106 FROM FISH TO PHILOSOPHER 



data are available: the filtration rate in the former ranges 

 from 120 to 200 cc. per kg. per day; in the latter, the 

 lower (and probably normal) values fall below 12 cc. 

 per kg. per day, a reduction in glomerular activity of 

 ten or more to one. Under these circumstances the glo- 

 meruh become more or less superfluous, and the stage 

 is set for natural selection to favor those mutant forms 

 that have intrinsically the poorest glomeruli, and hence 

 for the evolution of an aglomerular kidney in which 

 urine formation depends entirely on the excretory activ- 

 ity of the renal tubules. And so it has come about that 

 among the permanently established marine teleosts we 

 find all degrees of glomerular degeneration, culminating, 

 in certain famihes, in wholly aglomerular kidneys in 

 which the tubules begin (or end) blindly like a finger 

 cot. 



The discovery of the aglomerular fish kidney by A. Huot 

 in 1897, since confirmed by many investigators, came as 

 a surprise to renal physiologists who had been familiar 

 only with the structure of the nephron in the higher ani- 

 mals, in the fresh-water fishes, and in the Amphibia. The 

 aglomerular fishes were admittedly queer animals out 

 of the sea— first the goosefish or angler, Lophius, then 

 the toadfish, Opsanus, the sea horse. Hippocampus, and 

 the pipefish, Syngnathus— one after another these marine 

 fishes came under investigation to refute the assumption 

 that glomeruli are basically necessary for urine forma- 

 tion, and to demonstrate that the tubules can excrete 

 substances as well as reabsorb them. 



The question of whether tubular excretion was even 

 possible had been a subject of heated controversy in re- 

 nal physiology for nearly a century. At one extreme, 

 some investigators held that the glomerulus is merely a 

 device for regulating the blood flow through the kidney, 

 and that all the important constituents of the mine are 

 excreted by the tubules. At the other extreme were those 

 who contended that all the urinary constituents are sepa- 



