134 WHALES 



Normally, the chemical processes which supply the necessary energy 

 for muscle contractions, can be divided into two phases. In the first 

 (anaerobic) phase the combustible material (glycogen) is broken down 

 in the muscles into lactic acid without the intervention of oxygen, and in 

 the second (aerobic) phase part of this lactic acid is oxidized, while another 

 part is re-synthesized into glycogen. This, at least, is what happens in 

 theory. Now, Irving and Scholander believe that in a nvmiber of animals 

 the anaerobic phase predominates during diving with a consequent saving 

 of oxygen resources. The aerobic phase, however, predominates during 

 surface swimming, when the animals have to take up oxygen with 

 increased intensity. This hypothesis was corroborated by experiments 

 with ducks, rats and seals which showed that dvnüng diving the propor- 

 tion of lactic acid increases considerably in the muscles, but accumulates 

 in the blood shortly after surfacing. From these and other facts which 

 we shall examine more closely in Chapter 5, it has been concluded that 

 during diving the muscles require very little oxygen, and that the blood 

 circulation is switched to the heart and brain instead. Unfortunately, it 

 has not yet been possible to prolong the experimental submersion of 

 Cetaceans sufficiently for a significant amount of lactic acid to accumu- 

 late in the blood. Though direct proof is, therefore, still lacking, it seems 

 probable that the secret of the whales' record diving time rests not only in 

 the oxygen reserve in their muscles, but also in the extremely economical 

 use which they make of their oxygen reserves during diving. 



In other organs, such as the brain, they are probably unable to effect 

 similar economies, and here oxidization is complete, with the consequent 

 formation of carbon dioxide, and increase of the carbonic acid content 

 of the blood. Now we know that in all mammals, man included, such an 

 increase stimulates the medullary respiratory centres. In the case of man, 

 it means that he cannot hold his breath, which, in skin-divers, would be 

 disastrous, and we are therefore not surprised to learn that the Russian 

 biologist, E. Kreps (1941), came to the conclusion that the central nervous 

 system of diving animals is singularly unresponsive to carbonic acid. 



During public discussions of the problem of diving and respiration in 

 whales and dolphins, somebody invariably gets up to ask whether these 

 animals show no signs of caisson sickness - the 'bends'. Whenever men 

 working in diving suits or caissons at great depths are brought to the 

 surface suddenly, they run the risk of paralysis and consequent death. 

 Autopsies will then reveal the presence of bubbles in the heart and in the 

 blood vessels, and particularly in the blood vessels of the lungs. Since these 

 fatal bubbles are generally filled with nitrogen, it is believed that they are 

 due to the fact that air is continuously being pumped into the caisson at 

 the same high pressure as the water outside. At that pressure considerable 



