Pflüger's Laws

PFLÜGER'S LAWS (Pflüger), proposed by Pflüger in 1859, are laws establishing the dependence of functional changes in body tissues on the strength and direction of a direct electrical current acting upon them. These laws can be formulated as follows: 1) upon closing the circuit, a wave of excitation always arises only at the cathode; 2) during the passage of current through the tissue, excitability is increased at the cathode and decreased at the anode; 3) upon opening the circuit, the decrease in excitability at the anode is replaced by a wave of excitation originating there; 4) upon opening the circuit, the excitability at the cathode turns out to be decreased; and 5) the intensity of the polar influences of the current depends on its strength. Catelectrotonus refers to the changes occurring beneath the cathode in the direction of increased excitability, while anelectrotonus refers to changes beneath the anode in the direction of decreased excitability. Pflüger also gave the following formulation for his 1st and 3rd laws: tissue is excited either by the onset of catelectrotonus or by the disappearance of anelectrotonus. If direct current electrodes are applied to the motor nerve of a muscle, then depending on whether there is a region of decreased excitability in the path of the excitation wave, we will observe a muscle contraction (+) or the latter will not take place (-) (see table). Current Strength | Descending Current * | Ascending Current ** | Make | Break | Make | Break | + | + | + | + | + | + | + | - * Cathode closer to the muscle. ** Anode closer to the muscle. After Pflüger, additions were made to his laws; thus, Verigo proved that with prolonged action of the current, the increase in excitability at the cathode is replaced by a drop in excitability, which can cause non-conductivity and death of the nerve. Pernau showed that the secondary decrease in excitability at the cathode can be considered as parabiosis (see). Vведенский found that at a considerable distance from the primary poles, secondary ones with reversed signs are established (perielectrotonic phenomena). The existing theories of cat- and anelectrotonus, explaining the observed phenomena from the standpoint of current transfer (Loeb, Lazarev) or changes in the concentration of hypothetical fibrillar acid (Bete), do not yet provide an opportunity to correctly interpret the phenomena of the action of an electrical current on tissues and thereby approach the most cardinal question of modern physiology—the essence of excitation and inhibition phenomena.