Until comparatively recent times the interest of students of physiology in the inorganic constituents of the body or the so-called mineral nutrients was limited to a few elements. The list comprised sulphur and phosphorus (which exist partly in organic combinations), chlorine, sodium, potassium, calcium, magnesium and iron. This by no means exhausts the variety of elements that can be detected in the body or in the animal and plant products that serve as food; but the others are present in quantities that were described as "traces" and were assumed to represent chance contaminants. Plants, on which ultimately all animal forms depend for sustenance, grow in a medium—the soil— that contains a larger number of elements. It might be expected, therefore, that traces of many of them would inevitably find their way adventitiously into the animal organism, without representing any real essential of life. The discovery, in 1895, of the significant
IS MANGANESE AN ESSENTIAL ELEMENT? JAMA. 1931;97(15):1078–1079. doi:10.1001/jama.1931.02730150034014
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