72 TEXT-BOOK OF PHYSIOLOGY. 



latter placed on opposite ends of a freshly prepared sartorius muscle 

 of a frog which has been previously curarized, it will be found on 

 closing or making the circuit that the muscle will exhibit a short quick 

 pulsation. During the actual passage of the current, especially if 

 it is weak, there may be no apparent change in the muscle. If the 

 current is strong, the muscle may, on the contrary, remain in a state 

 of continuous contraction. With the opening or breaking of the 

 current the muscle at once relaxes, or perhaps again contracts and 

 then relaxes. The extent of the contraction depends mainly on the 

 strength of the current, being greater with strong, less with weak 

 currents. |[When the current is sufficiently strong to elicit both 

 making and breaking contractions, it is found that the contraction 

 occurring on the make or closure of th^circuit, Js^aJways greater 

 than that occurring on the break or opening of the circuit. |l More- 

 over, it has been shown in many ways that the contraction occur- 

 ring on the closure of the circuit has its origin at the point where 

 the current is leaving the muscle i. e., in the immediate neighbor- 

 hood of the negative pole or cathode and propagates itself to the 

 opposite extremity; while the contraction occurring on the opening 

 of the circuit has its origin at the point where the current is entering 

 the muscle, i. e., in the neighborhood of the positive pole or anodel\ 



The Induced Current. If the primary spiral of the inductormm 

 be connected with an electric cell and the secondary spiral be con- 

 nected with a muscle, it will be found that the current induced in the 

 secondary circuit, both on the make and break of the primary, will 

 also cause the muscle to sharply and rapidly pulsate if the two spirals 

 are sufficiently near each other. Observation, however, makes it 

 evident that the pulsation occurring with the break of the. primary 



f circuit is more energetic than that occurring with the mak& a result 

 the opposite of that obtained with the constant currenw This is 

 not due to any difference in the electricity, however, but to peculiarities 

 in the construction of the inductorium. When the primary circuit 

 is interrupted with sufficient frequency, as it can be by throwing into 

 the circuit Neef 's hammer or some other form of interrupter, the con- 

 tractions excited by the induced currents may be made to succeed one 

 another so rapidly that they become fused together, producing a 

 spasm or tetanus of the muscle. The rapidity with which the induced 

 current appears and disappears, its brief duration, the ease with which 

 its strength can be regulated, combine to render it a most efficient 

 stimulus for either muscle or nerve. 



Conductivity. All muscle protoplasm possesses conductivity. 

 The change excited in a muscle-fiber by the arrival of a nerve impulse 

 is at once conducted with great rapidity in opposite directions to 

 the end of the fiber; the advance of the excitation process is im- 

 mediately succeeded by the contraction process, the change of form 



