124 



THE ELECTRICAL PHENOMENA OF MUSCLE 



[CH. XI. 



The galvanometer is not the best instrument to employ to 

 demonstrate these facts ; the inertia of the needle may be so great 

 that it is impossible for it to catch and respond to the two phases. 

 Wedenski has made extensive use of the telephone instead, and the 



FIG. 142. 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.) 



sounds produced in it by the electrical changes in the muscle are 

 distinctly audible. An appeal to the eye, however, is generally 

 regarded as more satisfactory than one to the ear, and for this purpose 

 the capillary electrometer is the instrument most frequently em- 

 ployed, as its responses are immediate ; the mercury moves first in 

 one direction, and then in the other. The deep black curve in the 

 next figure (fig. 142) 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 

 show that the change only 

 lasts a few thousandths o*f 

 a second, and is over long 

 before the other changes 

 in form, etc., are com- 

 pleted. Sir J. Burdon 

 Sanderson gives the follow- 

 ing numbers from experi- 

 ments with the frog's 

 gastrocnemius. When the 

 muscle was excited through 

 its nerve the electrical 

 response began T7 % 7 and 

 the change of form T -$^ 



FIG. 143. second after the stimula- 



tion ; the second phase of 



the electrical response began r $fo second after excitation. When the muscle was 

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

 T / w and the electrical change in less than Ttnrsy second after excitation. 



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

 muscle in the manner depicted in fig. 141, one electrode is placed on 



