144 HUMAN PHYSIOLOGY 



anything which is at all bitter is doubly so when it 

 passes over the root at the moment of swallowing. 

 The acid appreciation is more nearly uniform in different 

 places. 



It has been proved that taste, or a sense closely akin 

 to it, is mediated by receptors in the skin of certain 

 fishes. A bit of food held near, but not touching the 

 skin of a catfish, far back toward the tail, may cause the 

 animal to whirl about and seize the morsel. In view 

 of the fact that taste is a sense wrought upon by matters 

 in solution it is not surprising that an animal living in 

 a liquid medium should have this sense represented 

 upon other surfaces than that of the mouth cavity. 



Smell. When we pass from taste to smell we recog- 

 nize that we have taken an important step. Taste, 

 like the sensations which can be evoked through the 

 receptors of the skin, requires the actual contact of the 

 stimulating substance. This may be true of smell also 

 in the sense that portions of the odorous material must 

 be brought to the nerve-endings high in the nose, but 

 our reference or projection in this case is to distant 

 sources of the radiation. When one stands at the edge 

 of a pond and enjoys the fragrance of the waterlilies 

 one does not think that some portion of the flowers is 

 in the nose. On the other hand, when a crystal of salt 

 is tasted one does not refer the sensation to the contents 

 of the box from which the sample has been taken. The 

 difference in the mental attitude is very interesting. 



Endeavors to classify odors have not been particularly 

 successful. The number of types seems large, and 

 different judges can hardly agree as to the distinctions. 

 In fact it is much more difficult to establish an ordered 

 system in the realm of smell than it is has been for any 

 of the other senses. In discussing sound we have the 

 standard of pitch and in describing visual sensations 

 we have the spectrum. Odors, however, do not readily 

 fall into any such continuous series. 



Man is said to be deficient in the acuteness of the 



