II50 BTHvLETIN OF THE BUREAU OF FISHERIES. 



lowering of the specific gravity noted above might be interpreted as a reaction 

 of the organism toward the normal condition. The water necessary to dilute 

 the blood could be drawn in from the tissues. 



An experiment was devised to test the relation between temperature and 

 the lowering of the specific gravity of the blood. Three lots of fish were used. 



Lot A. — Sea water at temperature of laboratory, i8° C. 



Lot B.— Fresh water at 27° C. 



Lot C— Fresh water at 7° C. 



The fishes were kept in these solutions from one to six hours. At the end 

 of that period the average specific gravity of blood of — 



Lot A was 1.0506, 18° sea water. 



Lot B was 1.0463, 28° fresh water. 



Lot C was 1 .0501 , 7° fresh water. 



In other words, the cold water had prevented the decrease in specific gravity. 



Now it is known that temperature is an important factor in osmotic ex- 

 changes and also in physiology of circulation. Therefore, whether the more 

 sluggish movement of the blood through the gills is responsible for the difference 

 between B and C or whether the lowering of temperature produced a condition 

 in the gill membrane making osmotic changes more difficult can not be deter- 

 mined at present. We have seen from the previous experiments that if fishes 

 are placed in a more dilute solution the blood is diluted; if placed in a more con- 

 centrated solution the blood is concentrated. It is not believed, however, that 

 in the time during which the fishes were subjected to these various media there 

 was any increased formation of red corpuscles or any destruction of the same. 



Are the phenomena described above purely osmotic, and thus physical in 

 their nature, or is there something more — that is, physiological or vital — con- 

 cerned here? Certainly some of the phenomena observed above lead toward 

 the latter interpretation. The great adaptability of the organism is well shown 

 in the case of the specimen living in fresh water for two months, and again in 

 the case of a few fish which lived for over a month in a solution the concentra- 

 tion of which was increased 50 per cent. It must be remembered that Fundulus 

 heteroclitus is found not only in sea water but also in brackish water and inlets 

 of fresh-water streams. Whether the above changes are true of the teleosts 

 which are strictly marine, I can not say. 



