100 SECRETS OF ANIMAL LIFE 



a foreign body, and the same is true of the general 

 chemical sense, best known in fishes, which has its 

 seat on various parts of the skin and detects diffus- 

 ing substances. 



It has been widely assumed that the general 

 chemical sense represents the primitive irritability 

 from which smell and taste have been evolved, 

 but the work of Professor G. H. Parker points 

 rather to the conclusion that " the most primitive of 

 the chemical sense organs in the vertebrate is the ol- 

 factory organ, followed by that of the common 

 chemical sense, from which the final organ in the 

 series, the organ of taste, arose." It is certain 

 that the olfactory nerve-cell, characteristic of back- 

 boned animals, such as is pleasantly stimulated 

 when we detect from far inland the tang of the sea, 

 closely resembles that of many humble backboneless 

 animals, such as is stimulated when the sea-anemone 

 in the aquarium stretches its tentacles towards the 

 food which we have dropped in at a distant corner. 

 There is no telling why the stimulation produced 

 in us when we tread on the wild thyme is so very 

 pleasant and why that produced by the corn-spurrey 

 is so very unpleasant, the one flower is just as 

 beautiful as the other; but it is possible that careful 

 inquiry might carry us beyond the bare facts. 

 Certain scents have a stimulating effect on the pulse, 

 increasing our feeling of vitality, and similar scents 

 which have no such physiological virtue may by 

 association acquire vicarious merit. Similarly, 

 some unpleasant natural odors, like that of hound's 



