REACTIONS OF FISHES TO SALTS 257 



binations of salts in a gradient, and I present a number of experi- 

 ments of this sort here. They show that fishes recognize and 

 react to combinations of salts according to the prediction which 

 might have been made from the results of previous work upon 

 antagonism. 



It will be remembered that fishes are slightly positive to O.OIN 

 NaNOs in moderately acid water. It was found, however, that 

 they are negative to this salt in water that is but faintly acid 

 and for this reason the following experiments were run in water 

 which contained less than 8 cc. CO2 per liter. The experiments 

 were first run as regular salt experiments such as have been 

 described before, and then the antagonizing salt was added to 

 the salt flow. The concentration of the original salt was always 

 O.OIN and that of the antagonizing salt 0.0002N, i.e., a bare 

 trace was added. The results of these experiments are shown 

 in table 2. A considerable number of experiments was run with 

 each combination in the tap water, and then some check experi- 

 ments were run in distilled water. The results in the distilled 

 water gradients are very similar to those in the tap water. 



Discussion of the experiments with antagonizing salt combinations 



Table 2 shows clearly that the antagonistic action of the salts 

 is detected and reacted to by the fishes. This is shown, for 

 instance, in the sodium nitrate experiments; here the fishes were 

 70 per cent negative to this salt in slightly acid water but when 

 a trace of calcium nitrate was added the negative response fell 

 off to 21 per cent and the positive rose from 30 to 79 per cent. 

 Then in strongly acid water the positive response increased to 

 96 per cent. The reactions of fishes in any gradient are due to 

 their tendency to move about until they reach an environment 

 that neither over- nor under-stimulates them. Thus they will 

 not remain quietly in water that is strongly acid nor will they 

 do so in water that is neutral. A slight degree of acidity (1-6 

 cc. CO2 per liter. Wells '15 a) furnishes their optimum stimula- 

 tion as far as H ion is concerned. The reversal in reaction of 

 the fishes in gradients to which a trace of an antagonistic salt 



