can be seen the sterilization chamber 2 is of the horizontal axis type and is passed through vertically by a duct 5 consisting of a tube screwed at the bottom onto a threaded union 6 on the bottom of the chamber at the top the duct 5 passes through the wall of the sterilizer and at its end sealingly engages in a manner known per se not shown in the drawings with two ball valves 8 and 9 arranged in series and separated by a prechamber 7 the latter has been designed so as to allow the introduction of bioindicator samples into the sterilization chamber 2 which contains the sterilizing agent and therefore cannot be placed into direct communication with the exterior in a manner which is safe for the operator and the process the opening and consequent closing of the valve 9 allows the introduction of the bioindicator sample into the upper prechamber 7 while the opening and consequent closing of the valve 8 causes the sample to fall by means of gravity into the sterilization chamber 2 inside the duct 5 at the bottom also the duct 5 passes through the wall of the sterilizer and its bottom end is connected to two ball valves 10 and 11 arranged in series and also separated by a prechamber 7 a.