From cases in which the cure for the disease is identical with its cause it is but a short step to remedies similar to or in some way associated with the ailment. It seems obvious to Pliny that stone in the bladder can be broken by the herb on which grow what look exactly like pearls. “In the case of no other herb is it so evident for what medicine it is intended; its species is such that it can be recognized at once by sight without book knowledge.”[377] Similarly _ophites_, a marble with serpentine streaks, is used as an amulet against snake-bite.[378] Mithridates discovered that the blood of Pontic ducks should be mixed in antidotes because they live on poison.[379] Heliotrope seed looks like a scorpion’s tail; if scorpions are touched with a sprig of heliotrope they die, and they will not enter ground which has been circumscribed by it.[380] To accelerate a woman’s delivery her lover should take off his belt and gird her with it, then untie it, saying that he has bound her and will unloose her, and then he should go away.[381] An epileptic may be cured by driving an iron nail into the spot where his head rested when he fell in the fit.[382] [Sidenote: The principle of association.] Other instances of association are when the remedy employed is some part of an animal who is free from the disease in question or marked by an opposite state of health. Goats and gazelles never have ophthalmia, hence various portions of their bodies are prescribed for eye diseases.[383] Eagles can gaze at the sun, therefore their gall is efficacious in eye-salves.[384] The bird called ossifrage has a single intestine which digests anything; the end of this intestine serves as an amulet against colic, and indigestion may be cured by merely holding the crop of the bird in one hand.[385] But do not hold it too long or your flesh will waste away. The virus of mares is an ingredient in a candle which makes heads of horses seem to appear when it burns;[386] while ink of the _sepia_ is used in a candle which causes Ethiopians to be seen when it is lighted.[387] These magic candles are borrowed by Pliny from the works of Anaxilaus, and we shall find them a feature of medieval collections of experiments. Earth from a cart-wheel rut is thought a remedy against the bite of the shrew-mouse because that creature is too torpid to cross such a rut;[388] and Pliny believes that none of the virtues attributed to moles by the magicians is more probable than that they are an antidote to the bite of the shrew-mouse, which shuns even ruts, whereas moles burrow freely through the soil.[389] Pliny finds incredible the assertion made by some that a ship will move more slowly if it has the right foot of a tortoise aboard,[390] but the logic of the magic seems evident enough. [Sidenote: Magic transfer of disease.]