But, it will be said, if man meets so many difficulties in diving, how 

 can the great cetaceans remain beneath the water during half an hour 

 and even more ? How can they reach depths of considerably over a 

 hundred fathoms? How is it that they do not exhibit disturbances 

 similar to those which in man are set up by a lack of oxygen or an 

 excess of nitrogen in the blood? It must be understood to begin 

 with that, the bigger an animal is, the less surface he offers in relation 

 to his weight: if we have to make ten packets of i lb. we shall use, of 

 course, more paper than if we have to make a single packet of lo lb. 

 Hence, the surface area of a large animal is relatively less than that 

 of a small one. Another simile will make it quite clear: lo quarts of hot 

 water distributed in ten pots will get cold much quicker than if they 

 were all in one pot. 



It is then clear that the large cetaceans must produce relatively much 

 less heat than us. Of course, they live in water, which carries off heat 

 better than air: but this fact is more than compensated for by an 

 enormous layer of fat, which is a remarkable insulator. 



These sea giants must then have, in comparison with ourselves, 

 a much slower metabolism : at the same time, with them, each unit of 

 volume must consume less oxygen than with us. Thus they more 

 slowly exhaust the oxygen stored in the red corpuscles of their blood 

 and so carbon dioxide will accumulate more slowly. This is sufficient 

 to explain the length of time they can remain under water. 



Let us note, also, the reverse case : a small mammal like a mole eats 

 every day the equivalent of its own weight. When two rival moles 

 fight, the winner devours the loser without delay. A whale of this 

 voracity is inconceivable. Now the quantity of oxygen absorbed by an 

 animal is necessarily proportional to the quantity of food consumed. 

 We can conclude that the small mammals cannot dive for very long. 



Some other details concerning the cachalot or sperm whale: even 

 if, before he dives, he fills his lungs with air, the volume of this air 

 must diminish during the dive, for the body cannot resist the pressure : 

 at 500 fathoms down, the volume of this air, even if it is not absorbed, 

 is reduced to almost nothing: we must conclude that in the cachalot 

 the bronchiae and trachea are not rigid. 



The cetaceans have, moreover, the peculiarity of being able to 

 adapt themselves to very irregular respiration : the mass of their blood 

 is relatively large. As for explaining why they can go down so deep 

 without feeling the disturbances which man feels, it is very simple: 



[22] 



