AQUATIC MAMMALS 



do so. The same may almost be said of mammals which hibernate. 

 This state, apparently, is almost entirely determined by temperature in 

 the case of reptiles, but in mammals this is only partially so, and there 

 seem to be other factors involved. With them metabolism almost ceases, 

 and although the process is not well understood, it must be accomplished 

 in a relatively simple manner, for some species habitually hibernate 

 while other closely related species, in other climates, never do so. 

 Furthermore, some rodents regularly aestivate during the hottest part 

 of the year, when food is scarcest. 



In view of the facts so far available it seems that in any study of 

 the whale's ability to withstand lengthy submergence, account will have 

 to be taken of the possibility that this order, or at least many of its rep- 

 resentatives, may have some apparatus whereby its rate of metabolism 

 is lowered temporarily in a more or less voluntary fashion. So little 

 is yet known of this general subject that there is no way of predicting 

 the probability of this being the case. It may actually be either quite 

 high or zero ; but it should be considered, nevertheless. 



No mention has yet been made of the fact that during deep sub- 

 mergence by a human diver the pressure saturates the blood with nitro- 

 gen, and unless decompression be very gradual, nitrogen bubbles will 

 form in the vascular system, afflicting him with what is known as the 

 "bends" and often causing death. Whales often ascend with rapidity 

 from great depths and at first thought it might seem that they would 

 be obliged to have some provision for overcoming such a disagreeable 

 situation. It must be remembered, however, that a human diver gets 

 a new supply of nitrogen at every breath, while a whale has only the 

 initial supply of this gas which he has taken down with him. Very 

 likely this is not sufficient in amount for saturation of the blood to the 

 point -where the latter would give off bubbles when the animal again 

 reaches the surface. 



Very little is surely known about the depths to which marine mam- 

 mals habitually descend. Almost nothing is known in this regard about 

 pinnipeds. Reports are sufficiently frequent for us to believe that the 

 cachalot often feeds near the bottom where the depth is in excess of 

 a mile. How much deeper it can go is unknown. It is also believed 

 that the other toothed whales of larger size have this ability to a pro- 

 nounced degree. I have been told by a whaler of a finback which was 

 harpooned and at once sounded vertically to the depth of 275 fathoms, 

 where its neck was broken by impact with the bottom, and the carcass 

 was then hauled straight up to the surface. Other reports exceed this 



[320] 



