Democritus says that dreams are formed by the illapse of adventitious representations. Strato, that the irrational part of the soul in sleep becoming more sensible is moved by the rational part of it. Herophilus, that dreams which are caused by divine instinct have a necessary cause; but dreams which have their origin from a natural cause arise from the soul's forming within itself the images of those things which are convenient for it, and which will happen; those dreams which are of a constitution mixed of both these have their origin from the fortuitous appulse of images, as when we see those things which please us; thus it happens many times to those persons who in their sleep imagine they embrace their mistresses. CHAPTER III. OF THE NATURE OF GENERATIVE SEED. Aristotle says, that seed is that thing which contains in itself a power of moving, whereby it is enabled to produce a being like unto that from whence it was emitted. Pythagoras, that seed is the sediment of that which nourisheth us, the froth of the purest blood, of the same nature of the blood and marrow of our bodies. Alcmaeon, that it is part of the brain. Plato, that it is the deflux of the spinal marrow. Epicurus, that it is a fragment torn from the body and soul. Democritus, that it proceeds from all the parts of the body, and chiefly from the principal parts, as the tissues and muscles. CHAPTER IV. WHETHER THE SPERM BE A BODY. Leucippus and Zeno say, that it is a body and a fragment of the soul. Pythagoras, Plato, and Aristotle, that the spermatic faculty is incorporeal, as the mind is which moves the body; but the effused matter is corporeal. Strato and Democritus, that the essential power is a body; for it is like spirit. CHAPTER V. WHETHER WOMEN DO GIVE A SPERMATIC EMISSION AS MEN DO. Pythagoras, Epicurus, and Democritus say, that women have a seminal projection, but their spermatic vessels are inverted; and it is this that makes them have a venereal appetite. Aristotle and Plato, that they emit a material moisture, as sweat we see produced by exercise and labor; but that moisture has no spermatic power. Hippo, that women have a seminal emission, but not after the mode of men; it contributes nothing to generation, for it falls outside of the matrix; and therefore some women without coition, especially widows, give the seed. They also assert that from men the bones, from women the flesh proceed. CHAPTER VI. HOW IT IS THAT CONCEPTIONS ARE MADE. Aristotle says, that conception takes place when the womb is drawn down by the natural purgation, and the monthly terms attract from the whole mass part of the purest blood, and this is met by the seed of man. On the contrary, there is a failure by the impurity and inflation of the womb, by fear and grief, by the weakness of women, or the decline of strength in men. CHAPTER VII. AFTER WHAT MANNER MALES AND FEMALES ARE GENERATED.