316 ELECTRO-PHYSIOLOGY CHAP. 



is required before, when one wave of contraction has expired, those 

 conditions are restored which are essential for bringing about a 

 new wave of excitation (Engelmann). 



The facts submitted above re discharge of a rhythmical 

 succession of contraction waves during protracted closure of a 

 battery current, do not contradict this conclusion. Expressed in 

 general terms, the recovery of an original state of the excitable, 

 conducting substance takes place only when a new wave of 

 contraction passes during the continuance of an uninterrupted 

 stimulus. 



Yet, in so far as the ratio and time-relations of the assimilatory 

 and dissimilatory processes in living matter are correlative, this 

 would apply to intermittent, as well as to uninterrupted, causes of 

 excitation. As regards the latter we need only refer to the wide 

 distribution of rhythmical processes of movement, depending, as 

 may be shown, in many cases upon the capacity of certain kinds of 

 protoplasm to convert a constant stimulus into rhythmical excita- 

 tion. This capacity is more or less developed from the relatively 

 undifferentiated protoplasm of protozoa (contractile vacuoles) up 

 to striated muscles, but with striking differences of degree. Thus 

 the non-ganglionated, cardiac muscle pulsates rhythmically not 

 merely with uniform mechanical or chemical stimuli, but also 

 under the action of the constant current, and the same applies, 

 though in a much lesser degree, to striated skeletal muscle. 

 Without entering on the question of the specific cause of the 

 rhythm in these and similar cases, we may point out that the 

 occurrence of a rhythmical succession of contractions during 

 sustained closure of the current is a very convincing proof that 

 the excitation process is persistently maintained during electrical 

 stimulation. The electromotive effects of sending . current into 

 the muscle, known, after du Bois, as secondary electromotive 

 manifestations (which will be discussed below), are also of great 

 importance in this connection. 



The second fundamental proposition is the law of the exclus- 

 ively polar action of every ordinary electrical current, to the effect that 

 the excitatory process is primarily discharged at the physiological 

 kathode only (in the majority of cases) at and during closure of the 

 exciting current, at the physiological anode only, at and subsequently 

 to break of the current. A remarkable exception in localisation of 

 electrical excitation is however shown to exist in many, perhaps 



