Prior drinking of a distinctively flavored fluid lowers the subsequent palatability of that flavor. In a 2-bottle choice situation, preference will shift away from the flavor previously tasted; in a single bottle test, the animal will drink more if 2 equally palatable flavors are alternated than if only one is presented. The effect is relatively short lasting, with recovery occurring within 30 min. It is suggested that this mechanism is an important component in the ability of the animal to self-select an adequate diet from a number of choices, since it would allow for the alternation among nutrients of different palatabilities in the absence of specific deprivations.In the familiar 2-bottle preference test, rats typically demonstrate a greater intake for 1 of the 2 solutions, but rarely, if ever, do they show an all-or-none choice. Preference/aversion functions across concentrations, for example, are typically graded whether increasing or decreasing. Some examples of this are found in experiments by Richter (1939) for sodium chloride, Khavari (1970) for sucrose, Benjamin (1955) for quinine, Hausman (1933) for sodium saccharin, Cullen, Scarborough, and Stager (1970) for calcium saccharin. In all cases the test substance was tested with water.The question can be asked, When given a choice where one solution of the pair appears to be substantially more palatable than the other, why does the animal ingest any of the less palatable solution? Possible explanations in terms of differential postingestional effects that might be used in the sucrose/water or NaCl/water situations become less likely in the saccharin/water case and quite improbable in the quinine/water one. This can be illustrated by reference to some unpublished data (G. R. Morrison, 1972), where 8 rats were given a choice between water and .005% quinine hydrochloride for 2 hr. a day for 26 days. Average daily intake of water was 15.3 ml, of 1
