108 SMELL, TASTE, ALLIED SENSES 



to the common chemical sense as contrasted with our 

 sensations of smell, taste, touch, or pain. The curious 

 feeling that comes from vapors that irritate the eyes, 

 nose, or even the mouth has not the remotest relation 

 to touch, smell, or taste and is only distantly suggestive 

 of pain. Pain, however, is easily separated from the 

 common chemical sense by the use of cocaine, and we 

 are, therefore, entirely justified in concluding that the 

 common chemical sense is a true sense with an indepen- 

 dent set of receptors and a sensation quality entirely its 

 own. In the fishes and amphibians it pervades the whole 

 integument but in the reptiles, birds and mammals it is 

 restricted to the partly exposed mucous membranes of the 

 natural apertures, a restriction that doubtless arose as 

 the vertebrate changed from an aquatic to an air-inhabit- 

 ing form. 



5. BIBLIOGRAPHY 



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