The treatment for infertility by Arab medical experts often depends on the type of conception theory they follow. The two-seed theory states that female sexual pleasure needs to be maximized in order to ensure the secretion of more seeds and thus maximize the chances of conception. Ibn Sina recommends that men need to try to enlarge their penises or to narrow the woman's vagina in order to increase the woman's sexual pleasure and thus increase the chance of producing an offspring. Another theory of conception, the "seed and soil" model, states that the sperm is the only gamete and the role of the woman's body is purely for nourishment of the embryo. Treatments used by followers of this method often include treating infertile women with substances that are similar to fertilizer. One example of such a treatment is the insertion of fig juice into the womb. The recipe for fig juice includes substances that have been used as agricultural fertilizer.