188 



ELECTRO-PHYSIOLOGY 



CHAP. 



current is considerably increased in the sequel, no essential 

 change can be observed in the response of the muscle, unless it 

 be that the opening contraction then appears vigorously after only 

 a short duration of closure. With any effective intensity of 

 current a period of 1-2 sees, is usually sufficient to cause 

 perceptible shortening of the muscle ; but the effect increases 

 within certain limits, if the closure is lengthened with un- 

 altered direction and intensity of current. It is to be noticed 

 that the magnitude of the break contraction diminishes very 

 rapidly with repeated excitation of the same preparation ; this 

 seems to coincide with the extremely slow subsidence of all 

 excitation phenomena, and thus of the persistent opening con- 



Fio. 79. Contraction curve of adductor muscle of Anodonta on excitation with the constant cur- 

 rent, a, Immediately after preparation (pronounced tonus) ; b, 4 hours later, after relaxa- 

 tion of the muscle ; (s), closure ; (o), opening of current. 



traction also, since it is minutes before, at uniform loading, 

 the shortened muscle resumes its original proportions. Under 

 these conditions it is obvious that only in a very limited sense 

 can there be any comparison of the results of repeated excitation 

 of one and the same muscle under rapidly alternating experi- 

 mental conditions (e.g. differences of closure and current inten- 

 sity), since from the extreme slowness of relaxation the first 

 experiment alone can, as a rule, be taken into consideration. 

 We may assume that other smooth muscles with a developed 

 " tonus " will react in the same way towards galvanic currents as 

 the preparation in question. Morgen (9) experimented with a 

 circular piece of frog's stomach, which was suspended between 

 two metal hooks in a moist chamber while still connected with 

 the mucosa or after freeing it of the latter, so that the changes 



