The topographical distributions of concanavalin A-binding sites on the surfaces of 3T3, proteasetreated 3T3, and simian virus 40-transformed 3T3 cultured mouse fibroblasts appear to be different, as shown by a shadow-cast replica technique using concanavalin A and a hemocyanin marker, or as shown previously on isolated membranes with concanavalin A coupled to ferritin. However, chemical fixation of cells before labeling with concanavalin A and hemocyanin, or labeling exclusively at 40, allows one to distinguish between inherent concanavalin A-binding-site topography and potential rearrangement of sites induced by the action of the multivalent concanavalin A molecule itself. The inherent distribution of binding sites on 3T3, protease-treated 3T3, and transformed cells is actually the same on all cells, i.e., dispersed and random. Treatment of unfixed transformed or protease-treated 3T3 cells, but not normal 3T3 cells, with concanavalin A and hemocyanin at 370 (or at 40 with subsequent warming to 37°), however, results in clustering of binding sites, presumably due to crosslinking of neighboring lectin-binding sites by the quadrivalent concanavalin A. Thus, the underlying difference between concanavalin A-binding sites on normal as compared with transformed or protease-treated normal cells lies not in the inherent topography of binding sites, but rather in the susceptibility of the sites to aggregation by concanavalin A. The latter may reflect an increased mobility of lectin-binding sites on transformed or protease-treated cells.

Drinking was studied in rats pressing a bar on a second-order schedule in which every third completion of a 1-min fixed interval was followed by food presentation. A brief flash of light signaled the completion of each fixed-interval component. The rats drank not only after the food presentations but also after presentations of the light flash alone. A high rate of steady drinking followed intervals terminated by a food presentation. Drinking that followed intervals terminated by a light flash alone was of comparable rate, but characteristically interrupted by bar pressing. When 250-mg food pellets were used instead of 45-mg pellets, both drinking and bar-pressing rates increased substantially. (Falk, 1961 b) and schedules that differentially reinforce low rates of response (Segal and Holloway, 1963; Segal and Deadwyler, 1965;Segal and Oden, 1965) also engender convincing levels of polydipsia. Furthermore, pellets presented with no specified response dependency involved can also produce the phenomenon (Falk, 1961a;Reynierse, 1966).As Falk (1969) pointed out in his comprehensive review, the determinants of this behavior appear to be complex. Regardless of the schedule employed, however, polydipsia can be elicited from suitably deprived rats by the manipulation of only two variables (Falk, 1966b(Falk, , 1969 time and the amount of food presented produce a characteristic drinking behavior. Once developed, the polydipsia is quite stable, but easily manipulated.In the present experiments, a second-order schedule was employed in which every completion of a 1-min fixed-interval schedule was followed by brief presentation of a stimulus and every third completion of the fixed interval was also followed by presentaion of food. The pattern of drinking that occurred after the presentation of food also came to occur after the presentation of the visual stimulus alone. This result emphasizes the importance of schedule factors in determining polydipsia and allows analyses of the phenomenon not directly related to the usual sequence of drinking following eating. METHOD