Homeopathy or homoeopathy is a pseudoscientific system of alternative medicine. It was conceived in 1796 by the German physician Samuel Hahnemann. Its practitioners, called homeopaths, believe that a substance that causes symptoms of a disease in healthy people can cure similar symptoms in sick people; this doctrine is called similia similibus curentur, or "like cures like". Homeopathic preparations are termed remedies and are made using homeopathic dilution. In this process, the selected substance is repeatedly diluted until the final product is chemically indistinguishable from the diluent. Often not even a single molecule of the original substance can be expected to remain in the product. Between each dilution homeopaths may hit and/or shake the product, claiming this makes the diluent remember the original substance after its removal. Practitioners claim that such preparations, upon oral intake, can treat or cure disease.All relevant scientific knowledge about physics, chemistry, biochemistry and biology gained since at least the mid-19th century contradicts homeopathy. Homeopathic remedies are biochemically inert, and have no effect on any known disease. Hahnemann's theory of disease, centered around principles he termed miasms, is inconsistent with subsequent identification of viruses and bacteria as causes of disease.