In the case of smell it is notorious that odors constantly present soon cease to be observed or even to be observable. Even the most disagreeable and insistent odors fade away in time. In a few minutes stale cheese comes to have no discernible odor, while the odors of tobacco smoke and various perfumes disappear equally quickly. In this sense adaptation seems to be much more like exhaustion or fatigue than in the cases of sound, sight, and pressure, and it may require a considerable interval of freedom from the stimulus before the quality returns. The laws and effects of adaptation are by no means the same for all the senses. Thus, in the case of smell, adaptation to certain odors seems to increase our sensitivity to other odors. In the case of taste the effects are by no means clear nor consistently reported by different observers. In general it seems to be true that the effect of adaptation to a given taste quality has no demonstrable effect on the remaining qualities, and that this effect, as in the case of smell, is of the general character of exhaustion. Taste, along with smell, seems to have not yet developed any peripheral or central mechanism whereby adaptation may take place without actual loss of sensibility. _Acquired Tastes_ In a very different sense the word “adaptation” is often employed to express the phenomenon of habituation in the case of “acquired tastes.” Here the habituation is not to the taste quality, in a sensory sense, but represents a change in the feeling or affective tone which characterizes or accompanies this quality. The easier case to understand is that in which the continued indulgence in a substance, such as ice cream, candy, tobacco, sets up organic effects which have their unpleasant accompaniment. Here it happens that a taste originally very pleasant becomes indifferent or even disgusting. The unpleasantness in such a case is rather easily seen to arise, not from a taste quality alone, but from the total state of the moment. On a later occasion the first appearance of the taste quality may, by well-recognized associative mechanisms, arouse the organic revulsions or memories of them, with the attendant disagreeable effect. The originally agreeable taste then appears to have become disagreeable.