74 HULLKTIN OF THE BUKKAU OF FISHERIES. 



Ill iinother experiment (experiment 81) in which li.shes from (dihited) suit wati r 

 (l.olH) were transferred to fresh, there was a j^ain of 2 per cent durino- tiie tii-st (l:i\ . 

 followed l)V a loss of more tluin L per cent durinjr the sec(jiul. 

 K,-p,rhu,nt J,.'. 



New Yorl>, April, ll»Oo. ^'ine F. lu-ti'i-aditus whieii had been for six dav- 

 in fresh water were put back into the salt water of the aejuarium (1.009). A 

 loss of nearly S per cent occurred duriiiff the first day, after which the weight 

 remained stationar}- for a day." It v.ould thus appear that water of thi~ 

 density was hypertonic to fishes which had li\ed in fresh. 

 Krp,-r!i)u'nf 4-J. 



In this experiment J\ /" t< r^cmux was tiansferred to fresh water. The fishes 

 W(>re throui^'liout weij^'hed indixidually. The results are in au-reement with 

 the fori'goinu-. hut the tigures are not given, since the method of procedure 

 was not so careful, this being the tirst of my experiments in weighing. 

 It seems to me that all of the results thus far tabulated are ii harmony witli the 

 following provisional hypothesis: The body fluids of the fishes used had, at the 

 conmiencement of the experiments, an osmotic pressure lying .somewhere between 

 that of water of densitj' 1.005 and water of density 1.015. Transfer to a medium 

 whicii was decidedly hypertonic resulted in loss of weight; transfer to a medium 

 which was decidedly hypotonic resulted in a gain in weight. In the former case, the 

 osmotic pressure of the fluids of the fishes was raised, in the latter case it was low- 

 ered. In neither case, however, was an osmotic equilibrium between the "internal 

 and external medium" established. The osmotic pressure of the bodv fluids of 

 the fishes fluctuated within a much narrower range than did that of the suri-ounding 

 water. Furthermore, the change in weight bore no constant ratio to the change in 

 the osmotic pressure of the water, as a comparison between the li and the c figures 

 shows. Again, it is evident here and elsewhere that greater changes in weight 

 oci-urred in those cases in which tlie fishes were atiected harmfully l)y the new 

 medium. 



It is only fair, however, that 1 should mention one experiment with /". h.t, ,■"- 

 r//'fus, in which the results are hard to reconcile with the otliers. 

 E.i-p<:rlm,nt U. 



New York, April, 1905. Twenty -five fishes changed from water of densit_> 

 1.010 to water of density 1.018. Not only was there no loss, but apparently a 

 slight gain during the first day, followed by a decrea.se of about liper cent 

 on the second. The accidental dropping of a bit of food into the tank might 

 liave been responsible for the result, though this can not be assumed as an 

 explanation. 

 The experiment in which the scales were remo\ ed prior to the change of medium 

 has alreadj- been discussed (p|). (I'i-ti-):) in reference to the survival of the fishes. An 

 analysis of the changes in weight is here worth while 

 Experiment 1)5 . 



New York, April, 1905. For an account of conditions see page 63. 



" It must t)C rcoordetl here that the 9 fishes were all that survived of a lot of 50, the remainder of which had died from 



