iv ELECTROMOTIVE ACTION IN MUSCLE 443 



It was soon observed that living muscle, traversed by current, 

 behaves in this respect very differently from dead organic, or 

 inorganic, bodies, more especially in that positive, as well as 

 negative, after-currents appear under some conditions. For the 

 investigation of polarisation effects in muscle, du Bois-Eeymond 

 generally used the gracilis and semimembranosus muscles, 

 stretched conveniently. A pair of nori-polarisable electrodes 

 on each side served to lead in the polarising current, and to lead 

 off the polarisation current. The second pair were usually placed 

 between the others, within the intrapolar area. A special con- 

 trivance made it possible to alter the "period of closure "- i.e. 

 the time during which the polarising current was sent through 

 the object to be polarised from O'OOl to 20 sees. The same 

 contrivance effected closure of the galvanometer circuit after 

 breaking the battery circuit at a minimal and constant 

 interval. 



The secondary electromotive effects observed under these 

 conditions of experiment in the muscle are essentially dependent 

 on the density and duration of the primary current, while they 

 are much confused from the persistent interference of negative 

 and positive action. " With a current density lower than that 

 of two Groves, and with quite a short closure, no polarisation is, as 

 a rule, perceptible in the galvanometer. The first traces found 

 with one Daniell and 1 sec. closure are negative. The first 

 positive traces, on the other hand, first appear with two Groves, 

 and about 0'3 sec. closure." 



With an increasing period of closure, du Bois-Eeymond found 

 that the positive polarisation quickly reached its maximum, to 

 decrease more slowly, and pass over into negative polarisation, which 

 on its side again rises to a maximum. He fixes the " critical 

 point " of closure as that at which positive passes into negative 

 polarisation. The strongest positive polarisation in these experi- 

 ments was at a closure of 0*0075 sees, with 20 Groves (!), the 

 strongest negative polarisation at 10 minutes' closure of 1 Grove. 

 Short impacts of current (induction shocks) produce only positive 

 polarisation. 



Both positive and negative polarisation are very .persistent, 

 and sometimes outlast the opening of the polarising current for 

 20 minutes or more. If they are initiated at the critical point, 

 du Bois-Eeymond not infrequently observed a diphasic variation, 



