Smell. 479 



hairs of the ear. The multitude of volatile particles borne through the 

 air constitute, with their chemical affinities, a power of the environment, 

 as able, under proper conditions, to stimulate, and consequently to mod- 

 ify, organic cells, as those other modes of energy we call light and 

 sound. 



As the different tones of vibration have, in the case of the eye and 

 ear, differentiated a separate organ for each tone, so each odorous stim- 

 ulus that is perceived by any pituitary membrane, has so altered some 

 of the cells on that membrane that they are moved and agitated when- 

 ever assailed \)y that particular stimulus, and become more pliant and 

 responsive the oftener the stimulus is applied. There must, therefore, 

 be a separate set of the cells and "rodlike filaments " for every single 

 odor that can be perceived. The number of these is not probably so 

 great as the number of musical tones and noises that can agitate the ear. 

 Many of the odors are compound, and each of the composing elements 

 will seek out the cells and filaments which it is competent to agitate, 

 and these separate agitations, reunited in the brain cells, will form there 

 the compound agitation necessary to a perception of the compound odor, 

 just as the rods and cones of the retina analyze a compound ray of light 

 and restore it again in the optic cells of the brain. It is generally 

 agreed that smell is a sensation arising from chemical reaction between 

 the particles of odorous matter and the mucous fluid of the pituitary 

 membrane. The agitation caused by this union communicates itself to 

 the pituitary organs, and is there arrested as chemical action, but con- 

 tinued along the nerve fibres as nervous electricity. If this chemical 

 action were able to affect all the cells and filaments alike, there could be 

 no discrimination of odors but all would be alike. The reason why they 

 are not all acted upon alike is because the different sorts of chemical 

 action result in the formation of different sorts of molecules on the 

 face of the pituitary gland. This cannot well be otherwise. The 

 following essences all differ in smell, and some of them greatly; viz., 

 Lemon, Bergamot, Neroli, Juniper, Lavender, Cubebs, Pepper and Gilli- 

 flower. It is not possible, therefore, that they all agitate the same cells 

 of smell, yet all these essences are chemically precisely alike, their mole- 

 cules all being composed of ten atoms of carbon and sixteen of 

 hydrogen ( C 10 H 16 ). These compounds are called isomeric, and chem- 

 ists account for their differences by assuming that the molecule of each 

 one has its twenty-six atoms arranged in a different position with regard 

 to each other, and that, therefore, the only difference consists of dif- 

 ferent shaped molecules. 



Oxygen exists in more than one state. In its common state, as it is 

 ordinarily mixed in the air we breath, its molecule is composed of two 

 atoms, and it is odorless, as all know. But electricity may cause some 



