REACTIONS OF FROGS TO CHLORIDES 613 



From these statements I deem it not improbable that the in- 

 tensity of the taste sensations of these metals varies from that of 

 lithium, which is weakest, to that of potassium or ammonium, 

 which are strongest, almost exactly as their stimulating effects on 

 these frogs vary. It is evident from Kahlenberg's words that the 

 intensities of effect in the two cases are at least very similar. The 

 solutions required in our experiments are of course much stronger 

 than those necessary to produce taste sensations, but the range 

 seems comparable with that of taste. The question at once 

 suggests itself, Does the frog's skin possess a general chemical 

 sense comparable with the special sense of taste? One naturally 

 assumes that the stimuli which produce these definite reflexes 

 would in normal frogs give rise to some kind of sensation. If this 

 be so, one of two alternatives is apparently open to us. These 

 reflexes correspond to what in the normal frog is a general chem- 

 ical sense akin to taste, or else, with their definitely timed reac- 

 tions, they correspond to different degrees of pain. As a test of 

 the latter question several frogs were treated with a 1 per cent 

 solution of cocaine until irresponsive to superficial pricking and 

 scratching with a needle and to superficial pinching with forceps. 

 They were then dipped as usual into a 3 m. solution of ammonium 

 chloride. Even in those which most quickly succumbedcompletely 

 to the poisoning effect of cocaine, one reaction to the chloride 

 was obtained after complete loss of the pain reactions. Others, 

 not so quickly poisoned, reacted for thirty to forty minutes to 

 repeated dippings into the chloride while the pain reactions were 

 totally absent. If, however, the entire foot was grasped and 

 pinched in the forceps a reaction occurred showing that the deeper 

 nerves were as yet essentially unaffected by the drug. In these tests 

 the superficial stimulation, scratching and pricking, was severe 

 enough to draw blood. It, therefore, seems clear that the reac- 

 tions to the chloride are not pain reflexes. As the frog's skin 

 has been shown to be sensitive to light (Parker, '03), may it not 

 also be sensitive to chemicals in a way more analogous to taste 

 than to any other sense with which we are acquainted or to which 

 we may refer it in comparison? 



THE JOriiXAI. OF COMPARATIVE NEUROLOGY' AND PSYCHOLOGY, VOL.20, NO. 6. 



