200 THE HAUNTS OF LIFE 



NEW WAYS OF BREATHING 



The colonisation of the dry land by aquatic 

 animals cannot have been an easy task, and 

 our question now is : What were the necessary 

 qualifications ? 



The first qualification was ability to capture 

 the oxygen of the dry air. There is a much 

 larger proportion of oxygen in the air than there 

 is mixed with the water, but it is not so readily 

 available. For, mixed with the water, it seems to 

 seep in very readily through the delicate moist 

 skin of the general surface of the body, or of 

 special organs, such as gills. On one side of the 

 membrane there is water, with oxygen mixed 

 in it ; on the other side of the membrane there 

 is blood, which usually carries a pigment with 

 a strong affinity for oxygen. What happens in 

 aquatic breathing is that the oxygen diffuses 

 through the skin into the blood, usually entering 

 into a loose, chemical union with the blood- 

 pigment. With its captured oxygen the blood 

 passes to the living tissues of the animal, to the 

 muscles, for instance, and there surrenders its 

 oxygen to keep up the ceaseless burning (or 

 oxidation) which living implies. As the result 

 of the combustion (or oxidation) of complex 



