The evolution of metals as essential elements (with special reference to iron and copper).

Abstract

The past few years have witnessed exciting progress in our understanding of the elements required for the growth and survival of the higher animal. As anticipated, these new discoveries have been exclusively among the trace elements, those elements which in minute quantities are essential for growth and development. As shown in Table I, after the discovery of the requirement for cobalt in 1935, there was a hiatus of about two decades before the essentiality of molybdenum (1953), chromium (1957) and selenium (1959) was confirmed. This was the end of an era in trace element research. From here on a major change in the research technique had to be devised. The animals, their food and their entire environment had to undergo a complete trace element decontamination, using special plastic houses, highly purified diets and filtered air. After a decade of painstaking research, Dr. Klaus Schwarz of the Veterans Administration and others added three new elements to the essential list: fluorine, tin and vanadium. In 1972, Dr. Edith Carlisle, University of California, Los Angeles, proved that silicon also was required for the growth and development of chicks. We now know that at least twenty-five of the 96 elements found on earth are required for some form of life (Figure 1; see also Table III).