Homeopathy (also spelled homoeopathy) is a form of alternative medicine in which practitioners treat patients using highly diluted preparations that are believed to cause healthy people to exhibit symptoms that are similar to those exhibited by the patient. The collective weight of scientific evidence has found homeopathy to be no more effective than a placebo.The basic principle of homeopathy, known as the law of similars, is "let like be cured by like". It was first stated by German physician Samuel Hahnemann in 1796. Principles of homeopathy are taken on his word and are not based on the scientific method. Homeopathic “remedies” are prepared by serial dilution with shaking by forceful striking on an elastic body, which homeopaths term succussion. Each dilution followed by succussion is assumed to increase the effectiveness. Homeopaths call this process potentization. Dilution often continues until none of the original substance remains. Apart from the symptoms, homeopaths examine aspects of the patient's physical and psychological state, then homeopathic reference books known as repertories are consulted, and a “remedy” is selected based on the totality of symptoms.