THE ELECTRICAL RESPONSE. 423 



tetanic excitation. The change, however, was less in amount than in 

 injured muscle, and irregular in development, and moreover lasted longer 

 after the excitation ceased than when the distal electrode was on an 

 injured surface. As has already been pointed out, du Bois-Reymond 

 regarded the " negative variation " as a diminutional effect, using the 

 word negative in its algebraic sense. In order to explain its presence 

 when there was no muscle current, he had recourse to the auxiliary 

 theory, that the " natural cross-section," i.e. the end surface of every 

 muscle, presents peculiarities of molecular structure, which he desig- 

 nated by the term " parelectronomy." He was thus able to account in 

 the most ingenious way for the irregularities he observed, as resulting 

 from the interference of parelectronomic effects having their seat in the 

 ends of the fibres, with the normal ones. 



As has been already stated, the molecular theory of du Bois-Eey- 

 mond is not now accepted by physiologists. The other theory, however, 

 with which it is associated, namely, that which attributes the negative 

 variation, no less of injured than of uninjured muscle, to the summation 

 of individual electrical responses evoked by instantaneous stimuli, has 

 not as yet, so far as I know, been questioned. 



In the case of injured muscles with the leading-off contacts, as 

 in Fig. 236, A, the monophasic character of the single response appears 

 to be adequate to explain the course of , , 



the tetanic variation ; but as regards un- A 



injured muscles it is at first sight difficult 



to see why the summed effect of a series ' 1 -B 



of diphasic variations should take the direc- FIG. 236. X denotes the seat of 

 tion of the first phase, as was found to be excitation ; the upright lines 

 the case in the gastrocnemius by du Bois- $$&S^ f the M '. 

 Reymond. Many years ago (1868), Her- 

 mann suggested that when it occurs, it is due to the fact that 

 every excitatory wave becomes weaker as it progresses. Soon after- 

 wards, Bernstein, as the result of his rheotome experiments, was led 

 to believe this surmise to be correct, and Hermann, later, in repeating 

 an old experiment, showed that in a sartorius with the electrodes 

 arranged as in Fig. 236, B, there is usually a " decremental " tetanic 

 effect the proximal contact becoming negative to the distal. 1 The 

 total difference of potential in the tetanic response of an uninjured 

 muscle was explained by him, on the supposition that each excitatory 

 wave becomes weaker as it progresses, the second phase of each 

 diphasic effect being weaker than the first. The complete absence of 

 negative variation in tetanus of the human forearm indicates that in 

 perfectly normal muscles there is, as Hermann says, no decrement. 2 



The tetanic variation, or, as Hermann calls it, the " tetanic action- 

 current," can be observed in different ways. When a galvanometer of 

 high resistance is used, the needle being so damped as to be nearly 

 aperiodic, only T ^ part of the current passing through the bobbins, 

 the spot assumes a position which corresponds to the integral difference 

 of potential, the value of which can be easily determined from the 

 deflection with the aid of a compensator. As the time required for the 



1 Hermann's "Handbuch," Bd. i. S. 214; du Bois-Reymond, "Gesamuielte Abhand- 

 lungen," Bd. ii. S. 560. 



2 "Im ganz normalen Muskel ist kein Decrement der Erregungswelle vorhanden," 

 loc. Git.. S. 224. 



