THE OSMOTIC RELATIONS BETWEEN FISHES AND 

 THEIR SURROUNDING MEDIUM (PRELIMI- 

 NARY NOTE). 1 



FRANCIS B. SUMNER. 



The effects upon fishes of changes in the density and salinity 

 of the surrounding medium involve numerous problems of great 

 physiological importance. Why is an extreme change of density 

 so fatal in some cases and so harmless in others ? And is it the 

 change of density which is responsible for the harmful effects 

 after all ? May not salt water be toxic in a narrower sense to 

 fresh-water fishes and vice versa? In any case, what is the im- 

 mediate cause of death ? Are the limiting membranes of a fish 

 permeable to both water and salts, or are they only semi-perme- 

 able ? Or are they perhaps impermeable to both ? And are all 

 of the limiting membranes alike in this regard ? Likewise is 

 their condition the same for all species and under all circum- 

 stances ? These are closely related questions. They have re- 

 ceived many and quite contradictory answers. It is hoped that 

 the experiments here discussed have contributed something toward 

 their solution. 



The first of these experiments were chiefly concerned in deter- 

 mining whether a given change in water density was harmful to 

 a given species of fish, records being kept of the rate of death. 

 In a second series, weight determinations were made with a view 

 to ascertaining whether such changes in the density of the sur- 

 rounding medium were accompanied by appreciable osmotic 

 effects upon the fishes. Third, it was sought to discover whether 

 the membranes were permeable to water only or to salts as well. 

 The passage of salts from the fishes into the surrounding water 

 was tested chemically, and likewise the salt content of the tissues 

 of fishes of several species under different conditions was deter- 

 mined. Finally a series of experiments was performed with a 

 view to discovering whether such osmotic changes were confined 



1 A more complete account of these experiments is in course of publication by the 

 Bureau of Fisheries and will, before long, appear in the Bulletin of that bureau. 



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