184 NATURE AND LIFE. 
into contact with the pituitary membrane. It is the vehi- 
cle, the solvent, of those extremely subtile atoms which, 
acting on the delicate fibres of the nerve, produce in it a 
special movement, which translates itself into the most 
varied sensations. Oxygen, and the existence in that gas 
of a certain proportion of odorous molecules, are the two 
essential conditions of this phenomenon. 
Such is, at least, the result of earlier experiments, and 
of those performed of late years by Nicklés. A curious 
fact, well worthy of attention, is the remarkable diffusibility 
and degree of subdivision exhibited by some odorous sub- 
stances. Ambergris just thrown up on the shore spreads a 
fragrance to a great distance, which guides the seekers 
after that precious substance. Springs of petroleum-oil are 
scented at a very considerable distance. Bartholin affirms 
that the odor of rosemary at sea renders the shores of 
Spain distinguishable long before they are in sight. So, 
too, every one knows that a single grain of musk perfumes 
a room for a whole year, without sensibly losing weight. 
Haller relates that he has kept papers for forty years per- 
fumed by a grain of amber, and that they still retained 
the fragrance at the end of that time. He remarks that 
every inch of their surface had been impregnated by 
sevivsaess Of one grain of amber, and that they had per- 
fumed for 11,600 days a film of air at least a foot in thick- 
ness. Evidently the material quantity of the odorous prin- 
ciple contained in a given volume of such air is so minute 
as to elude imagination. We can readily conceive how 
philosophers cite such instances to give a notion of the 
divisibility of matter. 
In fact, we are now considering matter emitted by 
odorous bodies. This shows that they do not act as cen- 
tres of agitation, occasioning vibrations which pass in 
waves to our organs, to exert on thema purely dynamic 
influence. This giving off of odorous matter, with the ne- 
on 
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