ORIGIN OF LIFE UPON THE EARTH 183
u alw contained in one of the phyBiologically important BubatanceB of bile."
Potassiam, separates hydrogen from itB union with oxygen in water, wd is the most active of the metals, biologically considered, in its posi- tive ionization." Throngh stimnlation and inhibition potassium salts piay an important part in the regulation of life phenomena, and they 1% essential to the living tissues of plants and animals, fresh-water and
��marine plants, in particular, storing up large quantities in their tissues.** Potassium is of service to life in building up complex compounds from which the potassium can not be dissociated as a free ion ; it is tbna one of the building stones of living matter."""
Magnesium is fourth in order of activity among the metallic ele- ments. It is essential to the chlorophyll, or green coloring matter of plants, which in the presence of sunshine serves in the dissociation of o^gen from the carbon of carbon dioxide and the hydrogen of water. It is also found in the skeletons of many invertebrates and in the coral- line algte.
Calcium is third in order of activity among the metallic elements. According to Loeb'*^ it plays an important part in the life phenomena through stimulation (irritability) and inhibition. It unites with carbon as carbonate of lime and is contained in many of those animal skeletons which, through deposition, make np an important part of the earth's cmst. In invertebrates the carbonate, except in certain hrachiopods, is
•I GieB, W. J.
» Caesium is more electropoutive.— I*. W. Clarke.
■■ Loeb, Jacques, 1906, p. 04.
tMOp. dt., p. 72.
1*1 Op. nU 1906, F- 94.
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