Cases of the reverse order are equally familiar, in which a taste originally unpleasant comes, with repetition, to lose its disagreeable character, or even to become distinctly pleasing. Indeed, in many such cases habituation results in the establishment of a craving for the quality which was originally repulsive. Here the repetition of the taste quality seems to set up defensive adjustments and adaptations of a profound organic kind rather than the earlier protective reactions of refusal and rejection. Once this adjustment or adaptation takes place the presence of the original stimulus is called for as part of the new condition of balance, and the craving, or appetite, results. In this account, it must be confessed, we speak in terms of vague generalities, since it is not easy to state the precise nature of these biological adaptations. But their existence in the case of many users of such things as olives, garlic, tobacco, liquors, and various drugs is a matter of common experience. _The Early Development of Taste_ In the chapter on “The Evolution of Taste” it will be shown that very early in the development of the forms of animal life there is present a form of sensibility to that type of stimulation which, in our own experience, provokes sensations of taste. The “chemical” sense is thus seen to be a very primitive mode, and adjustments to chemical factors in the environment are present at a very low level of organic development. It is a general rule that capacities which appear thus early in the animal series (phylogeny) also appear relatively early and relatively complete in the development of the individual (ontogeny) of more elaborate forms. So far as we are able to discover, this rule holds for the development of the sense of taste. In a number of cases individual infants have been carefully observed in order to note the order of development of the various senses and the adjustments to stimuli in these different modes. In several cases large numbers of newborn infants have been tested immediately after birth, with the same questions in mind. These studies show that not only is sensibility to taste present at the time of birth, but that the newborn infant reacts in different ways to the various taste qualities. On the first experimental application of taste stimuli distinguishable reactions, such as quiet sucking, grimacing, nausea movements, facial expressions, and varied mimetic behavior, indicate that at least in a rudimentary way the various taste qualities are responded to in a selective or discriminative manner.