FUNDULUS AND THE SURROUNDING MEDIUM. 



in weight and after a longer time. This rather sudden death of 

 these in solution "D" accompanied by a smaller loss in weight 

 as compared with the others suggests that in these hypertonic 

 experiments death may be due to the direct action of the excessive 

 amount of sodium chloride present in solution. Still there are 

 evidences of the ability of the organism to react against even this 

 condition for in one experiment in which the fishes were kept in 

 a solution of sea water to which 16 gms. of sea salt were added 

 per liter, most of the specimens were dead after two days showing 

 a loss in weight. One (no. 3) lived for nearly five days and 

 showed in its weight determinations fluctuations similar to the 

 survivors in fresh water although of course in this case they were 

 of an opposite nature due to the hypertonic solution. Mather, 

 '8 1, suggested that the cause of death of salt-water fishes in fresh 

 water was not due so much to chemical differences as to differ- 

 ences in osmotic pressures. Sumner takes the opposite view. 

 But both may play a part in producing the results. It is possible 

 that Fundulus resembles the eel, Anguilla, and undergoes a reduc- 

 tion of the osmotic pressure of its blood after sojourn in fresh 

 water. Dakin, '08, found that in sea water the blood of Anguilla 

 resembled that of marine teleosts, though not quite as great. In 

 fresh water, the osmotic pressure of its blood was similar, though 

 not quite as low as that of the blood of fresh-water teleosts. 



Sumner found that a loss of salts took place when Fundulus is 

 placed in fresh water and that the amount lost decreased as the 

 time of sojourn in fresh water increased. This result also 

 indicates that a decrease in the permeability of the limiting 

 membranes of the body takes place due to the change in the 

 environment. 



At least two positions can be taken with regard to this matter. 

 In the first place however the question arises as to the part of 

 the body concerned in the effects noted. Sumner gives experi- 

 mental evidence based on studies with teleosts to the effect that 

 the gill membranes are the structures concerned. Experiments 

 of my own with elasmobranchs show the same results. With 

 regard to the two possible views to take, one is, that the kidneys 

 regulate the osmotic pressure of the blood when the organism is 

 immersed in fresh water, eliminating the excess of water taken 



