A tool for applying ink to, and for drying and marking, biological tissue, the tool comprising: a cylindrical body comprising a distal opening , a marker shaft comprising a marker felt tip disposed at a distal end of the marker shaft , the marker shaft comprising the marker tip being movable between a retracted position wherein the marker tip is within the body and an extended position wherein the marker tip is outside the body for marking the tissue; a manual valve to selectably dispense a drying gas from a gas source through the distal opening of the cylindrical body onto the tissue, and a lever configured to open and close the manual valve , and characterized in that the tool further comprises a stop block carried by the marker shaft , a first plunger arm extending into the cylindrical body from the lever , a second plunger arm disposed at a distal end of the lever , and a spring configured to urge the lever away from the cylindrical body , and wherein the manual valve is configured to be open and closed via the first plunger arm, and wherein the second plunger arm is configured to interfere with the stop block such that, when the marker tip is in the extended position, the lever is deflected radially outward and, when the marker tip is in the retracted position, the second plunger arm is not deflected by the stop block so that, in order to move the lever toward the cylindrical body , the marker tip must be retracted such that the stop block does not prevent incursion of the second plunger arm , the first and second plunger arms thereby forming an interlock configured to prevent the marker shaft comprising the marker tip moving to the extended position when the manual valve is dispensing the drying gas and to prevent dispensing of drying gas when the marker shaft comprising the marker tip is in the extended position. a cylindrical body comprising a distal opening , a marker shaft comprising a marker felt tip disposed at a distal end of the marker shaft , the marker shaft comprising the marker tip being movable between a retracted position wherein the marker tip is within the body and an extended position wherein the marker tip is outside the body for marking the tissue; a manual valve to selectably dispense a drying gas from a gas source through the distal opening of the cylindrical body onto the tissue, and a lever configured to open and close the manual valve , and characterized in that the tool further comprises a stop block carried by the marker shaft , a first plunger arm extending into the cylindrical body from the lever , a second plunger arm disposed at a distal end of the lever , and a spring configured to urge the lever away from the cylindrical body , and wherein the manual valve is configured to be open and closed via the first plunger arm, and wherein the second plunger arm is configured to interfere with the stop block such that, when the marker tip is in the extended position, the lever is deflected radially outward and, when the marker tip is in the retracted position, the second plunger arm is not deflected by the stop block so that, in order to move the lever toward the cylindrical body , the marker tip must be retracted such that the stop block does not prevent incursion of the second plunger arm , <EOS>