102 BULLETIN OF THK BUREAU OF FISHERIES. 



external media." The now rather celebrated utterance of Claude Bernard (186."i. 

 p. 110) is perhaps worth repeating here; I do not recall its having been quoted in an 

 English work: 



In all living beings the internal niediinn, whit-h is a true product of the organi.vn, preserves the 

 necessary relations of exchange and of eiiuilibriuni with the external cosmic nieiliuni, but in proiim- 

 tion as the organism becomes more perfect, the organic medium specializes and isolates itself, in a 

 certain manner, more and more from the surrounding medium. 



The Belgian physiologist, Fredericq, was one of the first to investigate the 

 osmotic relations l)etween the body fluids of marine organisms and the medium in 

 which they live. By the method of dialj'sis, and by determinations of the salinity 

 of the bod}' fluids, he found that in various marine invertebrates these fluids were 

 nearly or (juite isotonic with the sea water. He likewise showed that changes in the 

 .salinity of the water resulted in corresponding changes in the body fluids. As 

 regards fishes (both elasmobranchs and teleosts) Fredericq maintained that the 

 osmotic pressure was considerably less (about one-half) than that of the external 

 medium. 



Bottazzi and his colleagues, working at Naples, employed the cryoscopic method, 

 using Beckmann's apparatus. B3' this method the freezing point of a solution is 

 determined with precision, and from this the osmotic pressure, according to well- 

 known ph^^sical principles. Bottazzi arrived at the same conclusion as Fredericq, 

 relative to the osmotic pressures of the body fluids of marine invertebrates. The 

 reduction in the freezing point (^) due to osmotically active substances in solution 

 was found to be nearly constant, ranging from —2.195° C. to —2.36° C. The mean 

 of all his determinations was —2.29° C, which is the same figure as his mean 

 determination for the local sea water. 



Practically identical results were obtained for elasmobranch fishes, the mean 

 osmotic pressure for the blood of three species being expressed by. z/ = — 2.35t5 C. 

 The difference between these i-esults and those of Fredericq is explained by the fact 

 that the latter inferred a lower osmotic pressure for the blood of elasmobranchs 

 from its lower salt content. The blood is rendered isotonic with sea water, however, 

 by the presence of an unusually large proportion of urea. Tliis correction has been 

 accepted by Fredericq himself. 



For the blood of two species of marine teleosts four determinations by Bottazzi 

 yield the mean figure: ^ = —1.036. The blood of these fishes thus appears to have 

 an osmotic pressure about half that of the water which they inhabit. 



Rodier, Quinton, and Garrey have also determined that the vascular fluids of 

 various marine invertebrates are practically isotonic with the water which they 

 inhabit. Rodier and Garrey, employing the cryoscopic method, have likewise con- 

 firmed the conclusions of Bottazzi regarding the elasmobranchs, while Rodier, Fred 

 ei'icq, and Garrey have by this method obtained confirmatory (though not identical) 

 results for teleosts. 



The mean value of /^ for two elasmobranchs tested by Garrey at "Woods 

 Hole is —1.92°. The mean value for five teleosts is —0.872°, the figures ranging 

 from —0.80° (minuiium for conger eel) to —0.96° (maximum for swordfish). The 

 value of /I for the sea water of the neighborhood was about —1.82°. 



