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Percentages of rats preferring the different unit doses of heroin at day 14. Bold numbers are the sums of the rats of each strain preferring the two lower or the higher unit doses of heroin. Fischer n=11; Lewis n=15. Three Fischer rats and one Lewis rat could not be assigned to any dose because they did not meet the preference criteria.
| Heroin Dose (μg/kg/infusion) | 20 | 50 | Total low doses | 125 | 250 | Total high doses |
|---|---|---|---|---|---|---|
| Fischer (%) | 27 | 78 | 100 | 0 | 0 | 0 |
| Lewis (%) | 0 | 53 | 53 | 47 | 0 | 47 |
