MUSCLES, NERVES, AND ELECTRICAL ORGANS. 173 



galvanometer, it being 1 required to compare in experiments which, 

 followed each other immediately, the perhaps permanent deflection 

 due to a current of thirty Groves, with the ten thousand times feebler 

 movement produced by a current of a single Daniell lasting a few 

 thousandths of a second. I lost much time and trouble in the 

 attempt to read the two galvanometers, viz. the one for the 

 polarising current, and that for the secondary current, through the 

 same telescope. Besides the technical difficulties which this in- 

 volves, the observer is overburdened by having to do too many 

 things at the same time. I therefore recurred to the more simple 

 method of having the second galvanometer read by an assistant. 



7. Secondary Electromotive action of muscles in regard to its 

 dependence on the density and duration of the primary 

 current. 



Let us suppose the group of muscles, gracilis and semi-membra- 

 nosus, extended in the muscle -stretcher so firmly that they do not 

 perceptibly move in contraction, and the two pairs of electrodes 

 applied in the manner described, and the muscle-current compen- 

 sated. If the electrodes are applied symmetrically the muscle 

 current ascends; its electromotive force, although often insig- 

 nificant, frequently reaches 0-017 Raoult. 



If a current be now applied to the muscle for a longer or a shorter 

 time, the galvanometer circuit being 'doubly' open, and if the 

 galvanometer circuit be shut immediately after the battery circuit 

 has been doubly opened, any secondary electromotive action that 

 may have been excited in the muscle equalises J itself through the 

 galvanometer circuit, and is truly expressed by the deflection of the 

 galvanometer, provided the compensation remains undisturbed. If 

 the battery circuit is long closed, if the tension of the muscle is 

 diminished, or if strong contraction occurs, tl^is condition is not 

 always certainly fulfilled ; and besides, if a strong muscle-current is 

 to be compensated, the contraction leaves an after-effect. The 

 secondary electromotive actions are however generally too marked 

 to be mistaken for such disturbances. They are due to the internal 



1 [When any spot a on the surface of a moist conductor is negative to any other 

 spot 6, the current which exists from a to b is said sicJi abzugleichen by currents out- 

 side of it which are directed from 6 to a. The same expression is used of a current 

 which flows from 6 to a through a galvanometer of which the terminal electrodes are 

 applied to these spots. Whenever possible, the word ' dbgleichen ' is Englished by 

 the word ' equalise.' Ed.] 



