PROCEEDINGS 
OF THE 
ROYAL SOCIETY OF EDINBURGH. 
vol. xiv. 1886-87. No. 124. 
Monday, 2nd May 1887. 
Sir DOUGLAS MACLAGAN, Vice-President, in the Chair. 
The following Communications were read : — 
1. The Objective Cause of Sensation. Part III. — The Sense 
of Smell. By Prof. John Berry Hay craft. 
The end-organs of the special senses are all built up on the same 
type. The history of their development from simple ectodermic 
cells suggests that similar agencies have been at work to produce 
them. Both sapid and odorous substances, and indeed all gaseous 
and liquid molecules, are now known to be in constant vibration, 
and this vibration is more or less characteristic of the substance 
examined. 
The above considerations have led me, for the last five years, to 
teach that, in all probability, it will be possible to connect quality 
of taste and smell with the kind of vibrating stimulus, and that it 
will be possible to demonstrate, as has already been done in the case 
of sight and hearing, the truth of this general statement — that 
quality of sensation will depend (the sensorium being in a normal 
condition) upon the kind or character of the vibrating stimulus. 
There is nothing very new in this idea. Without seeking for its 
germs at an earlier period, we find it clearly enunciated by both 
Hobbes and Hartley ; and in more recent times Mr Herbert Spencer 
has lent the weight of his great authority in the same direction. 
But of experimental proof, without which we cannot rest content, 
VOL. XIV. 18/10/87 O 
