INGO W. D, HACKH 433 



Li, Rb, and Zn, while traces of As, Ce, Co, Cr, Mo, Ni, Pb, Ra, Sr, 

 and Ti, have also been reported in specific instances. These ele- 

 ments are marked by a broken circle in Fig. 1 and are also situated 

 close together, with two exceptions.^ 



This summary would be incomplete without a consideration of the 

 abundance of the elements upon our earth. In Table II the data 

 calculated by Clarke* are systematically arranged and the order of 

 occurrence in the three spheres (gaseous, liquid, and solid) has been 

 embodied in Fig. 1. It is significant that only the four elements C, N, 

 0, and H occur in all three spheres, while only seven, S, CI, K, Na, 

 Mg, Ca, and Fe, are predominant in two spheres. Thus the elements 

 of living matter are also the common elements of the earth surface. 



Plant organisms contain relatively more of the elements of the soil. 

 Titanium seems to be an exception; although it occurs in traces in 

 nearly all plants,^ we know little of its physiological functions. Its 

 abundance in celestial bodies, revealed by the spectrum of titanium 

 oxi^e, would indicate a more important role of this element than is 

 known at present. 



In conclusion, only 5 per cent of the known elements (namely, C, 

 N, O, and H) forms from 96 to 99 per cent of the biosphere,^ while 

 about 15 per cent of the elements is invariably or frequently present, 

 another 20 per cent sometimes occurs in traces in certain organisms, 

 and the remaining 60 per cent of the elements is absent under normal 

 conditions ; thus from 60 to 80 per cent of the elements (absent and 

 rarely encountered) are of a more or less poisonous character. 



^ These two exceptions, Ce and Pb, would indicate that other members of the 

 carbon group, Zr and Sn, should be found in organisms. 



4 Clarke, F. W., U. S. Geol. Survey, Bull. 616, 3rd edition, 1916. 



^ Robinson, W. O., Steinkoenig, L. A., and Miller, C. F., U. S. Dept. Agric, 

 Bureau of Soils, Bull. 600, 1917. 



^ These four elements have also been utilized for a system of structure symbols 

 of organic compounds (see Hackh, I. W. D., Canadian Chem. J., 1918, ii, 135; 

 Science, 1918, xlviii, ZZZ). 



