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 
