142 



THE ELECTRICAL PHENOMENA OF MUSCLE 



[CII. XII. 



a minute fraction of a second* later this balance is upset, and now 

 when the wave reaches the point (d), that point is positive to (p), 

 and the galvanometer needle moves in the opposite direction. 



The electrical variations may also be investigated by the capillary 

 electrometer; the mercury moves first in one direction, and then 



the other. The deep black curve in the next figure (fig. 172) 



in 



FIG. 172. Diphasic curve (black) of the normal sartorius. The grey curve is the monophasic curve of 

 the same muscle when one electrometer contact was placed on the injured end. The two photo- 

 graphic curves are placed one over the other so that the beginnings coincide. (Burdon Sanderson.) 



shows the record obtaining by photographing the movement of the 

 column of mercury on a rapidly travelling photographic plate. 



The capillary electrometer has the advantage of giving us the means of measur- 

 ing the time of onset and duration of the electrical disturbance, and experiments 

 made with this instrument confirm the earlier experiments made with the rheotome. 

 They show that the change only lasts a few thousandths of a second, and is over 

 long before the other changes in form, etc., are completed. Sir J. Burdon Sander- 

 son gives the following numbers from experiments with the frog's gastrocnemius. 

 When the muscle was excited through its nerve the electrical response began y-j^ny and 

 the change of form T ^ second after the stimulation ; the second phase of the 

 electrical response began j--^^ second after excitation. When the muscle was 

 directly excited, the latent period was much shorter, the change in form beginning 

 and the electrical change in less than y^ second after excitation. 



G 



FIG. 173. 



If, however, instead of examining the electrical change in the 

 muscle in the manner depicted in fig. 171, one electrode is placed on 



* The time will vary with the distance between (/>) and (d}. 



