902 Proceedings of Royal Society of Edinburgh. [sess. 
as pimento, menthol, and many others, when snuffed also produce a 
sensation in the nostrils quite different from that of their perfume. 
Curiously enough, they all produce a similar sensation, and only 
vary in degree ; and all of them give a sensation similar to that of 
tobacco-snuff, which is more an irritation than a smell. Of course, 
when these substances are applied to the nostrils in the form of 
powders the sensation is compounded of the contact effect of the 
dust and of the perfume ; the latter is probably perceived by 
some part of the surface not affected by the dust. It is probable 
that none of the dust ever comes in contact with the more 
sensitive part of the olfactory surfaces, which are out of reach of 
the direct air-currents. When we consider that all these odorous 
substances in the form of fine powders give rise to almost the same 
sensation, though in varying degrees, the probability is they are 
all perceived by the branch of the fifth nerve, which serves the 
inside of the nostril over which the main air-currents flow, and 
have no effect on the olfactory nerve, on which only gases or vapours 
appear to act. 
(. Issued separately September 30 , 1905 .) 
