



THE RELATIONS OF SMELL, TASTE, AND THE COMMON 



CHEMICAL SENSE IN VERTEBRATES. 



By George Howard Parker, Sc.D 



1. Introduction. 



For some time past the term chemical sense has been applied as a general 

 term to those senses in which the stimulus is due to the chemical action of environ- 

 mental substances on the nerve terminals of the given sense organs. In man the 

 chemical sense is well represented by taste and smell, but in addition to these, 

 there is also an allied sense whose receptors occur on the exposed or partly 

 exposed mucous surfaces, such as those of the nasal chambers, the cavity of the 

 mouth, the moist surfaces of the eyelids, etc. The receptors on these surfaces 

 are normally stimulated by the chemical action of the material in direct contact 

 with them and they represent collectively a sense as distinct and well denned 

 as smell or taste. This sense has been called by some recent workers the chemical 

 sense or the undifferentiated chemical sense, but, for reasons that will appear 

 later, I shall designate it as the common chemical sense and I shall use the term 

 chemical sense as a generic term, including under it smell, taste, and the sense 

 just alluded to. It is the purpose of this paper to discuss the relations of these 

 three chemical senses in vertebrates, particularly that of the common chemical 



se to taste. 



In studying the chemical senses in vertebrates, my interest 



directed 



especially to the common chemical sense for the reason that very little attention 

 had been paid to it. For a long time investigators have known that the skin of 

 a frog is very susceptible to chemical stimulation and the relation of this stimu- 

 lation to acids, salts, etc., has been investigated by Braeuning (1904) and more 

 recently by Cole (1910) . The results of this work show some striking similarities 

 between this form of stimulation and that of taste, and suggest at once that 

 these two senses are nearly related. To ascertain something of this relation, 

 studies on the stimulation of the skin of certain fresh-water fishes were under- 

 taken and a brief preliminary statement of the work on the catfish, Amiurus 

 nebulosus, was published by me in 1908. A year later Sheldon's extensive study 

 of the common chemical sense of the dogfish appeared. Meanwhile I had carried 

 out somewhat similar work on Ammoccetes, an account of which will be taken 

 up at once. 



2. The Common Chemical Sense 



AMMOC03TES 



The Ammoccetes upon which the following observations were made were 

 obtained through the kindness of Professor S. H. Gage from Lake Cayuga, New 



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