ODORS AND LIFE. 201 
a bath of juice of strawberries and raspberries, used to be 
gently rubbed with sponges saturated with perfumed milk. 
Napoleon I. every morning poured eau-de-Cologne, with 
his own hands, over his head and shoulders. 
IV. 
Above all these questions which we have just skimmed, 
there rises another, of a graver and more mysterious kind, 
one which occurs at the end of all studies that treat of 
sensation, and with regard to which some reflections will 
not be out of place here. To what, outside of us, do those 
sensations which we experience within us correspond ? 
What relation is there between the real world and that im- 
age of the world shadowed in our soul? In the special case 
we are concerned with, what is it in these substances which 
is the cause why they affect our sense of smell? It seems 
certain, in the first place, that odor in itself, so far as it is 
odor, is a mere figment of our mind. Contemporaneous 
physiology proves that excitement of the nerves of sensa- 
tion is followed, in each one, by the sensation that corre- 
sponds with each. When we electrify the eye, we call up 
‘in it an appearance of light; when we electrify the tongue, 
we produce in it a sensation of taste; when we electrify 
the inside of the ear, we provoke in it the effect of a sound. 
So, too, a similar excitement, electric or otherwise, of the 
_ olfactory nerves, creates in our mind the sensation of smell, 
even though no odorous molecule takes part in the phenom- 
enon. Sensation, therefore, seems to depend chiefly on 
the nature of the sensitive nerve. The external world 
seems to contribute to it only by setting in motion the 
nerve-fibres. Even this condition of an impulse infringing 
from without is not indispensable, since in sleep, and in 
madness, we experience sensations of smell which, by the 
testimony of our other senses, answer to no external agent. 
Still, we believe that we can distinguish cases of hallucina- 
