The wide distribution of copper in living materials has been recognized for some time. Elvehjem and Lindow1 reviewed the older literature with respect to the copper content of plants. The data suggest that copper should be placed in the group of catalytic elements; it is found in greater amounts in more active portions of plants (young shoots, leaves); buds contain more than wood or bark, and its addition to raw peat soil was found to stimulate plant growth. Rose and Bodansky2 reviewed the older literature with respect to the copper content of animal tissue. With improvement of methods for the detection and quantitative estimation of minute amounts of copper, there is much to support the view that this element is a universal constituent of protoplasm; spectroscopic3 and chemical4 analyses indicate its presence in every organ, human and animal. Failure to find it in the past appears