The invention relates to an instrument head, comprising: an exit opening (23); a first feed line (11) for the feed of a first fluid; a second feed line (12) for the feed of a second fluid; a reservoir (24) for storing the fluid fed via the second feed line (12); wherein the reservoir (24) is in fluid communication with the first feed line (11) and/or is adapted to be brought in fluid communication with the first feed line (11) via at least a valve (25) arranged in the instrument head, to deliver fluid stored in the reservoir (24) via the exit opening (23).