Sheldon, Reactions to Chemical Stimuli. 287 



water catfisli (Ameiurus), which is quite sensitive to salts. The re- 

 aetious secured by the use of salts are not due to osmosis, as sugar 

 solutions of equal osmotic strength have no effect. 



Reactions to quinine hydrochloride take place oidy in the mouth 

 and spiracles, that is, reactions to quinine take place only on stimu- 

 lation of surfaces hearing taste buds, as Parker found for the cattish. 

 The dogfish is extremely sensitive to picric acid. In strong solution 

 it is extremely distasteful and the aninnd responds vigorously. The 

 response is slow, however, and there are usually premonitory symp- 

 toms before the reaction, as noted for salts. Reactions are also often 

 })rolonged after the stimulus is removed. The mouth and body sur- 

 face are sensitive to n/(30 unquestionably, w^hile an apparent uneasi- 

 ness of the fish seems to indicate that it feels in the mouth, spiracles 

 and nostrils a still greater degree of dilution. Picric acid was used 

 by Parker ('07, '08b) as a bitter stimulus. It was with this idea in 

 mind that the substance was used on the dogfish. It might be argued, 

 nevertheless, that inasmuch as aquatic forms are very sensitive to 

 acid stimuli, the reaction in this case is due to the acid radical in the 

 trinitrophenol rather than to the base which gives to us the bitter 

 taste of picric acid. To test this point neutral ammonium and sodium 

 ])icrates w^ere used. Both of these are as bitter to the human taste as 

 is picric acid. From the tables it will be seen that the fish is by no 

 means as sensitive to these as it is to the picric acid, although weak 

 reactions can be secured by the use of strong solutions. The results 

 show that it can not be assumed that the stimulus of picric acid rests 

 entirely or even largely with the base, but that the acid radical is 

 ])robably responsible almost entirely for its influence on fishes. It 

 is evident, however, that the base does possess a stimulating power, 

 as slight reactions were secured to the neutral ])icrates. It can be 

 stated, therefore, that the dogfish reacts to substances which give us a 

 bitter taste. To stimuli of this character the mouth is more sensitive 

 than is the remainder of the body. On the whole, the fish seems less 

 sensitive to l)itter substances than to the other kinds of stimuli used. 

 Outside of |)i('i'ic acid the animal showed little distaste for the solu- 

 tions used, even ihongli reactions were secured. 



]^o reaction al all could be obtained to sugars. This holds true 



