An apparatus (14) for supplying a medical instrument (15) for the treatment of biological tissue (11) due to the action of a plasma (28) is disposed, in accordance with the invention, in a special manner for the ignition and the stable development of a plasma (28) on the electrode (27) of the instrument (15). To accomplish this, the apparatus (14) comprises a control device (23) that, during an ignition test, limits—；preferably in an instrument-specific manner—；the current deliverable to the instrument (15) and/or limits the electrical power to be output to the instrument (15), and/or, in doing so, works with a reduced operating voltage. With this measure, a rapid, stable plasma development with minimal spark play is achieved with a large variety of connectable instruments (15a-15e).
