discriminator) on the palate:--but when urged by strong appetite as in the act of feeding, and when divested of the restraints which refined society imposes; the nostrils are widely expanded, the eye is keenly directed to the portion, and the hands are busily employed. Experience has sufficiently informed us that the organs of sense must be in a healthy state, in order to the due conveyance of perception. When the function of any organ is altogether defective, as when a person is born blind, he is cut off from all perception of light and of visible objects. If by nature deaf, from the intonation of sounds; and many unhappy instances of such connate defects abound among our species. In one particular subject, both these defects existed from birth; so that the sum of his intelligence was conveyed by the touch, smell, and taste, or in other words, his mind was exclusively composed of the perceptions he derived from these senses. This case will be more particularly noticed in a subsequent chapter. The alterations which take place in the state of our perceptions from a morbid cause, are generally known. Thus a person labouring under a catarrh, will be unable to detect the odours which certain substances communicate in a healthy condition of his olfactory organ. In fever excited by a disordered stomach, the taste will become vitiated, and the partial obstruction of the ear by accumulated wax, will impress him with the bubbling of a pot, the singing of birds, or the ringing of bells. The same law that produces fatigue in a muscle from exertion, appears to obtain in the organs of sense. If they be excited by their appropriate stimuli too violently, or for a too long continuance, fatigue or languor is produced, their percipience is diminished, or confusedly conveyed; and they require a period of rest for their refreshment.