STIMULATION OF MUSCLE AND NERVE 157 



descending currents, the first contraction will 

 be on closure only. With ascending currents, 

 the first contraction will be on opening the 

 current. 



The explanation is that, with currents which 

 pass through the sartorius from end to end 

 the point of greatest density is the smaller, 

 lower end. This is cathodal in descending 

 currents, anodal in ascending currents. 



EFFECT OF THE ANGLE AT WHICH THE CURRENT 

 LINES CUT THE MUSCLE FIBRES 



Connect non-polarizable electrodes through 

 a key with a dry cell. Build on a glass plate 

 with normal saline clay two parallel walls a 

 little longer than the sartorius muscle and 

 one centimetre apart. Join the ends with 

 wax, to make a rectangular trough. Kemove 

 a sartorius muscle from a curarized frog, 

 avoiding all injury to the muscle. Place the 

 muscle in the trough, and cover it with normal 

 saline solution. Bring a non-polarizable elec- 

 trode against the centre of each long side, so 

 that the current, lines shall cut the muscle 

 fibres at right angles. Close the key. 



There will be no contraction. The muscle is 

 inexcitable to currents that cross its fibres at 

 right angles. 



