1. AN APPARATUS FOR TREATING TOOTH CAVITIES COMPRISING, IN COMBINATION, AN UPPER HEAD PORTION; FIRST CHAMBER MEANS ADAPTED TO CONTAIN A MEDICATED LIQUID TO BE DISCHARGED INTO A TOOTH CAVITY TO BE TREATED; SECOND CHAMBER MEANS ADAPTED TO RECEIVE LIQUID AND EXTRANEOUS MATTER FROM THE TOOTH CAVITY, SAID FIRST AND SECOND CHAMBER MEANS BEING ARRANGED BENEATH SAID UPPER HEAD PORTION, SAID SECOND CHAMBER MEANS ARRANGED BENEATH SAID FIRST CHAMBER MEANS; MEANS CONNECTING SAID SECOND CHAMBER MEANS TO SAID FIRST CHAMBER MEANS; MEANS CONNECTING SAID FIRST CHAMBER MEANS TO SAID UPPER HEAD PORTION; A MAIN DUCT FORMED IN SAID HEAD PORTION AND HAVING AN OPEN END COMMUNICATING WITH ATMOSPHERE; INLET MEANS ADAPTED TO BE CONNECTED TO A SOURCE OF COMPRESSED AIR AND COMMUNICATING WITH THE OTHER END OF SAID MAIN DUCT; FIRST PASSAGE MEANS PROVIDING COMMUNICATION BETWEEN SAID MAIN DUCT AND SAID FIRST CHAMBER MEANS SO THAT COMPRESSED AIR ENTERING SAID MAIN DUCT THROUGH SAID INLET MEANS WILL PASS INTO SAID FIRST CHAMBER MEANS TO PROVIDE PRESSURE ON A LIQUID THEREIN; VENTURI MEANS LOCATED IN SAID MAIN DUCT DOWNSTREAM OF SAID FIRST PASSAGE MEANS AND COMMUNICATING THROUGH SAID OPEN END OF SAID MAIN DUCT WITH THE ATMOSPHERE, SAID VENTURI MEANS FORMING IN SAID HEAD PORTION A SUCTION CHAMBER; SECOND PASSAGE MEANS PROVIDING COMMUNICATION BETWEEN SAID SUCTION CHAMBER AND SAID SECOND CHAMBER MEANS SO AS TO PROVIDE DURING FLOW OF COMPRESSED AIR THROUGH SAID VENTURI MEANS A PARTIAL VACUUM IN SAID SECOND CHAMBER MEANS; FIRST FEED DUCT MEANS HAVING AN UPPER PORTION EXTENDING SUBSTANTIALLY NORMAL TO SAID COMMON AXIS AND BEING FORMED AT LEAST IN PART IN SAID HEAD PORTION AND A LOWER PORTION EXTENDING IN SAID FIRST CHAMBER MEANS BELOW THE LEVEL OF LIQUID THEREIN; SECOND FEED DUCT MEANS HAVING AN UPPER PORTION EXTENDING SUBSTANTIALLY NORMAL TO SAID COMMON AXIS AND BEING FORMED AT LEAST IN PART IN SAID HEAD PORTION AND A LOWER PORTION EXTENDING INTO SAID SECOND CHAMBER MEANS; AND A PAIR OF HOLLOW NEEDLES FLUID-TIGHTLY CONNECTED AT ONE END THEREOF AND CARRIED BY SAID UPPER PORTIONS OF SAID FIRST AND SECOND FEED DUCT MEANS, RESPECTIVELY, SAID FEED DUCTS AND SAID NEEDLS ARE LOCATED ABOVE SAID FIRST CHAMBER MEANS, SAID NEEDLES HAVING FREE ENDS ADAPTED TO BE LOCATED IN THE TOOTH CAVITY TO BE TREATED AND SAID FREE ENDS BEING WHEN SAID APPARATUS IS HELD IN A SUBSTANTIALLY VERTICAL POSITION LOCATED AT A HIGHER ELEVATION THAN THE LEVEL OF LIQUID IN SAID FIRST CHAMBER MEANS.