REACTIONS OF FISHES TO SALTS 251 



overcome by the salt, though they remained in the salt end dur- 

 ing a majority of the 15 minutes that they were in the tank. 



h. Potassium nitrate. The fishes were consistently negative 

 to this salt in O.OIN concentration. Of 40 fishes tried in the 

 gradient, 27 gave decidedly negative reactions, 5 stayed in the 

 middle third of the tank, and 7 were more or less positive. In 

 only 3 experiments was the time spent in the salt half of the tank, 

 over 60 per cent of the total time. Of the 27 negative fishes, 

 20 spent over 80 per ceht of the time in the tap water end. 



c. Sodium nitrate. Experiments with all three kinds of water 

 were run. In the neutral water the fishes were decidedly nega- 

 tive the graphs showing that 86 per cent of the time was spent 

 in the tap water end of the tank. In the moderately acid water, 

 70 per cent of the reactions were negative and 30 per cent 

 positive. In the strongly acid water, the fishes were decidedly 

 positive to the O.OIN concentration showing an 81 per cent posi- 

 tive reaction. The concentration of the salt was now decreased 

 to 0.002N and the same fishes tried. They were not so positive 

 to this small concentration in the acid water as they had been 

 to the O.OIN solution but they were still more positive than in 

 the moderately acid water. The graphs show 45 per cent of the 

 time was spent in the salt third of the tank, 30 per cent in the 

 middle third, and 25 per cent in the tap water third. These 

 results show again the effect upon the behavior of the fishes, of 

 the antagonistic reaction between the acid and the salt; they 

 select the higher concentration of salt in the gradient in strongly 

 acid water but are negative to this same concentration in water 

 which is not so acid. Note also (table 1, p. 256) that the antago- 

 nism .between the salts and the acid seems to be more marked in 

 the case of the K salts. Table 1 shows that in the case of both 

 the chloride and nitrate of potassium the antagonism between 

 the salt and the acid was sufficient to cause the fishes to react 

 positively in moderately acid water. With sodium, the chlo- 

 ride shows a positive reaction in the moderately acid water but 

 in this same water, the nitrate gives a negative reaction. It is 

 not until the water has been made strongly acid that the fishes 

 react positively to the nitrate of sodium. 



