484 APPENDIX 



on breaking or opening the current at the anode (A.O.). Von Bezold 

 first demonstrated this after experiments by Schiff more than fifty years 

 ago. Still no explanation worthy of the name is forthcoming, and the 

 best that can be said, apparently, is that when the current is applied 

 ("make"), the muscles' irritability is increased at the cathode more than 

 at the anode, and so the contraction starts powerfully at the former pole; 

 while when the current is removed ("break"), the irritability is greater 

 at the anode than at the cathode (but less than at the cathode on making). 

 When we have learned the facts about the nervous impulse and muscular 

 contraction these "explanations" may seem less pedantic and more use- 

 ful than at present. 



See also Expts. 59, 60, and 80, the phenomena being essentially the 

 same in nerve as in muscle. 



Expt. 39. Induced Electricity as a Stimulus. Insert the inductorium 

 arranged for single shocks in place of the rheocord of the last experiment. 

 Draw or turn the secondary coil far enough away from the primary so 

 that a make-shock on closing the simple key will just not cause a contrac- 

 tion. Hold the key closed and meanwhile observe that no contraction 

 occurs during the passage of the galvanic current through the primary 

 coil, for induced electric currents are always of only momentary duration. 



Open the simple key. Contraction then occurs, demonstrating that 

 the induced break-shock is a stronger stimulus than the induced make- 

 shock. This excess is due to the absence from the break of the "extra- 

 currents" which make less sudden the make-shock (as demonstrated 

 previously). Repeat with various strengths of induced electricity, and 

 see, and feel on the tongue, that the break is a much stronger stimulus 

 than is the make; the opposite is true with the simple galvanic current. 



The extra-currents referred to as the cause of the lessened stimulating 

 effect of the make-shock are inductively generated in contiguous rounds 

 of the wire of the primary coil of the inductorium, just as induced cur- 

 rents are generated between the rounds of the primary and the secondary 

 coils. These currents are in direction opposite to the regular currents, 

 and it is their opposition that makes the rise to full strength of the regular 

 current gradual instead of sudden. (See Expt. 44.) As regards the break 

 of the regular induced current (a stronger stimulus than the make) : 

 when the primary current is shut off both the regular current and the 

 extra current cease at once, and the suddenness of the change of strength 

 of stimulus is maximal, greater than in case of the make, and so stimulates 

 more strongly. 



Expt. 40. Duration of Stimulus Affects Contraction. (Apparatus: 

 Myograph, inductorium, commutator without cross-wires, two cells, 

 sartorius.) Attach one cell to the inductorium for single break-shocks 

 and connect the secondary coil with the two posts of one side of the 

 commutator. Connect the other cell directly with the posts of the 

 opposite side of commutator. Connect the rocker of the commutator 

 with the sartorius myograph in the usual way. Have the drum rotate 

 at its maximum gear-speed. Write an abscissa line. Send a maximal 

 break induction-shock through the muscle. Lower the drum and write 



