The _pia mater_ according to her theory diffuses through this bark by the nerves that substance, moisture, sap, or white chyle which when it flows in its proper course, preserves the human vegetable in a state of well being, but when its course is reverted it becomes the cause of diseases. This nervous fluid, the brain derived principally from the air, which she held to be water in a state of rarefaction, air being the chyle of the upper world, water of the inferior, and the Moon with air and water, as with milk, feeding like a nursing mother, all sublunary creatures, and imparting moisture for their increase, as the Sun imparteth heat and life. Clouds are the milk of the Moon, from which, if she may so express herself, she says it rains air and wind as well as water, wind being air, or rarefied water rarefied still farther. The mutation or rarefaction of water into air takes place by day, the remutation or condensation of air into water by night: this is shown by the dew and by this the ebbing and flowing of the sea are caused. In the brain, as in the root of the animal tree, all diseases, according to Doña Oliva, had their origin. From this theory she deduced a mode of practice, which if it did not facilitate the patient's recovery, was at least not likely to retard it; and tended in no way to counteract, or interfere with the restorative efforts of nature. And although fanciful in its foundation, it was always so humane and generally so reasonable as in a great degree to justify the confidence with which she advanced it. She requested that a board of learned men might be appointed, before whom she might defend her system of philosophy and of therapeutics, and that her practice might be tried for one year, that of Hippocrates and Galen having been tried for two thousand with what effect was daily and miserably seen, when of a thousand persons there were scarcely three who reached the proper termination of life and died by natural decay, the rest being cut off by some violent disease. For, according to her, the natural termination of life is produced by the exhaustion of the radical moisture, which in the course of nature is dried, or consumed, gradually and imperceptibly; death therefore, when that course is not disturbed, being an easy passage to eternity. This gradual desiccation it is which gives to old age the perfection of judgment that distinguishes it; and for the same reason the children of old men are more judicious than others, young men being deficient in judgment by reason of the excess of radical moisture, children still more so.