David Hartley

“ For the sensation, which causes it, disappears the instant before the inspiration; and if this be not strong enough, i.e. if the muscles do not receive the vibrations from the pituitary membrane with sufficient freedom, it returns again and again, being increased by this reciprocation, till at last it causes sneezing. It seems agreeable to this account, that the passage of air, cold absolutely or relatively, through the nose, will often occasion sneezing; and through the mouth, yawning. For cold air must contract the membranes along whose surfaces it passes. ”

“ When sweet smells cause a sudden faintness, and deliquium animi, they may perhaps agitate the whole system of small medullary particles so much, as to make them attract each other with sufficient force to stop all vibratory motions; just as has been observed of the particles of muscular and membranous fibres. And the smells to which a person has an antipathy, may have been originally sweet, or lie so near the confines of pleasure, as to propagate their vibrations much farther than original fœtids can. ”

“ When sneezing rouses from a stupor, it may be supposed to excite the usual degree and kind of vibrations in the medullary substance of the brain, by such a moderate concussion of it, as lies within the limits of nature and health. ”

“ We may add here, that the smell is a guide and guard placed before the taste, as that is before the stomach, in a great degree in men, but much more so in brutes, who have scarce any other means, than that of smell, whereby to distinguish what foods are proper for them. It is likewise probable, that the smell is a guard to the lungs ”

“ And we may observe, that in many other cases also, when the pleasure passes into pain, the automatic motion thereon depending passes into one of an opposite nature; just as in algebra, when an affirmative quantity in the data is changed into a negative one, a like change is to be made sometimes, and yet not always, in the conclusion. ”

“ It deserves notice here, that pinching the nose prevents the perception of these flavours, as it seems, by checking the vibrations, which would run along the pituitary membrane. When the flavours are very pungent, they fix in the tip of the nose; or, if this be hindered by pinching the nose, they fly to the uvula, which is the nearest extreme part to this.
In like manner, pinching the nose, or pressing the lachrymal bag, whose membrane is continuous to the pituitary one, checks the sensation that gives rise to sneezing. ”

“ First, If the varieties of kind in vibrations be combined with those of degree, we shall have a large fund for explaining the various fragrant and fœtid smells, notwithstanding that the first always agree in falling short of the solution of continuity, the last in going beyond it. ”

“ Though odoriferous particles are more subtle than the sapid ones, yet they are perhaps grosser than the rays of light. For the smoke of a tallow candle ceases to smell, when it begins to shine, i.e. when it is more attenuated by heat. Since therefore the vibrations from heat are probably smaller than those from light, we may range the vibrations of the medullary substance in the following order, in respect of subtlety; heat, light, smell, tastes, tangible impressions, and the vibrations of the air, from which sound arises. ”

“ It will be evident, upon a moderate attention, that the grateful smells, with which natural productions abound, have a great share in enlivening many of our ideas, and in the generation of our intellectual pleasures ”