Studies on the electric threshold in human nerve and muscle.

The electric threshold is widely used as a criterion indicating the intensity factor of excitability of nerve and muscle. For consideration of the electric excitation of these tissues, factors other than the above, such as the time factor and the slope factor, appear to be important (Suzuki (16)). These factors have been studied thoroughly in the first half of this century. Observations have also been made on human body, being used as criterions the threshold of Cathode closure contraction (CaCC), Cathodal opening contraction (Ca0C), Anode closure contraction (AnCC), and Anodal opening contraction (AnOC), the rheobase, the chronaxie and the A constant. They are now in use for clinical diagnosis. Since, however, the threshold must represent quantitatively the current which stimulates the nerve or muscle, its exact value cannot be determined in the human body by the same procedures as are used in its measurement in excised preparations. The most notable difference is the fact that, in human body, the stimulating current is delivered through the skin. In measuring the chronaxie in human body, Lapicque (1) and others (2, 3) used arrangements which cancelled the electric resistance of the skin against the stimulating current. The arrangement, however, fell short of perfection at the degree of its achievements, since the skin had other electric component not negligible in determining the accurate threshold. Fortunately, however, the study of electrical characters in human skin has recently been developed to such an extent that the cause of the defects in the measurement of threshold as described above has been clarified (4, 5, 6, 7, 8, 9). On the basis of this knowledge the author has studied to eliminate the obstructions inherently existing in the skin, and derised a method determing accurately the threshold of nerve or muscle in human body (10, 11, 12). This method is called the "Balancing Network Method."