Materia medica deals with effects rather than primary causes. It seeks to modify the expression, which can only be done through the expressor. It is axiomatic that to change results we deal with causes. This principle is so widely recognized that it is seen in an endless variety of phases, even among barbarous and half-civilized races. The charms and incantations used for healing among Indian tribes have this significance. With all their barbarism they are near to nature and keen in locating causation. With nothing more than a superstitious basis, charms, incantations, dances, images, ceremonies, and shrines have a wonderful influence for healing. They divert the mind from the ailment, and stimulate a strong faith which awakens the recuperative forces to action, and thus cause a rapid recovery. A traveller in Algiers relates the following conversation he had with a Moorish woman of high class: "When ill do you go to the doctor?" he asked. "Oh, no; we go to the Marabout; he writes a few words from the Koran on a piece of paper, which we chew and swallow, with a little water from the sacred well at the Mosque. We need no more and soon recover." If a skilful exercise of baseless superstition upon mind can be so efficacious, what results are possible by a judicious use of the truth? Mental causation is abundantly proved by the well-known effects of fear, anger, envy, anxiety, and other passions and emotions, upon the physical organism. Acute fear will paralyze the nerve centres, and sometimes turn the hair white in a single night. A mother's milk can be poisoned by a fit of anger. An eminent writer, Dr. Tuke, enumerates as among the direct products of fear, insanity, idiocy, paralysis of various muscles and organs, profuse perspiration, cholerina, jaundice, sudden decay of teeth, fatal anaemia, skin diseases, erysipelas, and eczema. Passion, sinful thought, avarice, envy, jealousy, selfishness, all press for external bodily expression. Even false philosophies, false theology, and false conceptions of God make their unwholesome influence felt in every bodily tissue. By infallible law, mental states are mirrored upon the body, but because the process is complex and gradual, we fail to observe the connection. Mind translates itself into flesh and blood.