Under certain unusual organic conditions, and also still more commonly in the case of degenerate and neurotic individuals, various perversions of taste occur. These perversions do not seem to be exclusively gustatory in character, since they involve more general factors, such as appetite, craving, and emotional disturbance. The name _parorexia_ is sometimes given to these perversions of taste and appetite. One of the subforms, known as _malacia_, takes the form of an urgent desire for hot spices, or for sour and acid foods, such as pickles. What is known as “salt hunger” is a very similar condition, especially often found among the lower animals. Another form of such perversion, known as _pica_, shows itself in the desire to eat such substances as clay, chalk, and similar gritty or earthy substances. Especially often among children and among certain primitive peoples the chewing of these substances often seems to give a satisfaction quite unfamiliar to the majority of mankind. Little is known about such perversions beyond the fact that they have often been reported. Under certain conditions of mental degeneracy and nervous disorder perversions sometimes arise which have been classed under the term _allotriophagia_. This perversion takes the form of eating with apparent relish various kinds of filth which are commonly offensive and disgusting. In these cases it is quite possible that there is no genuine taste disorder. Many, if, indeed, not most, of our revulsions against substances known as filth arise on the basis of associated circumstances, rather than on the simple basis of their taste qualities. The falling away, or deterioration, of these associative and æsthetic controls in the case of the demented and degenerate, and their absence in the case of the feeble-minded and imbecile, may easily lead to reactions which suggest but do not necessarily involve genuine taste disorder. ------------------------------------------------------------------------ CHAPTER XIII FOOD AND FLAVOR _The Biological Rôle of Taste_