ODORS AND LIFE. i 45 



covered with sparkling peai'ls of dew, a fresher and balmier fragrance 

 exhales from every plant. It is the same after a light shower. Vege- 

 tation o-ains heightened tints, at the same time that it diffuses more 

 fragrant waves of perfume. We remark an effect of the same kind in 

 the physiological phenomenon of taste. The saliva serves as an ex- 

 sellent vehicle for diffusing the odorous principles ; then the move- 

 ments of the tongue, spreading that fluid over the whole extent of the 

 cavity of the mouth, and thus enlarging the evaporating surface, are 

 clearly of a kind to aid the dispersion of the odorous principles, which, 

 as we have seen, take a considerable part in the perception of tastes. 



Now, in the phenomenon of smell, air acts in the place of water. 

 It seizes the odorous particles and brings them into contact with the 

 pituitary membrane. It is the vehicle, 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 pro- 

 portion 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 Nickles. A curious fact, well worthy of 

 attention, is the remarkable diffusibility and degree of subdivision 

 exhibited by some odorous substances. 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 

 perfumed by a grain of amber, and that they still retained the fra- 

 grance at the end of that time. He remarks that every inch of their 

 surface had been impregnated by se9io * 64ooo of one grain of amber, 

 and that they had perfumed for 11,600 days a film of air at least a foot 

 in thickness. 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 in- 

 stances 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 centres of agitation, occasioning 

 vibrations which pass in waves to our organs, to exert on them a 

 purely dynamic influence. This giving off of odorous matter, with 

 the necessary aid of oxygen in the atmosphere, proves, too, that odors 

 are in no respect comparable to light or heat, which one may regard 

 in an abstract way, in the immaterial and ethereal space which is the 

 region of their motion, as proper forces, and acting from a distance. 

 Odors, to be perceived, must be taken up by oxygen, and borne by it 



VOL. VI. 10 



