Ill] OF OSMOTIC REGULATION 249 



from that of the sea-water outside: but with certain chemical 

 diiferences, for instance that the chlorides within are much 

 diminished, and the molecular concentration is eked out by large 

 accumulations of urea in the blood. The marine teleosts, on the 

 other hand, have a much lower osmotic pressure within than that 

 of the sea-water outside, and only a httle higher than that of their 

 fresh-water allies. Some, hke the conger-eel, maintain an all but 

 constant internal concentration, very different from that outside; 

 and this fish, like others, is constantly absorbing water from the sea ; 

 it must be exuding or excreting salt continually*. Other teleosts 

 differ greatly in their powers of regulation and of tolerance, the 

 common stickleback (which we may come across in a pool or in the 

 middle of the North Sea) being exceptionally tolerant or "eury- 

 halinef." Physiology becomes "comparative" when it deals with 

 differences such as these, and Claude Bernard foresaw the existence 

 of just such differences: "Chez tous les etres vivants le milieu 

 interieur, qui est un produit de I'organisme, conserve les rapports 

 necessaires d'echange avec le milieu exterieur; mais a mesure que 

 I'organisme devient plus parfait le milieu organique se specifie, et 

 s'isole en quel que sorte de plus en plus au milieu ambiant J." Claude 

 Bernard was building, if I mistake not, on Bichat's earUer concept, 

 famous in its day, of life as "une alternation habituelle d'action de 

 la part des corps exterieurs,* et de reaction de la part du corps 

 vivant": out of which grew his still more famous aphorism, "La 

 vie est I'ensemble des fonctions qui resistent a la mort§." 



One crab, like one fish, differs widely from another in its power 



* Probably by help of Henle's tubules in the kidney, which structures the dogfish 

 does not possess. But the gills have their part to play as water-regulators, as 

 also, for instance, in the crab. 



t The grey mullets go down to the sea to spawn, but may live and grow in 

 brackish or nearly fresh- water. The several species differ much in their adaptability, 

 and Brunelli sets forth, as follows, the range of salinity which each can tolerate : 



M. auratus 24-35 per mille 



saliens 16-40 



chelo 10-40 

 capita 5-40 



cephalus 4^0 



X Introduction d Vetude de la medecine experimentale, 1855, p. 110. For a dis- 

 cussion of this famous concept see J. Barcroft, "La fixite du milieu interieur est 

 la condition de la vie libre," Biol. Reviews, viii, pp. 24-87, 1932. 



§ Sur la vie et la mart, p. 1. 



