odours are material. They pass through the air as vapours, and they are known to travel miles on the wind. That is to say, apart from those hypothetical varietics of odour (if we can call them odour at all) discussed by Fabre earlier in this book, odours do not emanate from a point and disperse in all directions as light and sound do, Why then drag in the ether? Is it not more probable that the odorous molecule acts on the olfactory hairs by direct material contact, and that it sets up chemical changes in them ?
We are asked to believe that the ultra-violet rays of odour stimulate the olfactory hairs as visible light-rays stimulate the retina, But it must not be forgotten that in the eye those rays may induce first of all chemical changes in the retina, just as they would act on the silver salt of a photographic plate, and that it may be by these changes that the retina is stimulated.
In the phenomenon of olfactory exhaustion, as we said in our first chapter, we have a circumstance which suggests the presence of some chemical reagent in the olfactory area.
It may be, of course, that in the nose as well as in the eye the process is a combination of chemical and physical changes. And in any cage we are here dealing with that obscure region where chemistry and physics meet and mingle.
