RESPIRATION IN AIR 81 



noted for the crocodile by Dill and Edwards (1931), but 

 first clearly realized by Irving (1935, 1938). This makes it 

 possible for the diving animal to keep its breath. There is a 

 very interesting difference in behaviour, as pointed out by 

 Irving and noted already by Bohr in the diving birds, which 

 perhaps we should call psychic. If a terrestrial mammal is 

 forcibly submerged it will struggle violently and exhaust itself, 

 while a diver will keep quiet so as to use the least amount of 

 oxygen. This is not, however, of essential significance, be- 

 cause it can be shown that while the divers carry a store of 

 oxygen it is certainly inadequate to supply their normal needs 

 during a diving period. 



The store of oxygen carried by divers is not to any large 

 extent carried in the lungs. Seals frequently, perhaps nor- 

 mally, make an expiration before diving, and Scholander has 

 recently shown that in whales who dive after an inspiration 

 the lungs are small in relation to the size of the body. It 

 would seem that the air in the lungs may be used mainly to 

 regulate buoyancy and, as we shall see later, there are good 

 reasons why it would be fatal to deep divers to have a large 

 volume of air in the lungs. 



The oxygen is carried in a large blood volume and a high 

 concentration of haemoglobin in the blood, and in addition 

 many divers, especially the seals and whales, have large stores 

 of muscle haemoglobin which are presumably oxygen-satu- 

 rated when they make a dive. 



Scholander made up the following balance sheet for a seal 

 (Cystophora) of 29 kg. 



Table 9 



350 ml alveolar air with 16% 2 50 ml 2 



4500 ml blood with 25 vol % 2 1100 " " 



6000 g muscle with 4.5 vol % 2 270 



a a 



Other tissues and fluids 100 



u a 



Total 1520 ml 2 



With the oxygen consumption normally observed such a 

 store might last for five minutes. 



