that this far-flung summons is addressed to a sense of smell of the same nature as ours. It would be tantamount, he says, “to reddening a lake with an atom of carmine, to filling immensity with nothing.”
It is impossible not to sympathise with this opinion, but caution compels us to say that for the most striking of these observations, that of the calling of the males against a high wind, we should like to have confirmation by some independent observer.
Besides, I think perhaps Fabre would have hesitated to express his scepticism regarding the power of insect olfaction had he known more of the marvels of the human sense.
Vanillin, for example, is perceptible by us as a smell when it amounts to no more than 0'000000005 gram in a litre of air ; and we can perceive mercaptan, a substance with a garlicky odour, in a dilution of 1⁄460,000,000 of a milligram in fifty cubic centimetres of air (approximately 0'0000000026 of a grain in a little over three cubic inches of air !) (See also p. 108.)
What is this but immensity filled with nothing ? And yet we, even we, microsmatic though we are, can perceive that “nothing.”
But we must pick up again the thread of Fabre's argument. Baffled as he feels himself to be when he regards olfaction in the light of these observa-
