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CXXVI. Of the sensation of odours. Do the nerves of the first pair 

 alone give to the pituitary membrane, the power of receiving the im- 

 pression of smell, and do the numerous filaments of the fifth pair, merely 

 impart to it the general sensibility belonging to other parts? This ques- 

 tion appears to require an answer in the affirmative. This pituitary 

 membrane, in fact, possesses two modes of sensibility, perfectly distinct, 

 since the one of the two may be almost completely destroyed, and the 

 other considerably increased. Thus, in violent catarrh, the sensibility of 

 the part, as far as relates to the touch, is very acute, since the pituitary 

 membrane is affected with pain, while the patient is insensible to the 

 strongest smells. 



It seems probable, that the olfactory nerves do not extend into the 

 sinuses, and that these improve the sense of smell, merely by retaining, 

 for a longer lapse of time, a considerable mass of air loaded with odori- 

 ferous particles. I have known detergent injections, strongly scented, 

 thrown into the antrum highmorianum by a fistula in the alveolar pro- 

 cesses, produce no sensation of smell. A phial filled with spirituous 

 liquor having been applied to a fistula in the frontal sir. uses, gave no im- 

 pression to the patient. The true seat of the sense of smell is at the most 

 elevated part of the nostrils, which the nose covers over in the form of a 

 capital. There the pituitary membrane is moister, receives into its tissue 

 the numerous filaments of the first pair of nerves, which arising by two 

 roots from the anterior lobe of the brain, and from the fissure which se- 

 parates it from the posterior lobe, passes from the cranium through the 

 openings of the cribriform plate of the ethmoid bone, and terminates 

 forming, by the expansion of its filaments, a kind of parenchymatous tis- 

 sue not easily distinguished from that of the membrane. The olfactory 

 papillae would soon be destroyed by the contact of the atmospherical air, 

 if they were not covered over by the mucus of the nose. The use of this 

 mucus is, not merely to preserve the extremities of the nerves in a sen- 

 tient state, by preventing them from becoming dry, but, likewise, to 

 lessen the too strong impression that would arise from the immediate 

 contact of the odoriferous particles. It perhaps even combines with the 

 odours, and these affect the olfactory organs, only when dissolved in mu- 

 cus, as the food in saliva. 



As the air is the vehicle of odours, these affect the pituitary membrane, 

 only when we inhale it into the nostrils. Hence, when any odour is 

 grateful to us, we take in short and frequent inspirations, that the whole 

 of the air, which is received into the lungs, may pass through the nasal 

 fossse. We, on the contrary, breathe through the mouth, or we suspend 

 respiration altogether, when smells are disagreeable to us. 



The sense of smell, like all the other senses, is readily impressed in 

 children; though the nasal fossae are, in them, much contracted, and 

 though the sinuses are not yet formed. The general increase of sensi- 

 bility, at this period of life, makes up for the imperfect state of the or- 

 ganization; and it is, in this respect, with the nasal fossae, as with the 

 auditory apparatus, of which an important part, the meatus exturnus, is 

 then not completely evolved. The sense of smell is perfected by the loss 

 of some of the other senses; every body, for example, knows the history 

 of the blind man whom that organ enabled to judge of the continence of 

 his daughter: it becomes blunted by the application of strong and pun- 

 gent odours. Thus, snuff changes the quality of the mucus secreted by 



