An anesthetic cartridge is adapted to receive a volume of buffer by displacing a plunger in one end of the anesthetic cartridge inwardly so that addition of the buffer volume will not displace the plunger excessively beyond the end of the cartridge body. The inwardly displaced end is protected by a plug or cover which prevents contamination and which is ejected when the buffer is added. The amount of buffer volume injected is selected to raise the pH of the anesthetic to a target value and to simultaneously achieve a target tonicity.
