l62 FROM FISH TO PHILOSOPHER 



Amphibia and fishes in which a sensitive functional ad- 

 justment, upward or downward, of the filtration rate is an 

 intrinsic part of the mechanism of maintaining salt and 

 water balance. 



Under the field conditions studied by Adolph and his 

 collaborators, complete cessation of urine formation was 

 not observed; and they found no evidence that renal 

 function is impaired by repeated but tolerable exposure 

 to heat or moderate dehydration, or both. They estimate 

 that, at maximal daily shade temperature of 120°, 110°, 

 90°, 80°, and 70° F., a man with no water available 

 can survive 2, 3, 5, 7, 9, and 10 days, respectively, if he 

 is engaging in no exercise at all. If he is walking at night 

 until exhausted and resting in the shade thereafter, ex- 

 pected survival is reduced to 1, 2, 3, 5, 7, and 7.5 days. 

 These figures are, of course, estimates only, because 

 there are no reliable data on the actual circimastances of 

 death of men under these conditions. 



At the other extreme of water deprivation are those 

 mammals which have made the sea their permanent 

 habitat: the cosmopolitan seals, the sea lions of the Pa- 

 cific, and the walruses, all of which are carnivores and 

 distantly related to the otters; and the whales, porpoises, 

 and dolphins, the ancestry of which is obscure. The 

 herbivorous sea cow, manatee, and dugong, of Ungulate 

 origin, are not strictly marine but live along the coasts 

 and in the rivers. 



The seals and whales diflFer from each other in the 

 fact that the seals come ashore to breed and bear their 

 young, and also to fish and play along the coasts, 

 whereas the whales never come ashore and bear and 

 nurse their young at sea. Little information is available 

 on these marine mammals, but isolated observations on 

 the urine of the rorqual whale (Balaenoptera bore- 

 dis), the blue whale (B. musculus), the sperm whale 

 (Physeter catodon), the humpback whale (Megaptera 

 hoops), the porpoise (Phocaena sp.), and the seal 



