Measuring system consisting of a measuring device for measuring the flue gas components of a gas sample with a control unit and a measuring gas probe for taking the gas sample in a hot, dust-containing gas atmosphere, wherein the measuring gas probe comprises - a flange for placing the measuring gas probe on a furnace inlet chamber containing the gas to be measured, - a tubular, coolant-cooled probe body having a tubular outer wall, a bottom closing one end face and a cover closing the other end face, - with coolant supply and coolant return so that coolant can flow in the interior of the probe body, - a first sampling tube which extends in the interior of the probe body parallel to the longitudinal axis of the probe body and passes through the cover, wherein an end of the sampling tube remote from the cover is bent laterally so that the end is formed as a first sampling opening for gas extraction laterally from the tube outer wall, - a second sampling tube extending substantially parallel to the first sampling tube and of identical construction to the first sampling tube and having a second sampling opening, - whereby the two sampling tubes (30, 40) are cooled by the coolant, - and the sampling tubes (30, 40) pass through the cover for connection to the measuring device, wherein the two sampling tubes of the measuring gas probe are connected to the measuring device via gas lines, characterised in that - that gas shut-off valves are provided for the selective connection of one of the sampling tubes to the measuring device and tube back-flushing devices are provided for flushing the sampling tubes, - and in that the control unit is arranged to control the measuring gas probe in such a way that the gas sample is taken through one of the two sampling tubes and during sampling, the other sampling tube is cleaned by the tube back-flushing device. - a flange for placing the measuring gas probe on a furnace inlet chamber containing the gas to be measured, - a tubular, coolant-cooled probe body having a tubular outer wall, a bottom closing one end face and a cover closing the other end face, - with coolant supply and coolant return so that coolant can flow in the interior of the probe body, - a first sampling tube which extends in the interior of the probe body parallel to the longitudinal axis of the probe body and passes through the cover, wherein an end of the sampling tube remote from the cover is bent laterally so that the end is formed as a first sampling opening for gas extraction laterally from the tube outer wall, - a second sampling tube extending substantially parallel to the first sampling tube and of identical construction to the first sampling tube and having a second sampling opening, - whereby the two sampling tubes (30, 40) are cooled by the coolant, - and the sampling tubes (30, 40) pass through the cover for connection to the measuring device, wherein the two sampling tubes of the measuring gas probe are connected to the measuring device via gas lines, characterised in that - that gas shut-off valves are provided for the selective connection of one of the sampling tubes to the measuring device and tube back-flushing devices are provided for flushing the sampling tubes, - and in that the control unit is arranged to control the measuring gas probe in such a way that the gas sample is taken through one of the two sampling tubes and during sampling, the other sampling tube is cleaned by the tube back-flushing device.