To purchase this aim, we first need to determine accurately the smallest dose of effective and well tolerated inhaled morphine, to provide the "bolus" dose we have to repeat by titration, which is still currently unknown. This dose is called ED50, it's the effective dose for at least 50% of healthy volunteers relieved. ED50 for intravenous morphine is also needed to be established, unknown in this indication. The determination of these two parallel ED50 would allow a reliable conversion factor between the two routes of administration for morphine "bolus", which can then be tested in comparative titrations. To validate our induced pain model in healthy volunteers, we also have chosen to fix in these conditions the ED50 of fentanyl that the effective dose by nebulization is better known. This study would also describe the pharmacokinetics of inhaled morphine and its derivatives after a single spray.