||Analysis has shown that eleven elements appear to be approximately constant and predominant in all biological systems. In the human body these constitute 99.9% of the total number of atoms present, but just four of them-carbon, oxygen, hydrogen and nitrogen-correspond to 99% of that total (see table link).The very large percentages of oxygen and hydrogen arise from the high water content of all living systems. Carbon and nitrogen, next in importance, together with oxygen and hydrogen, are the basic elements of organic structures and metabolites of living systems. The other 7 elements, which together represent about 0.9% of the total number of atoms in the human body, are sodium, potassium, calcium, magnesium, phosphorus, sulfur and chlorine. Besides these 11 elements, which are absolutely essential, some ten others, metals and non-metals are required by most biological systems but not necessarily by all biological systems [text from top of page 8]. For ratio of H,O,C and N in E. coli and S. cerevisiae see BNID 101 800, 101 801, respectively.