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Number of trials completed out of 100 possible during morphine tests for individual monkeys, each represented by a different symbol. Data above “Before” indicate the effects of morphine one day after a saline injection (i.e., before MCAM). The horizontal dashed line is at 25 trials; morphine tests were discontinued when a monkey completed fewer than 25 trials. Abscissae: days after administration of 0.32 mg/kg MCAM.
