8a FROM FISH TO PHILOSOPHER 



body weight; the highest figure observed in an estivating 

 fish was 3.1 per cent at the end of 1105 days, but if 

 post-estivation metabolism is included, the maximal fig- 

 ure attainable appears to be closer to 4 per cent. 



In the combustion of protein the sulfur and phos- 

 phorus contained in the protein molecule are normally 

 oxidized to inorganic sulfuric and phosphoric acids and 

 excreted in the urine as neutral salts. Inorganic sulfate 

 accumulates in the estivating lungfish, but phosphate is 

 somehow retained in an organic state so that there is 

 none to be excreted after estivation. There is no accumu- 

 lation of other notable products of metabohsm, no 

 creatine, creatinine, ketone bodies, uric acid, or am- 

 monia. The absence of ammonia is of particular interest, 

 since of all nitrogenous end-products this is one of the 

 most poisonous. Active fish excrete 30 to 70 per cent of 

 their nitrogen as ammonia, almost all the rest appearing 

 as urea, and both are excreted almost entirely by gills; 

 the failure of ammonia to accumulate during estivation 

 conforms with other evidence that the ammonia ex- 

 creted by the active lungfish (and that excreted by other 

 fishes) is not that which is formed in the body by the 

 metabohsm of protein (which is rapidly converted to 

 nontoxic urea by the Hver) but is ammonia that is formed 

 de novo peripherally by the gills or kidneys from some 

 nonprotein precursor. 



Certainly the lungfish, in foin: years of complete anu- 

 ria, sniffers no autointoxication. We estimate that if the 

 animal has a maximal store of fat when it goes into esti- 

 vation, and if it gets the breaks from nature (which 

 knows how to make bricks properly) it might survive for 

 seven years— which, even with an eleven-year rain cycle, 

 is a very long drought. 



When the dormant fish is returned to water the ac- 

 cumulated lurea is excreted in a spectacular maimer 

 through the gills, but not fast enough to prevent its 

 transient osmotic action, so that water is rapidly ab- 



