When eaten in quantity, garlic may be strongly evident in the diner's sweat and garlic breath the following day. This is because garlic's strong-smelling sulfur compounds are metabolized, forming allyl methyl sulfide. Allyl methyl sulfide (AMS) cannot be digested and is passed into the blood. It is carried to the lungs and the skin, where it is excreted. Since digestion takes several hours, and release of AMS several hours more, the effect of eating garlic may be present for a long time. The well-known phenomenon of "garlic breath" is allegedly alleviated by eating fresh parsley. The herb is, therefore, included in many garlic recipes, such as "pistou", "persillade", and the garlic butter spread used in garlic bread. Because of the AMS in the bloodstream, it is believed by some to act as a mosquito repellent, but no clinically reported evidence suggests it is actually effective. Abundant sulfur compounds in garlic are also responsible for turning garlic green or blue during pickling and cooking. Under these conditions ("i.e." acidity, heat) the sulfur-containing compound alliin reacts with common amino acids to make pyrroles, clusters of carbon-nitrogen rings. These rings can be linked together into polypyrrole molecules. Ring structures absorb particular wavelengths of light and thus appear colored. The two-pyrrole molecule looks red, the three-pyrrole molecule looks blue, and the four-pyrrole molecule looks green (like chlorophyll, a tetrapyrrole). Like chlorophyll, the pyrrole pigments are safe to eat. Upon cutting, similar to a color change in onion caused by reactions of amino acids with sulfur compounds, garlic can turn green. Numerous cuneiform records show that garlic has been cultivated in Mesopotamia for at least 4,000 years. The use of garlic in China and Egypt also dates back thousands of years. Well-preserved garlic was found in the tomb of Tutankhamun (c. 1325 BC). It was consumed by ancient Greek and Roman soldiers, sailors, and rural classes (Virgil, "Eclogues" ii. 11), and, according to Pliny the Elder ("Natural History" xix. 32), by the African peasantry. Garlic was placed by the ancient Greeks on the piles of stones at crossroads, as a supper for Hecate (Theophrastus, "Characters, The Superstitious Man").