1 84 THE SCIENTIFIC MONTHLY
far more important as skeletal material than the phosphates : the lime- stones form only about five per cent, of the sedimentaries. Shales and sandstones are far more abundant.
Iron is essential for the production of chlorophyll^^* though, un- like magnesium, it is not contained in it. It is present as well in all protoplasm, while in the higher animals it serves, in the form of oxy- hemoglobin, as a carrier of oxygen from the lungs to the tissues.****
Sodium is less important in the nutrition of plant tissues, buti serves an essential function in all animal life in relation to movement through muscular contraction.*®* Its salts, like those of calcium, play an important part in the regulation of life phenomena through stimu- lation and inhibition.*®'
Iodine, with its negative ionization, becomes useful through its capacity to unite with hydrogen in the functioning of the brown algsB and in many other marine organisms. It is also an organic constituent in the thyroid gland of the vertebrates.*®* The iodine content of crinoids — stalked echinoderms — varies widely in organisms gathered from different parts of the ocean according to the temperature and the iodine content of the sea-water. Iodine and bromine are important constituents of the organic axes of gorgonias.
Chlorine, like iodine, a non-metallic element with negative ions, is abundant in marine algae and present in many other plants, while in animals it is present in both blood and lymph. In union with hydrogen as hydrochloric acid it serves a very important function in the gastric digestion of proteins.*®^
Barium, rarely present in plants, has been used in animal experi- mentation by Loeb, who has shown that its salts induce muscular peri- stalsis and accelerate the secretory action of the kidneys.*®*
Copper ranks first in electric conductivity. In the invertebrates, in the form of hemocyanine, it acts as an oxygen carrier in the fluid circula- tion to the tissues,*®® It is always present in certain molluscs, such as the oyster, and also in the plumage of a bird, the Turaco. Although among the rare life elements it ranks first in toxic action upon fungi, alg8B, and in general upon all plants, yet it is occasionally found in the tissues of trees growing in copper-ore regions.**®
In general most of the metallic compounds and several of the non- metallic compounds are toxic or destructive to life when present in large
iw Sachs, Julius, 1882, p. 699.
108 Henderson, Lawrence J., 1913, p. 241.
104 Loeb, Jacques, 1906, p. 79.
105 Op. cit,, pp. 94, 95.
106 Henderson, Lawrence J., 1913, p. 242. lOT Op. cit, p. 242.
108 Loeb, Jacques, 1906, p. 93. '-
109 Henderson, Lawrence J., 1913, p. 241.
110 Howe, M. A., letter of February 24, 1916.
�� �
