EFFECTS ITPON FISHES OF CHANGES IIST SALINITY OF WATER. 79 



Hgures may indicate a relative average gain, since 4 lots of control fishes, kept 

 in sea water (1.023), together with 6 lots kept in water of density 1.013, and 1 

 in water of density 1.018, all, without exception, showed a loss. It is to be 

 noted that the loss in the l.(»13 water was about the same as that in the full 

 strength sea water. 

 Krperiments 65-68. 



Four sets of experiments with F. <li(ij>lKuiiiK may be brietly sunmiarizetl. 

 The fishes came from Taslunoo Pond, which had, at the time, a density of 1.002, 

 and were kept at the laboratory in running water of the same specific gravit}\ 



In 1 case, in which tliese fishes were transferred to fresh water, the normal 

 loss thi"ough waste is the only change to l)e recorded, but here the diflerence 

 in density was of course slight. 



In 3 cases the fishes were transferred to sea water, a decided loss following 

 in each case, averaging 9.3 per cent in from 12 to 20 houi's. In one of these 

 experiments the fishes, after losing 10 per cent of their weight in 20 hours, 

 were found to gain again. Four of the fishes here used were removed in a 

 dying condition, but the remainder gained 6 per cent during the following day, 

 at the end of which they appeared to be in a perfectly healthy state, and might 

 have lived indefinitely. This is the only case in which the changes during the 

 second day were followed with this species, but the percentage of increase is 

 too great to be accidental. It is, moreover, what would result if two fluids of 

 different osmotic; pressure were sepai'ated by an elastic membrane, permeable 

 to water and (though in less degree) to the salts in .solution. 



In one of the foregoing experiments the fishes, after 12 hours in salt water, 

 were transferred to fresh. There followed a gain of 9 per cent, this being- 

 greater than was the initial loss in this case. This experiment is interesting 

 in comparison with another one (66, <?), in which fishes that had lived for 8 

 days in salt water were ti-ansferred to fresh. No gain whatever resulted. 

 The fishes had reached a new equilibrium, and the normal tension of the 

 membranes had been restored. It is none the less surpi-ising, in view of 

 other experiments, that no endosmotic flow of water here occurred, for, as 

 will be shown later, fishes of this species have a considerably greater salt con- 

 tent after a sojourn of some days in salt water. It might therefore have been 

 expected that they would conduct themselves, in relation to fresh water, just 

 as do the other salt-water species employed in the preceding experiments." 



In 2 cases in which the fishes were transferred from the 1.002 water to 

 water of density 1.013 there was no significant loss, in a third case there was 

 a loss of about 3 per cent in one-half day. 



Transfer from water of the above density to fresh (experiment 60. t) led to 

 no increase. On the contrary, a decrease of over 3 per cent is recorded. 

 In most of these experiments with F. diaphanus, the changes did not appear 

 to result in any harm to the fishes, and can not therefore be regarded as patho- 

 logical. Even when the change was made from the faintly brackish water in which 

 they lived to full strength sea water no deaths had occurred at the time of the second 



<■ In a repetition of this experiment the fishes showed a gain ol 2.5 per cent in one day, but in this case 2 had died. 



