It is this.

There may be a physical reason for the strange connection between the sense of smell and the mind.
The olfactory nerve--so my friend, the Professor, tells me--is the only one directly connected with the hemispheres of the brain, the parts in which, as we have every reason to believe, the intellectual processes are performed.

To speak more truly the olfactory "nerve" is not a nerve at all, he says, but a part of the brain, in intimate connection with its anterior lobes.

Whether this anatomical arrangement is at the bottom of the facts I have mentioned, I will not decide, but it is curious enough to be worth remembering.

Contrast the sense of taste, as a source of suggestive impressions, with that of smell.