The effect of zinc toxicity on the calcium, phosphorus, and magnesium content of bone and blood in young rats

Aristotle believed the food of plants and animals to be composed of four "essential elements"--earth, air, fire and water. While our present day concepts of nutrition differ radically from such early beliefs, information in this branch of science is by no means complete. One area where information is lacking is that of the trace elements. Over the last hundred years, and especially in the last thirty years, a steadily increasing number of minerals, occurring in minute amounts in the animal body, have had definite physiological roles assigned to them. Two different kinds of investigations have advanced out understanding of the role of these minerals: (1) the investigation of various naturally occurring diseases of man and animal shown to be due to a dietary deficiency, or excess, of a particular trace element and (2) the investigation of the effects on animals of specially constituted diets, deliberately designed to have an abnormally low, or high, content of the trace mineral under study