l66 FROM FISH TO PHILOSOPHER 



water, and indeed that they would, if they drank sea 

 water, suffer all the adverse consequences of doing so- 

 excessive salt-loading of the body and dehydration in 

 consequence of both the osmotic diuresis caused by the 

 sodium chloride in the urine and osmotic diarrhea caused 

 by magnesium and sulfate unabsorbed from the intesti- 

 nal tract. Apart from the hazard of diarrhea, the bird 

 kidney can excrete salt in a concentration only about 

 one-half that of sea water, so that drinking sea water 

 would entail the excretion of at least twice as much urine 

 as the volume of sea water ingested. 



Then in 1956 Knut Schmidt-Nielsen and his collabora- 

 tors made one of the most interesting discoveries of mod- 

 em biology when they imdertook the study of the salt 

 and water balance of the double-crested cormorant, 

 Phalacrocorax auritus, at Salisbury Cove. On a diet of 

 fresh fish, of which the birds consumed up to half of 

 their weight per day, the derived water proved to be 

 far more than adequate to cover the excretion of salts 

 and uric acid, and no evidence was obtained that sea 

 water was ever ingested, though this was the only water 

 available except in the food. To determine what would 

 happen if sea water were ingested, quantities amounting 

 to about 6 per cent of the body weight were administered 

 by stomach tube. As was to be expected, the concen- 

 tration and rate of excretion of urine were quickly in- 

 creased, chiefly in relation to increased excretion of so- 

 diimi chloride. But what came as a complete surprise 

 was the secretion of a clear, waterlike liquid by two 

 glands in the head which drain into the internal nares 

 and are known to anatomists as 'nasal glands.' This liq- 

 uid ran from the nasal openings and down the beak to 

 accumulate at the tip from which the drops were shaken 

 off by sudden jerks of the head. The secretion proved 

 to be an almost pure solution of sodium chloride (aver- 

 aging, in the case of the cormorant, 529 milliequiva- 

 lents per liter, with some 12 milliequivalents of potas- 

 sium chloride) , the sodium chloride concentration being 



