In 1560 a Franciscan monk wrote of Aztecs eating a plant called peyotl “which gives them terrible and ludicrous visions, alleviates hunger and thirst, gives strength and incites to battle.” It was used, he reported “to bring about a state of ecstasy in which one had prophetic visions.” This was the first known reference in literature to the mescal cactus, _Lopophora williamsii_, whose remarkable effects on the human mind ever since have aroused wonderment. Many have experimented with eating the so-called “buttons” of this cactus and have reported all sorts of terrible and ludicrous visions. But no two experimenters apparently have the same experience. After nearly 400 years the supposed active principle, mescaline, has been extracted and the same effects produced either by swallowing or injection of as little as a half gram. First comes a decided nausea which lasts about two hours. This passes and is followed by weird hallucinations. One’s own body seems distorted, with some parts exceedingly small and some very large. A common experience is the feeling that only one’s head is the self. The rest of the body is away somewhere in space. The time sense is badly distorted. Minutes stretch out into hours and days, days and hours are contracted into minutes. There are strange optical delusions—lights flashing before the eyes and floating patches of color. Seldom, however, are actual hallucinatory objects seen. The consumer has the impression that he thinks more clearly than at other times but it has been found that this thought is based more on the sounds than meaning of words. There is a tendency, for example, to argue in puns. An invisible barrier seems to separate one from the rest of the world. This condition lasts for two or three hours, and then passes away, leaving no after affects. The condition has been likened to schizophrenia. Large doses produce catatonic conditions. A person may sit motionless for a long time in an apparently quite uncomfortable position and refuse to move. Dogs and cats given mescaline injections crouch motionless in corners of their cages, only rousing themselves from time to time to attack invisible assailants. It recently has been found that only one chemical constituent of mescaline, beta-phenylethylamine, is responsible for the delusions. This is quite similar in chemical structure to the body hormone adrenaline. There have been conjectures that adrenaline may be changed into the mescaline constituent by some as yet unknown process of body chemistry and that this change may be the physiological cause of schizophrenia. About 40 years ago a peyotl church was set up by Indians in New Mexico. It followed essentially the Catholic ritual, but with mescal buttons substituted for bread in communion. The U.S. Bureau of Indian Affairs did not interfere with the rites when its investigations indicated that the mysterious drug was not habit-forming and apparently caused no physical injury. _The Puzzling Platypus_