Conditioning involved adding one flavor (e.g., vanilla) to an artificial diet of high caloric density and a second flavor (e.g., anise) to a similar low-calorie diet. When the rats were tested with identical foods to which the flavors were added, they showed a strong preference for the high-calorie flavor. The parameters of conditioning were varied in four experiments, which showed that the conditioning of taste preferences is rapid and powerful and has generality over a range of conditioned stimulus parameters. The last experiment indicated that the unconditioned stimulus for this conditioning is probably some oral cue, such as the taste of starch, which is correlated with caloric benefit, rather than caloric benefit per se.

Experiments 1, 2, and 3 demonstrated that 23-day-old rat pups can acquire a conditioned taste preference for a flavor paired with either a more calorically dense diet or a diet that provides more calories than another diet of equal caloric density. Experiment 4 showed that 42-49-day-old rats also can acquire conditioned taste preferences based on differing caloric density and differing caloric outcome. Experiments 5 and 6 demonstrated that adult rats form conditioned taste preferences based only on caloric density. Although these experiments indicate that young rats are apparently capable of more diverse learning than adult rats, the question of what US underlies conditioned taste preferences based on diets of differing caloric density remains unresolved.

Microwave ovens are useful in rapid moisture analysis systems and preliminary drying to prepare analytical samples. Because of uneven heat distribution reported previously, we compared effects of 20 sample locations in a microwave oven cavity on moisture percentages of six meat and three milk samples. The same two hot spots (high moisture percentages) were noted for meat and milk samples. Microwave moisture percentages did not differ from standard oven drying results for meat samples but were higher (P < .05) for milk. Placing the sample beaker consistently in the same microwave oven location is advocated.

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