When we have inspired a strong and penetrating odour, the sensation is prolonged for a certain time, sometimes for several hours. It is probable that in this case the impression is not single, but is incessantly renewed by the odoriferous particles with which the mucus of the pituitary membrane is impregnated, or which is confined in the air in the sinuses. Sometimes also the odour has penetrated the garments, or is attached to the skin or the hair, and from thence continues its impressions.

Any vigorous exercise, or eating, by exciting the secretions, generally causes the sensation to disappear, the persistence of which might be exceedingly inconvenient.

Gerdy makes the sense of smell the counsellor of the stomach. When the appetite is excited the smell of food is agreeable; but it is repugnant, on the contrary, when hunger is appeased, and the sense of smell warns us to take no more food. We may say, with reason perhaps, that this sense completes that of taste, by enabling us to appreciate the aroma, without which food and drink would cause only a gross sensation, or one at least entirely devoid of all delicacy. When the sense of smell is lost, or even enfeebled, the taste, perceiving flavours only, seems almost extinguished, existing alone.

The sense of smell is very unequally developed in individuals, but it is said to be of extreme delicacy in some races of men, and especially among savages. The stories recounted of individuals following game by tracking, and of negroes who could distinguish by smell the tracks of a negro from those of a white man, seem to indicate a faculty quite as nearly related to the sense of sight as to the one under consideration; and it must be admitted also that individual experience and careful attention to particular circumstances produce the same results when applied to the sense of smell, as to sight or to hearing.