Now these points, where my eyes divined the cryptogam pushing back the soil with its button-like heads, these points, where the ordinary fungoid odour was certainly very pronounced, were never selected by the dog.

He passed them disdainfully, without a sniff, without a stroke of the paw.
Yet the fungi were underground, and their odour was similar to that I have already referred to.
I came back from my outings with the conviction that the truffle-finding nose has some better guide than odour such as we with our sense-organs conceive it.

It must perceive effluvia of another order as well; entirely mysterious to us, and therefore not utilised.

Light has its dark rays--rays without effect upon our retinas, but not apparently on all.

Why should not the domain of smell have its secret emanations, unknown to our senses and perceptible to a different sense-organ?
If the scent of the dog leaves us perplexed in the sense that we cannot possibly say precisely, cannot even suspect what it is that the dog perceives, at least it is clear that it would be erroneous to refer everything to human standards.