ELECTRICAL CHANGES IN MUSCLE 



231 



can be no difference of potential between them. The excitatory condition 

 then passes off, first at the base and then at the apex. There is thus a small 

 period of time in which the apex is still contracted or excited while the base 

 is relaxed, and the apex is therefore negative to the base. This terminal 

 negativity of the apex is shown on the photograph by the excursion of the 

 column of mercury away from the point of the capillary. If one terminal, 

 e.g. the apex, be injured, we obtain quite a different variation, which is shown 

 in Fig. 87, B. It is evident from this figure that the electrical sign lasts practi- 



Fia. 87. Electrometer records of the electrical variations in a tortoise ventricle, 



excited to beat rhythmically by single shocks. 

 A, Ventricle uninjured. B, One leading off spot injured. (B. SANDERSON.) 



cally as long as the mechanical sign of the excited state, and that we are not 

 justified in regarding the first spike of the diphasic variation as indicative 

 of an excitatory wave attended by an electrical change which is independent 

 of the succeeding mechanical change. 



The only difference between the electrical changes in this case and in that 

 of voluntary muscle is that in the latter all processes are very much quicker, 

 so that as a rule the point a (Fig. 84) has ceased to be negative before the 

 negativity of b has attained its full height, and there is thus no prolonged 



fquipotential stage. 

 Although in the case of the slowly contracting ventricle of the tortoise, the record 

 obtained of the electrical changes accompanying its contraction by means of the capillary 

 electrometer shows with great clearness the diphasic nature of the variation, and there- 

 fore the wave character of the electrical change, considerable difficulty is experienced 

 sometimes in recognising that the ' spike ' record of the electrical change in voluntary 



