different character of the sensory end-organ, the receptor of these vibrations. As Head says : “Each peripheral end-organ is a specific resonator attuned to some particular kind of physical vibration”—reminding us not only of sound-resonators, but also of wireless receivers, which are “tuned” or accommodated to particular wave-lengths.
Thus, if red rays encounter certain tactile end-organs in the skin, they are perceived by the mind as heat, and if they pass into the eye and stimulate the retina, they are perceived as red light. In other words, in whatsoever manner an end-organ is stimulated, it only induces its own particular sensation.
How it comes about that the various end-organs induce such different sensations is not yet known.
The ultra-violet theory of olfaction, however, has to run the gauntlet of much more serious criticism than the difficulty we have just disposed of.
One great objection to it (to my mind) is that it fails to account for another absorption phenomenon of which I have not yet made any mention. It was first observed by Tyndall nearly fifty years ago.
On submitting odorous vapours to examination
