224 SMELL, TASTE, AND CHEMICAL SENSE IN VERTEBRATES. 



lating on the mid-trunk, more so on the tail, and most so at the mouth. No 

 attempts were made in this case to determine which of the two ions was the 

 effective one, but judging from what is known of the salty taste in man (Kahlen- 

 berg, 1898), it is probable that the chlorine ion, and not the sodium ion, was 



the stimulating material 



It is, therefore, not surprising that tests with solutions 



of potas 



chloride should give results indistinguishable from those obtained 



from sodic chloride. 



To a solution of quinine hydrochloride the mid-trunk region of the fish was 



least sensitive, the tail more so, and the mouth very much more so. Thus, though 

 a concentration of m/20 quinine was a minimum stimulus for the tail, the mouth 

 could still be stimulated by a dilution of wi/640. Tnis general sensitiveness of 

 Ammoccetes to bitter substances is in agreement with what Nagel (1894, p. 185) 



found for Sygnathus and Lophius. 



For a sweet stimulus a 2m solution of cane sugar was used. No response 

 could be called forth by this solution from any part of the fish. 



These observations show that the exterior of Ammocoetes can be stimulated 

 by sour, alkaline, salty, and bitter substances, but not by sugar. They also 

 show that to chemical stimuli the mouth is most sensitive, the tail less so, and 



The distribution of this sensitiveness does not agree 



the mid-trunk least so. 

 with that of the sensitiveness to light as already worked out (Parker, 1905), for 

 the fish is most sensitive to light at the posterior end and less so on the trunk and 

 head. This condition favors the view that the integumentary photoreceptors 

 are distinct from those concerned with the common chemical sense. 



3. The Common Chemical Sense of Amiurus. 



Amiurus nebulosus is quite as satisfactory a fish for experimental purposes 

 as Ammoccetes and a series of tests parallel to those carried out on Ammoccetes, 

 were conducted for Amiurus. The results of these tests are summarized in 



Table II. , . 



To solutions of hydrochloric acid, the tail and mid-trunk regions were about 



Similar reactions were 





equally sensitive, but not so sensitive as the mouth. 



obtained from normal solutions of nitric and of sulphuric acids, as well as from 



the less dissociated acetic acid. . , * 



To alkaline solutions, potassic as well as sodic hydrate, the tail and mid-trun 

 regions were equally sensitive, but neither was as sensitive as the moutn. 



The salty solutions of sodic chloride and of potassic chloride were 



indis- 



tinguishable as stimuli, and in these instances as in the others, the mid-trun 

 tail were much alike in their receptive capacity and clearly less sensitive 



the mouth. t e 



To quinine hydrochloride applied to the mid-trunk and tail, no r f*P 



was given, though this reagent proved to be an unexpectedly vig 

 for the mouth. 



orous stimulus 



me moutn. . , x run k 



A 2m solution of cane sugar elicited no response from the tail, the mi 



> 



or even the mouth. 



