"For myself, I am not only persuaded that without the participation of smell there is no perfect taste, but I am even tempted to believe that smell and taste form only one sense, of which the mouth is the laboratory and the nose the chimney; or, to speak more exactly, that the tongue tastes tactile substances, and the nose gases. This theory may be vigorously defended. "All sapid bodies must be necessarily odorous, which places them as well in the empire of smell as in the empire of taste. "We eat nothing without smelling it with more or less consciousness; and for unknown foods the nose acts always as a sentinel, and cries, 'Who goes there?' "When smell is interrupted, taste is paralysed. This is proved by three experiments, which any one may make successfully: _First_, when the nasal mucous membrane is irritated by a violent cold in the head, taste is entirely obliterated. In anything we swallow there is no taste. The tongue, nevertheless, remains in its normal state. _Second_, if we eat whilst holding tight our nose, we are much astonished to experience the sensation of taste only in an obscure and imperfect manner. By this means the most nauseous medicines are swallowed almost without tasting them. _Third_, we see the same effect if, at the moment we have swallowed, instead of bringing back the tongue to its usual place, we keep it close to the palate. In this case the circulation of the air is intercepted, the organs of smell are not affected, and taste does not occur. These different effects depend upon the same cause, the lack of coöperation of the smell, which makes the sapid body to be appreciated only on account of its juice, and not for the odoriferous gas that emanates from it. "These principles being thus laid down, I regard it as certain that taste gives rise to sensations of three different orders, namely: _direct_ sensation, _complete_ sensation, and _reflex_ sensation. Direct sensation is that first perception which arises from the immediate operation of the organs of the mouth, whilst the appreciable body is yet found on the point of the tongue. Complete sensation is that which is composed of this first perception and of the impression which originates when the food abandons this first position, passes into the back part of the mouth, and impresses the whole organ with both taste and perfume. Reflex sensation is the judgment of the mind upon the impressions transmitted to it by the organ."