in ELECTRICAL EXCITATION OF MUSCLE 261 



wave of relaxation is so slow that its progress may conveniently 

 be followed with the eye. For the rest it varies considerably. 

 While in one case the wave requires several seconds to spread 

 over the small tract implicated, averaging 5 to 7 mm., in other 

 cases a fraction of a second will be sufficient. This, again, depends 

 essentially upon the degree of tonus present, and one might say~ 

 that the more pronounced this is, the slower will be the diffusion 

 of relaxation from its starting-point. If the excitation is repeated 

 with unchanged direction of current, or if the current is left 

 closed, it is easy to see that the rate of propagation of the anodic 

 wave increases in time up to a certain value which it soon 

 reaches ; if the current is reversed it diminishes again quickly. 



The period of latent excitation, generally speaking, varies in 

 the same sense. The relaxation at the anode, as is immediately 

 evident, never begins precisely at the moment of closure of the 

 current, but is always preceptibly, often considerably, later, so 

 that a latent period of one or more seconds is by no means rare. 

 In many cases it may be shorter, but is never so brief that it 

 cannot be detected directly by the eye. 



If the experiment is made with preparations, which db 

 initio exhibit a marked degree of tonic contraction, the relaxa- 

 tion starting from the anode appears to be the sole visible effect of 

 the current, a previous increase of contraction under such circum- 

 stances being at all events imperceptible. That such increase 

 is, however, present under certain conditions of relaxation, 

 may be ascertained in all cases in which there is primarily 

 only a medium degree of tonic contraction. For then, with 

 closure of an adequate current, the ventricle may be seen to con- 

 tract in the first place simultaneously, in all its parts, after which 

 only the peristaltic relaxation from the anode commences. 



If the contraction in this case proceeds from the kathode, as 

 may be affirmed on the strength of experiments to be described 

 later, the conclusion which appears from the reaction is that 

 the latent period of the kathodic closure excitation is smaller, 

 while the rapidity of transmission is more rapid, than in anodic 

 closure. On the other hand, the latter seems to take effect at 

 a lower intensity of current, e.g. we have repeatedly found, 

 with a weak tonus, that a (local) relaxation began earlier, 

 i.e. with less rheochord resistance, than in the closure contraction 

 in question. 



