A tissue processing apparatus configured to process biological tissue by treating the biological tissue with a plurality of reagents and then with an embedding medium, the tissue processing apparatus comprising: an extraction device, wherein the extraction device is an inlet tube configured to take reagent out of a reagent receptacle via a reagent opening , when inserted into the reagent receptacle; a measurement probe , mounted to the inlet tube , that includes two measurement surfaces spaced apart from each other, wherein the measurement probe is configured to be inserted into the reagent receptacle so that the two measurement surfaces are at least partially immersed in reagent contained in the reagent receptacle; wherein the tissue processing apparatus is configured to provide an indication to a user to connect the extraction device of the tissue processing apparatus to the reagent receptacle containing reagent of a specified type and concentration; after the user has connected the extraction device to the reagent receptacle: using the two measurement surfaces of the measurement probe to obtain at least one electrical measurement of reagent contained in the reagent receptacle before reagent is taken out from the reagent receptacle by the extraction device; determining, based on the at least one electrical measurement, a concentration and/or a type of reagent contained in the reagent receptacle; and if the determined concentration and/or type of reagent contained in the reagent receptacle does not match the specified concentration and/or type, provide an indication to the user that the reagent contained in the reagent receptacle connected to the extraction device does not match the specified concentration and/or type. an extraction device, wherein the extraction device is an inlet tube configured to take reagent out of a reagent receptacle via a reagent opening , when inserted into the reagent receptacle; a measurement probe , mounted to the inlet tube , that includes two measurement surfaces spaced apart from each other, wherein the measurement probe is configured to be inserted into the reagent receptacle so that the two measurement surfaces are at least partially immersed in reagent contained in the reagent receptacle; wherein the tissue processing apparatus is configured to provide an indication to a user to connect the extraction device of the tissue processing apparatus to the reagent receptacle containing reagent of a specified type and concentration; after the user has connected the extraction device to the reagent receptacle: using the two measurement surfaces of the measurement probe to obtain at least one electrical measurement of reagent contained in the reagent receptacle before reagent is taken out from the reagent receptacle by the extraction device; determining, based on the at least one electrical measurement, a concentration and/or a type of reagent contained in the reagent receptacle; and if the determined concentration and/or type of reagent contained in the reagent receptacle does not match the specified concentration and/or type, provide an indication to the user that the reagent contained in the reagent receptacle connected to the extraction device does not match the specified concentration and/or type. using the two measurement surfaces of the measurement probe to obtain at least one electrical measurement of reagent contained in the reagent receptacle before reagent is taken out from the reagent receptacle by the extraction device; determining, based on the at least one electrical measurement, a concentration and/or a type of reagent contained in the reagent receptacle; and if the determined concentration and/or type of reagent contained in the reagent receptacle does not match the specified concentration and/or type, provide an indication to the user that the reagent contained in the reagent receptacle connected to the extraction device does not match the specified concentration and/or type. <EOS>