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In the skeletal muscle of cats, semispherical stimulating electrodes having a radius of 1.2 mm deliver a mean threshold current of 0.15 mA, corresponding to 1.7 mA/cm2. These values are doubled within a period of four weeks after chronic implantation. In the case of non-polarizable electrodes the mean threshold voltage increases from 108 mV to 171 mV. The lowest individual values range between 50 mV and 60 mV at the time of implantation. The highest value is around 500 mV after four weeks. The high values have been observed with strongly polarizing ELGILOY electrodes. The chronic threshold energies vary between 3 x 10(-8) Ws for activated vitreous carbon electrodes and 17.5 x 10(-8) Ws for ELGILOY electrodes. There are two reasons for the low threshold energy of activated vitreous carbon electrodes. One reason is their low polarization, and the other is their better compatibility. Connective tissue layers with a thickness between 25 micron and 50 micron are found around well healed carbon electrodes.

Electrodes made of vitreous carbon are inert, corrosion-resistant, inactive to electrocatalytic reactions and are especially biocompatible. Upon activation, they attain a capacitance of 20 to 40 mF and become "non-polarizable". Therefore, they should be particularly suitable as stimulating and sensing electrodes for cardiac pacemakers. The connective tissue layer that develops around the electrode because of the foreign-body reaction is less than 100 micron thick. The threshold rise, through lower than that of conventional Pt-Ir or ELGILOY electrodes, cannot be attributed exclusively to the connective tissue layer that is formed. Under favourable conditions, the threshold in animal experiments remains below 525 mV. Blood-spaces adjoining the electrodes are found at higher chronic threshold values.

For the determination of glucose in body fluids, the electrocatalytic sensor, besides the enzyme sensor, is quite suitable, particularly for long-term intracorporeal operation. The measuring response is disturbed by the fluctuating concentrations of the interfering substances that are simultaneously present in body fluids. However, the disturbance can essentially be controlled, as is shown in the case of amino acids. Their marked influence on glucose oxidation is suppressed at a membrane-covered sensor electrode by the use of a potential step method.