. Human physiology. th, so that it may be easily absorbed. We must also remember that there is no sensation without thebrain—that we do not taste a substance till the irritation of thesensory fibres has been transmitted through these fibres to thebrain. Many of the sensations which we call taste or flavour are not simple butvery complex, in which both smell and touch play a very important is so closely associated with the sense of taste that the odour of a sub- TONGUE AND TASTE—NOSE AND SMELL 199 stance frequently suggests the taste, and the taste sometimes suggests theodour. When t
. Human physiology. th, so that it may be easily absorbed. We must also remember that there is no sensation without thebrain—that we do not taste a substance till the irritation of thesensory fibres has been transmitted through these fibres to thebrain. Many of the sensations which we call taste or flavour are not simple butvery complex, in which both smell and touch play a very important is so closely associated with the sense of taste that the odour of a sub- TONGUE AND TASTE—NOSE AND SMELL 199 stance frequently suggests the taste, and the taste sometimes suggests theodour. When the sense of smell is temporarily destroyed during a severe cold,taste is often partially or entirely lost until the sense of smell returns. Thisexplains also the common practice of holding the nose while taking a dose ofnauseous physic. The organ of smell is the mucous membrane which lines thesurfaces of the ethmoid bone, this portion only of the nasal cavitiesbeing supplied by filaments of the olfactory Fig. 182.—Nerves of the Outer Wall of the Left Nasal Cavity. During ordinary breathing through the nose, the air passesgently through the lower and wider portions of the nasal cavities,without disturbing to any great extent the air which is enclosedby the scroll-like folds of the turbinated bones. Consequently,even though the air may contain particles of odorous matter, fewor none of them come into contact with the terminations of theolfactory nerve, and little or no sensation of smell is we wish to perceive an odour more distinctly, we sniffthe air. In doing this we close the mouth so as to direct thewhole of the inspired air through the nose ; and then draw in theair by repeated short and sudden inspirations. This causes up-ward and abrupt rushes into the nasal cavities, the effect of whichis to disturb the comparatively still air of the olfactory part of thenose, and to exchange some of it for the air containing the odoroussubstance. As soon a
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