376 



THE AMERICAN NATURALIST [Yol.LVI 



Reactions to Salts in Solution 

 A preliminary series of experiments was run with fish 

 immersed in m/10 solutions of the salts of sea water, 

 made up in fresh water. Kesults were obtained similar 

 to those recorded by Loeb, Thomas and others with fish 

 and corresponding ones known to the writer from experi- 

 ments with the larvse of mosquitoes (1916). 



By using the barrels above the experimental troughs 

 solutions of the salts individually and in combination 

 were introduced into the apparatus, with fresh water or 

 sea water run as the control current. At first tempera- 

 ture and stream pressure were kept constant. The tem- 

 perature averaged 20.5° C. and the pressure was suffi- 

 cient to send the currents horizontally to a distance of 

 six inches from the f-in. glass tubes. 



The reactions to individual salts as compared with 

 fresh water are shown in the table below, only the aver- 

 ages at the end of 25 trials with 10 fish being recorded. 



MgSO, 46 Control, 



CaCl, 6 Control, 20 



MgCl, 5.7 Control, 21.5 



KCl 2 Control, 15 



It is quite evident that with temperature and stream 

 pressure the same, Fundulus heteroclitiis will react quite 

 definitely to salts. It is attracted to the less toxic ones, 

 MgSOi, and NaCl, and is repelled by those that are most 

 toxic to it. 



Similar experiments with sea-water solutions and sea 

 water as the control current brought out quite clearly 

 that for the species used, m/10 solutions of the more 

 toxic individual salts were not strong enough to repel 

 the fish. For example in the case of the most toxic, KCl, 

 the score for 25 trials with 10 fish was 43 for the control 

 sea water and 34 for the experimental current with KCl 

 in m/10 solution. 



Likewise, combinations of the salts showed only too 



