CHAPTER XII 



SMELL AND TASTE 



IN Man the chief function of these senses is to guard the 

 entrances to the respiratory and digestive tracts. In this they 

 are not conspicuously efficient, since various poisonous gases, 

 salts, and powders, escape their vigilance. Merely a selection of 

 the substances which occur in air and in food are recognized 

 as having odour or flavour. Smell and taste are only partially 

 distinguished in ordinary parlance. No odorous substance is 

 spoken of as tasteless when taken into the mouth. Its vola- 

 tile constituents, escaping to the chambers of the nose, are said 

 to afford a certain flavour. On the other hand, it is recognized 

 that substances which stimulate the tongue alone bitters, 

 acids, sweets, and salts, unmixed with volatile bodies have no 

 odour. 



Biassed as we necessarily are by the paltry role assigned to 

 smell in our mental life, it seems a little unworthy of the present 

 functions of the great brain that it should have developed 

 in association with the nose. Yet smell and taste are the oldest 

 of the senses. Their origin goes back to the days of chemio- 

 taxis, when the organism, having no specialized sense-organs, 

 was attracted to its mate or to its food, and repelled from con- 

 ditions unsuitable for its well-being, by particles in solution 

 acting as chemical stimulants. An amoeba is chemiotacti- 

 cally drawn towards its food, one spore of an alga is attracted 

 to another, by the particles of matter which drift across the 

 interval between them. 



In the life of many animals smell plays as important a part 

 as that of either of the other senses. One has but to watch a 

 dog " looking " for its master, already full in view, with its 

 nose, to realize that smell is the sense on which a dog chiefly 



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