3 I o WHALES 



comparable Avith those of Cetaceans. The evidence therefore points to the 

 conchision that aquatic mammals in general and Cetaceans in particular 

 have a very high metabolic rate. 



The liver is one of the few Cetacean organs that is regularly processed 

 on factory ships for its yield of vitamin A, which we normally get in butter 

 and other fatty foods and which is an essential part of our diet. Although 

 the quantities of vitamin A found in whales vary from individual to 

 individual (in Blue Whales from i,ooo to 9,000 International Units), the 

 average figures are 4,000 I.U. per gram of liver in Blue Whales, i , 100 I.U. 

 in Fin Whales, and 5,000 I.U. in Sperm Whales. Apart from vitamin A, 

 the liver also contains smaller quantities of the provitamin A, kitol, which 

 is changed into vitamin A by heating. The oil obtained from the blubber, 

 the bones, the flesh and the other organs contains somewhat smaller 

 quantities of vitamin A which, though not lost in the boilers, is destroyed 

 when the fat is hardened, so that it must be put back into margarine. 



The liver of whales contains only negligible quantities of vitamin D. 

 We have seen that no equivalent of cod-liver oil (which contains vitamins 

 A and D) can be obtained from whales. On the other hand, the Cetacean 

 liver contains some constituents of vitamin B complex, roughly to the 

 same extent as the liver of cattle, though the constituent used for counter- 

 acting anaemia has not yet been discovered. Most mammals, man 

 included, can synthesize their own vitamin D when ultra-violet light falls 

 on the ergosterol in their skin. Now, since ultra-violet rays are absorbed by 

 water fairly close to the surface, Cetaceans must obtain all their require- 

 ments of vitamin D from their food and are therefore unable to store large 

 quantities of it in their livers or in other tissues. 



Little is known about the presence or needs of vitamin C in Cetaceans, 

 apart from the fact that traces of it have been found in the adrenal 

 glands, and that the epidermis of the Narwhal contains as much as 

 31 -8 mg. per g. of tissue (cf. p. 55). But we do know that the thorax and 

 the abdomen of Rorquals, porpoises and dolphins occasionally contain a 

 peculiar brown fatty tissue which, though Padoa discussed its presence as 

 early as 1929, has not yet been investigated in detail. Now, a similar 

 brown fatty tissue is commonly found in hedgehogs, hamsters, bats and 

 other hibernating animals, where it is known to be capable of storing 

 large quantities of vitamin C. It is therefore quite possible that this tissue 

 plays a similar role in Cetaceans, particularly in Rorquals which eat little 

 or nothing in winter and which would therefore need large reserves of the 

 vitamin. 



We have seen how Cetaceans maintain their body temperature, and 

 we must now discuss how they cope with the special problems imposed 



