A respiration system feeds an anesthetic gas having, a density ρgas, with a Y-piece for connection to a patient, with a respiration circuit having an inspiration branch and an expiration branch, which extend away from the Y-piece. A first supply line from a branch in the expiration branch leads to an anesthetic gas discharge valve and a second supply line from the branch leads to a reservoir. A too high pressure, opposing expiration, cannot build up in the expiration branch and losses of anesthetic gas are kept to a minimum. A prestressing device exerts a prestressing force onto the valve body of the anesthetic gas discharge valve against the effect of gravity. The mass mvalve and the prestressing force determine a threshold pressure in the anesthetic gas discharge line that results in an opening of the anesthetic gas discharge valve.