66 THE ORIGIN AND EVOLUTION OF LIFE 



the form of oxyhemoglobin, as a carrier of oxygen from the 

 lungs to the tissues.^ 



Sodium is less important in the nutrition of plant tissues, 

 but 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 phe- 

 nomena through stimulation and inhibition.^ 



Iodine, with its negative ionization, becomes useful through 

 its capacity to unite with hydrogen in the functioning of the 

 brown algae 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 

 experimentation by Loeb, who has shown that its salts induce 

 muscular peristalsis and accelerate the secretory action of the 

 kidneys.^ 



Copper ranks first in electric conductivity. In the inverte- 

 brates, in the form of hemocyanine, it acts as an oxygen carrier 

 in the fluid circulation to the tissues.'^ It is always present in 

 certain molluscs, such as the oyster, and also in the plumage 



^ Henderson, Lawrence J., 1913, p. 241. - Loeb, Jacques, 1906, p. 79. 



^Op. cit., pp. 94, 95. * Henderson, Lawrence J., 1913, p. 242. 



^Op. cit., p. 242. ^Loeb, Jacques, 1906, p. 93. 

 'Henderson, Lawrence J., 1913, p. 241. 



