80 CONTRACTILE ELEMENTS. 



muscle in which contraction occurs passes perfectly into the 

 second form without meeting with any obstacle, it gives rise 

 to heat only ; but if, as in the normal condition, it cannot 

 perfectly attain this form, on account of the resistance which 

 it has to overcome, we find that, on hardening, it evolves 

 only a part of the heat produced by the combustion of which 

 it is the seat, the rest being transformed into mechanical 

 labor (Beclard). 



Electro-motor Power. We have seen that under the 

 first form the muscle possesses an electro-motor power, by 

 means of which its surface is positive, in relation to its in- 

 terior. 



If the wires of a galvanometer are placed in contact w r ith 

 a muscle under the first form, one with its surface or longi- 

 tudinal section, the other with its transverse section ; so as to 

 ascertain the current, which in this case is directed from the 

 former surface to the latter in the galvanometrical circuit, 

 and the muscle is then made to pass into the second form ; we 

 find that the needle, which the current at first caused to 

 swerve, returns to zero, and oscillates on this side and above 

 it (Du Bois-Reymond). Thus the electro-motor condition 

 of the muscle is changed : this is what is called negative 

 variation of the current of a contracted muscle. But, as 

 we have seen that no conclusion can be drawn from the 

 electro-motor power of the muscle under its first form, so 

 nothing positive can be affirmed as to its negative variation 

 in the second form, for it is still impossible to say whether 

 the latter is due to the suppression of the primitive current, 

 to its simple diminution, or even to its being replaced by a 

 contrary current. 



Du Bois-Reymond, who discovered negative variation, 

 considered this phenomenon as the result of the weakening 

 of the normal current (electro-motor) of the muscle when in 

 the state of repose, which weakening would allow of the 

 manifestation of a contrary current, due only to the second- 

 ary polarities of the wire of the galvanometres (polarization 

 of the electrodes. See Wundt's "Physique"). Matteucci 

 believed, on the contrary, in a complete inversion of the nor- 

 mal current of repose. Experience has shown that Du Bois- 

 Reymond was right, for, by constructing electrodes which 

 undergo no polarization (amalgamated zinc, dipped in a 

 solution of sulphate of zinc, Regnault), it has been proved 

 that, when the muscle passes into the second form, there 

 results only suppression, or even only diminution, but never 



