RESPIRATION I33 



However, we have still not answered the question of how these animals, 

 using half the amount of air that we do, bulk for bulk, can yet stay 

 submerged 5-15 times longer than most terrestrial mammals, even 

 allowing for the fact that they can derive twice as much oxygen from the 

 air. The answer is simply that the lungs are not the only parts of the body 

 in which oxygen reserves can be stored. If we take a few deep breaths 

 before diving, some of the oxygen combines with the haemoglobin in our 

 blood and some with the myoglobin in our muscles, while further small 

 quantities are stored in other tissues. Of the total quantity of oxygen 

 which a human diver takes down with him 34 per cent is found in the 

 lungs, 41 per cent in the blood, 13 per cent in the muscle and 12 per cent 

 in other tissues. In diving whales, these proportions are quite different: 

 their smaller lungs contain only 9 per cent, their blood 41 per cent and 

 their tissues 9 per cent, while 41 per cent of the oxygen is found in the 

 muscles. In other words their smaller lung capacity is compensated for 

 by the enormous oxygen-storing properties of their myoglobin (muscle 

 haemoglobin) . Moreover, the proportion of myoglobin in their muscles 

 is far greater than that of terrestrial mammals. Tawara (1951) found that 

 Sei Whales had twice as much and Sperm Whales eight to nine times the 

 amount of myoglobin found in terrestrial mammals. It is, in fact, apparent 

 at first glance that the meat of freshly killed Cetaceans is much darker in 

 colour than beef, and that it is almost black in Sperm Whales and Bottlenose 

 Whales. Since myoglobin is a dark red pigment, this is only to be expected. 



A calculation will show that the amount of oxygen which Fin Whales 

 take down with them is roughly 3,350 litres. You might think that is a 

 good deal, but calculations show that, if we assume that their metabolism, 

 i.e. their rate of combustion, is of the same order as that of terrestrial 

 mammals, it is a quantity of air which would enable them to dive for only 

 half their normal time. Hence, not even the large quantities of myoglobin 

 they have provide an adequate explanation for their long stay under 

 water. We have almost run out of explanations - only one remains : a 

 metabolism that differs radically from that of all terrestrial mammals. 

 In Chapter 1 1 we shall see that while such differences have not been 

 established for the metabolism as a whole, it is quite possible that tempor- 

 ary metabolic changes occur during the process of diving. 



Some authors believe that whales require a minimum of energy while 

 submerged, not only because underwater swimming is easier than swim- 

 ming at the surface, but also because breathing itself takes up energy. 

 However, we now know that only 1-4 per cent of the total metabolism of 

 terrestrial animals is devoted to this purpose, and Irving and Scholander 

 therefore think that, during diving, basic changes in the metabolism must 

 occur particularly in the muscles. 



