126 



ELECTRO-PHYSIOLOGY 



('HAP. 



provided only that the increment accrues gradually and evenly. 

 The same thing is, as we have said, still more easily established 

 in muscle. 



If the action of make and break induction currents is 

 investigated in the nerve-muscle preparations of other animals, 

 very different results are arrived at (as recently pointed out by 

 Schott, 13), showing once more how unjustifiable it is to lay too 

 much stress on facts derived from experiments with one kind of 

 animal. 



In the nerve-muscle preparation of toads Schott (13) found 

 the steeper break induction shocks relatively less effective than in 



FIG. 178. Toad's gastrocnemius. a, Make induction twitch ; b, break induction twitch. 



(J. Schott.) 



the frog ; there is hardly any difference in the distance of coil at 

 which the make and break shocks take effect. While the in- 

 directly excited frog's muscle always describes much higher 

 twitches (of medium size) if break shocks are employed, this is 

 not the case with the toad, and the make shocks may even be 

 the more effective (Fig. 178). According to Griitzner (14), single 

 induction shocks of different time-distribution can also be produced 

 as follows. A ring of sheet-iron is fastened to a brass disc in 

 the form of Fig. 179. This consists of two parts, M and N, of 

 which the latter (on rotating the disc to the right) rises gradually 

 from its base H upon the brass-plate to its greatest height, while 

 M is cut off in the direction of the radius of the disc. If the 

 ringed iron piece MN is then rotated between the poles of a 

 horse -shoe magnet, surrounded with wire -coils, there will (on 

 turning the disc to the right) be a constantly increasing part of 



