CH. XII.] 



THE DIPHASIC VARIATION. 



149 



of a second, and is over long before the other changes in form, etc., are 

 completed. Sir .1. Bunion Sanderson gives the following numbers from 

 experiments with the frog's gastrocnemius. When the muscle is excited 

 through its nerve the electrical response begins ^ fl and the change of form 

 j^ second after the stimulation ; the second phase, that is, the return to 

 the previous condition, begins 1( y^ second after excitation. When the muscle 

 is directly excited, the latent period is much shorter, the change in form 

 beginning ^ and the electrical change in less than ^^ second after 

 excitation. 



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 photographic curves are placed one over the other so that the beginnings 

 coincide. (liunliin Sanderson.) 



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

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

 on the uninjured 

 surface and the 

 other on the cut 

 end (see fig. 173), 

 the electrical re- 

 sponse is a dif- 

 ferent one. 



Under these 

 circumstances, 

 the electrical 

 changeisamono- 

 phasic variation, 

 for when the 



muscle wave reaches ((/), this part of the muscle, owing to its 

 injured state, does not respond to the excitatory condition, and 

 the electrical response is also extinguished. 



The grey curve in fig. 1 7 2 is the graphic record of the change 

 as revealed by the capillary electrometer. It will be seen that the 

 ascending limb of the curve is identical in the two cases, but that 

 the second phase is absent. From the point at which the diphasic 

 curve approaches its culmination the injury curve diverges from 

 it, continuing to ascend ; the line soon after becomes horizontal. 



