Fig. 1. Bioelements and the periodic system. Bioelements invariably or fre- 

 quently present in living organisms are indicated by a continuous arc; those which 

 occur variably and rarely by a broken circle. The numbers indicate the order of 

 their relative percentage. The elements of the Hthosphere, hydrosphere, and 

 atmosphere are also indicated by a continuous, broken, or dotted line. The ele- 

 ments occurring in meteorites are shown by a dot. The numbers indicate their 

 relative abundance. This chart of the periodic system divides the elements into 

 non-metals, light metals, and heavy metals. Missing elements are those of atomic 

 numbers 43, 61, 75, 85, and 87, while Po = polonium, Ac = actinium, and Bv = 

 brevium are radioactive substances, of which so far no long lived isotope is known. 

 (See Hackh, I. W. D., Am. J. Sc, 1918, xlvi, 481; /. Ajn. Chem. Soc, 1908, xl, 

 1023.) 



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