Concerning the method by which they
obstruct the procreant function both in men and animals, and in both
sexes, the reader my consult that which has been written already on
the question, Whether devils can through witches turn the minds of
men to love or hatred. There, after the solutions of the arguments, a
specific declaration is made relating to the method by which, with
God's permission, they can obstruct the procreant function.
But it must be noted that such obstruction is caused both intrinsically and extrinsically. Intrinsically they cause it in two ways. First, when they directly prevent the erection of the member which is accomodated to fructification. And this need not seem impossible, when it is considered that they are able to vitiate the natural use of any member. Secondly, when they prevent the flow of the vital essences to the members in which resides the motive force, closing up the seminal ducts so that it does not reach the generative vessels, or so that it cannot be ejaculated, or is fruitlessly spilled.
Extrinsically they cause it at times by means of images, or by the eating of herbs; sometimes by other external means, such as cocks' testicles. But it must not be thought that it is by the virtue of these things that a man is made impotent, but by the occult power of devils' illusions witches by this means procure such impotence, namely, that they cause man to be unable to copulate, or a woman to conceive.
And the reason for this is that God allows them more power over this act, by which the first sin was disseminated, than over other human actions. Similarly they have more power over serpents, which are the most subject to the influence of incantations, than over other animals. Wherefore it has often been found by us and other Inquisitors that they have caused this obstruction by means of serpents or some such things.
For a certain wizard who had been arrested confessed that for many years he had by witchcraft brought sterility upon all the men and animals which inhabited a certain house. Moreover, Nider tells of a wizard named Stadlin who was taken in the diocese of Lausanne, and confessed that in a certain house where a man and his wife were loving, he had by his witchcraft successively killed in the woman's womb seven children, so that for many years the woman always miscarried. And that, in the same way, he had caused that all the pregnant cattle and animals of the house were during those years unable to give birth to any live issue. And when he was questioned as to how he had done this, and what manner of charge should be preferred against him, he discovered his crime, saying: I put a serpent under the threshold of the outer door of the house; and if this is removed, fecundity will be restored to the inhabitants. And it was as he said; for though the serpent was not found, having been reduced to dust, the whole piece of ground was removed, and in the same year fecundity was restored to the wife and to all the animals.
Another instance occurred hardly four years ago in Reichshofen. There was a most notorious witch, who could at all times and by a mere touch bewitch women and cause an abortion. Now the wife of a certain nobleman in that place had become pregnant and had engaged a midwife to take care of her, and had been warned by the midwife not to go out of the castle, and above all to be careful not to hold any speech or conversation with that witch. After some weeks, unmindful of that warning, she went out of the castle to visit some women who were met together on some festive occasion; and when she had sat down for a little, the witch came, and, as if for the purpose of saluting her, placed both her hands on her stomach; and suddenly she felt the child moving in pain. Frightened by this, she returned home and told the midwife what had happened. Then the midwife exclaimed: “Alas! you have already lost your child.” And so it proved when her time came; for she gave birth, not to an entire abortion, but little by little to separate fragments of its head and feet and hands. And the great affliction was permitted by God to punish her husband, whose duty it was to bring witches to justice and avenge their injuries to the Creator.
And there was in the town of Mersburg in the diocese of Constance a certain young man who was bewitched in such a way that he could never perform the carnal act with any woman except one. And many have heard him tell that he had often wished to refuse that woman, and take flight to other lands; but that hitherto he had been compelled to rise up in the night and to come very quickly back, sometimes over land, and sometimes through the air as if he were flying.