Reighard. — Senses and Learning in Fishes 135 



collected evidence to show that movements of schools of 

 minnows in small inland lakes may be due to slight in- 

 equalities in the temperature of the water. In this con- 

 nection it may be suggested that the temperature of the 

 water may have much to do with directing the move- 

 ments of fishes to their spawning grounds. 



B. The Senses of Taste and Smell are best con- 

 sidered together although the organ of the first is a sur- 

 face receptor, that of the second a distance receptor. 

 Yet both organs serve to make animals aware of chemi- 

 cal differences in substances. 



In man substances must be taken into the mouth in 

 order to be tasted. Liquids and the liquid parts of such 

 things as meat then come into contact with the taste 

 organs while solids reach these organs after being dis- 

 solved by the fluids of the mouth. Whatever we taste is 

 therefore in solution. From these things we get but four 

 sensations of taste, sour, sweet, bitter and salt. So long 

 as we are breathing through the nose the odors of food 

 substances are carried from the back of the mouth by 

 the outgoing breath and so enter the cavity of the nose 

 at the back and affect the organ of smell. We then 

 think that we are merely tasting what is in the mouth 

 and we get the impression that our foods have more taste 

 qualities than sour, salt, bitter and sweet. In reality 

 we both taste and smell the food under these circum- 

 stances. We perceive whatever taste qualities the food 

 may have and at the same time we perceive its odors. 

 The odor sensations thus perceived we call taste sensa- 

 tions and we seem to have many more than four qualities 

 of taste. But if the nose be held so that no breath passes 

 through, it is impossible to smell. We then get but the 

 four taste qualities even though we put into the mouth 

 many substances of very different odors. We thus learn 

 that qualities other than bitter, sweet, sour and salt are 

 perceived by the sense of smell, not by that of taste. 



In order that we may smell a thing, an emanation from 

 it — gas or vapor — must be carried in the air and enter 

 the nose with the breath. At first sight it seems that we 



