BREATHING AND GROWTH 107 



is considerably greater than in the stiller depths. 

 The influence of this fact upon the growth of sea- 

 animals is continually brought home to us. Life and 

 foam are old associates. The region of greatest 

 animal growth is just where the water is most sparkling. 

 So long as the swell is not so heavy as to tear and grind 

 all that is not solid rock it will foster growth. ' Full 

 fathom five ' is the depth down to which most 

 corals flourish, sponges cover the rocks, and anemones 

 afforest the coast. Where the tide runs strongest, 

 there will be the richest growth, and that not only be- 

 cause it brings new food with every flood, but because 

 it carries fresh supplies of oxygen. 



The second method that these long-shore encrusting 

 animals adopt to gain more oxygen is to increase 

 their capacity for holding it. The red colour of 

 our blood has exactly that meaning, and as its tone 

 waxes and wanes so does our energy ; and for this 

 reason, that the red pigment has a strong affinity for 

 oxygen, binding it to itself, and in so doing deepening 

 in tone. When rich in oxygen its colour is bright 

 and vitality great ; when poor in oxygen the colour 

 fades and the body grows faint. The sponges and their 

 allies give us a first hint as to the origin of these 

 respiratory pigments, for we find them of the most 

 varied tints, but chiefly red, yellow, and green. These 

 colours which, if we ever notice, we think of merely 

 as decorative effects, possess a value to these animals 

 which decides not life for these tough primeval 

 beings hold to life at many points and defy a sudden 



