The use of the menstrual discharge seems to be to prepare the uterine system for conception. For females do not become pregnant before they commence, nor after they cease having turns; nor while they are suppressed by some disease, by cold or by nursing. Some credible women, however, have said that they become pregnant while nursing, without having had any turn since their last lying-in. It is believed that in these oases they had some discharge, colorless, perhaps, which they did not notice, but which answered the purposes of the common one. Women are not nearly so likely to conceive during the week before a monthly as during the week immediately after.* But although the use of this secretion seems to be to prepare for conception, it is not to be inferred that the reproductive instinct ceases at the "turn of life," or when the woman ceases to menstruate. On the contrary, it is said that this passion often increases at this period, and continues in a greater or less degree to an extreme age. * See, however, Dr. Bull's "Hints to Mothers," pp. 31-58, and 127-129 (published by Longmans, Green & Co.)-- Publishers' note. Conception.--The part performed by the male in the reproduction of the species consists in exciting the organism of the female, and depositing the semen in the vagina. Before I inquire what takes place in the females I propose to speak of the semen. This fluid, which is secreted by the testicles, may be said to possess three kinds of properties, physical, chemical, physiological. Its physical properties are known to every one--it is a thickish, nearly opaque fluid, of a peculiar odor, saltish taste, etc. As to its chemical properties, it is found by analysis to consist of 900 parts of water, 60 of animal muscilage, 10 of soda, 30 of phosphate of lime. Its physiological property is that of exciting the female genital organs in a peculiar manner. When the semen is examined by microscope, there can be distinguished a multitude of small animalculae, which appear to have a rounded head and a long tail. These animalculae move with a certain degree of rapidity. They appear to avoid the light and to delight in the shade. Leeuwenhoek, if not the discoverer of the seminal animalculse, was the first who brought the fact of their existence fully before the public. With respect to their size, he remarked that ten thousand of them might exist in a space not larger than a grain of sand. They have a definite figure, and are obviously different from the animalculse found in any other fluid.* * See Dr. Carpenter's "Animal Physiology," p. 558 (published by H. G. Bonn); Nichol's "Human Physiology," pp. 253-255 (published by Trubner & Co.)--Publishers' note.