Surgical device comprising: an instrument for cutting of biological tissue, an apparatus for supply of the instrument with electrical HF power having a frequency between 100 kHz and 5 MHz, wherein the instrument comprises at least one HF electrode, which is connected to the apparatus via a line in order to be supplied with HF power and to produce an HF spark for cutting the biological tissue under creation of a light phenomenon, characterized in that at least one light receiving device aiming at an area comprising the light phenomenon is assigned to the instrument and in that the device comprises the following elements: an analysis device for determination of light features of the light created by the influence on the biological tissue by means of analysis of the light created at the electrode during occurrence of an HF spark and a discriminator device for assignment of light features of the light, which is created during the influence, to tissue features of the biological tissue subject to the influence and thereby for differentiation between healthy tissue and pathologic tissue, wherein the light features are signatures gained from: - the spectrum of the light of the plasma, - portions of the spectrum and/or - spectral lines, wherein the signatures are: - intensity ratios of selected spectral lines or - ratios between different terms, wherein the terms are in turn: - sums, - differences, - products, - integrals over sub-spectra and/or - other terms of intensities of different spectral lines or sub-spectra. an instrument for cutting of biological tissue, an apparatus for supply of the instrument with electrical HF power having a frequency between 100 kHz and 5 MHz, wherein the instrument comprises at least one HF electrode, which is connected to the apparatus via a line in order to be supplied with HF power and to produce an HF spark for cutting the biological tissue under creation of a light phenomenon, characterized in that at least one light receiving device aiming at an area comprising the light phenomenon is assigned to the instrument and in that the device comprises the following elements: an analysis device for determination of light features of the light created by the influence on the biological tissue by means of analysis of the light created at the electrode during occurrence of an HF spark and a discriminator device for assignment of light features of the light, which is created during the influence, to tissue features of the biological tissue subject to the influence and thereby for differentiation between healthy tissue and pathologic tissue, wherein the light features are signatures gained from: - the spectrum of the light of the plasma, - portions of the spectrum and/or - spectral lines, wherein the signatures are: - intensity ratios of selected spectral lines or - ratios between different terms, wherein the terms are in turn: - sums, - differences, - products, - integrals over sub-spectra and/or - other terms of intensities of different spectral lines or sub-spectra. an analysis device for determination of light features of the light created by the influence on the biological tissue by means of analysis of the light created at the electrode during occurrence of an HF spark and a discriminator device for assignment of light features of the light, which is created during the influence, to tissue features of the biological tissue subject to the influence and thereby for differentiation between healthy tissue and pathologic tissue, wherein the light features are signatures gained from: - the spectrum of the light of the plasma, - portions of the spectrum and/or - spectral lines, - the spectrum of the light of the plasma, - portions of the spectrum and/or - spectral lines, wherein the signatures are: - intensity ratios of selected spectral lines or - ratios between different terms, - intensity ratios of selected spectral lines or - ratios between different terms, wherein the terms are in turn: - sums, - differences, - products, - integrals over sub-spectra and/or - other terms of intensities of different spectral lines or sub-spectra. - sums, - differences, - products, - integrals over sub-spectra and/or - other terms of intensities of different spectral lines or sub-spectra.