in ELECTRICAL EXCITATION OF MUSCLE 263 



other, there is injury to the muscle-substance, caused by mechani- 

 cal impact. 



Especially remarkable in this method of experiment is the 

 relaxation immediately consequent on break of current at the 

 effective kathode ; it can in no respect be distinguished from 

 the anodic closure relaxation, and, as we shall see, must in all 

 probability be regarded as an equivalent process. 



With regard to time, the order of succession of these pheno- 

 mena is that the kathodic half contracts immediately upon 

 closure, after which the anode begins to relax. Similarly, on 

 opening the anodic break excitation, characterised by a strong 

 rapid contraction of the section of ventricle affected, the 

 kathodic opening effect follows, and like the anodic make 

 produces relaxation of the previously contracted parts. There 

 is thus a coincidence between the effects of the kathodic 

 make and anodic break excitation on the one hand, and the 

 anodic make and kathodic break on the other. 



It is important to the significance of the kathodic opening 

 relaxation to observe it at its best upon fresh, excitable prepara- 

 tions, and in a few successive makes or breaks only. The effect 

 grows weaker and more obscure in proportion with the length of 

 closure, or frequency of stimulation, with uniform direction and 

 strength of current, and finally it fails altogether. Whatever 

 means of excitation may be employed, we have observed 

 this to be especially conspicuous in certain cases where, 

 after double ligaturing of the apex of the heart, resulting in 

 pronounced contraction, the effect occurred on one side only 

 with subsequent passage of current. The entire descending 

 current of a Daniell cell produced in this case a marked (anodic) 

 relaxation at the base of the otherwise uninjured ventricle, 

 extending only over a very small portion of it. Closure of 

 the ascending current produced no effect, or at most resulted in 

 a weak contraction of the previously relaxed upper section, while, 

 on the other hand, after a prolonged closure of about 4 sees., the 

 kathodic opening relaxation appeared at the base with great dis- 

 tinctness, though only in a few consecutive excitations. Having 

 once become aware of this effect, we repeatedly obtained the 

 same result on the normal heart immediately after attach- 

 ing the canula, when the tonic contraction had developed 

 itself. Two conditions are here essential : first, the preparation 



