Water 



61 



land mammals. The urine of marine mammals can be more concentrated than 

 sea water. Recorded freezing points show much variation (see Table 6). 

 The concentration of blood of two marine birds is about the same as that of 

 the mammals CAi=0.64-0.69). -'O-^ These values are to be compared with a 

 blood freezing point of — .58°C. in man. In the seal, Phoca vituline, '>^ no 

 water is lost for temperature regulation, hence the only loss is by lungs, feces, 

 and urine. To saturate the air breathed from the lungs would take 106 gm. 

 water; the feces require 200 gm. water for fish food corresponding to 100 

 calories. When seals are fed herring v\hich are 80 per cent vvater, the amount 

 yielding 100 calories (1250 gm. fish) would contain 1000 gm. water. By 



••dO-r 



+ 40-- 



-60 



■loo 



Fig. 22. Recovery of water load in per cent of initial load after access to water following 

 periods of privation resulting in deficits equivalent to 4 to 8 per cent of bodv weight. From 

 Adolph.' 



oxidative breakdown the fat and protein would \ield 121 gm. of metabolic 

 water. Thus 1121 minus 306 leaves 815 gm. H^.O for the urine. The food 

 (1250 gm. of herring) would yield urea and salt sufficient to give in 800 ml. 

 of urine a freezing point of — 2.7°C. (6.3 per cent urea and 1.4 per cent salt), 

 f^omer Smith --" observed that harbor seals when fasting excrete 0.03-0. 1 1 

 ml./urine/min. with a A., of 1.948, whereas after a meal of herring the rate 

 of excretion increases to 0.08-1.28 ml./min., and the Au rises to 1.98-3.646. 

 The magnesium and chloride of the urine and intestinal residue are so low that 

 it is unlikely that any sea water has been swallowed. Thus marine mammals 

 living on Hsh can get ample water from their food alone to keep their blood 

 more dilute than the ocean. 



