. The hor- 

 mones made in the sex glands perform the function of linking 

 the action of the various organs of the genital system, timing 

 and regulating their activities. What these hormones are, 

 where they are produced, and how they act to accomplish the 

 bodily tasks of human reproduction, is the theme of this 

 book. 



One more item should be added to the list of reproductive 

 activities cited above. This is the sexual urge, the totality of 

 impulses that serve to bring the sexes together for mating. 

 It is the most important coordination of all, for without the 

 union of the sexes all the other intricate processes are useless. 

 It, too, is partly regulated by the hormones, but we know too 

 little about this as yet to discuss it profitably here. The way 

 of an eagle in the air, the way of a man with a maid . . . are 

 still in part beyond the reach of science. In view of the fact 

 that we are still ignorant of the means by which the simplest 

 one-celled animal is impelled to conjugate with another of 

 its kind, we can only wonder at the complexity of sex psy- 

 chology in the higher animals, and at all the lures that nature 

 has provided to insure the union of the sexes. What marvels 

 of color and fragrance, bird song and firefly radiance, have 

 been lavished to this end! and for mankind what emotions 



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