As in the case of the concepts constituting the doctrine of the four elements, we have represented here the basic alchemical concepts not only because of their historical significance, but because, as ingredients of a still functional conception of nature, they assume new significance in a science which seeks to develop, though from different starting-points, a similar conception. As will be seen in our further studies, these concepts prove a welcome enrichment of the language in which we must try to express our readings in nature.