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24 We may say, then, that the most unsatisfactory features of Zwaardemaker's method are (1) the adhesion-error, and (2) a tendency which the subject, if he manipulates the odorous cylinder, has toward judging in terms of hand-movement. This difficulty will be discussed in another place.

White the intensity of the stimulus depends in the case of any sense upon the condition of the peripheral organ, no sense-organ is so likely to vary either through obstruction or through exhaustion as is the organ of smell. Let us now consider the variations from the normal condition to which this organ is most subject.

Section 3. Anosmia and Hyperosmia.

Whether pathotogical or non-pathological in origin, anosmia is of three sorts,—respiratory, essential or toxic, and nervous. Respiratory anosmia is due to obstruction of the nasal passages, from asymmetry of the nasal skeleton, from hyperaemia of the respiratory or Schneiderian membrane, or from accumulation of mucus. Toxic anosmia may be due to poisons in the inspired air,—a form not yet investigated,—to injurious fluids introduced directly into the chamber containing the sense-epithelium (as in Aronsohn’s experiments), to poisons, such as morphine, pulverized and blown into the nose, or to certain forms of blood-poisoning, such as chronic nicotine-poisoning. The anosmia of smokers cannot be wholly attributed to their catarrh, though a light, acute nicotine-poisoning does not seem to produce a loss of smell. Nervous anosmia may be congenital,—-i.e., due to imperfect development of the olfactory vesicle in the brain,—or may be senile,—due to degeneration of some of the nervous elements which condition the sense,—or may be due to exhaustion of the olfactory nerve, or to dryness of the epithelium. If we rule out exhaustion,we may say that respiratory anosmia is vastly more common than toxic or nervous. The more peripheral parts of every sense-organ are more subject to injury and disease. Thus, the muscles and lenses of the eye give much more trouble than the retina and the optic nerve. In the case of smell, the sensory epithelium is well protected by its secluded position.

As to hyperaemia of the respiratory mucous membrane, its blood supply is controlled much more by the exigencies of breathing than by those of smell. It is largely under the sway of local reflexes. The fibers of the trigeminus which ramify through it.are closely connected with fibers of the sympathetic nervous system. Too profuse secretion of mucus is the most common mechanical hindrance to smell. On the other hand,