TETANUS 



31 



Shift the oscillating rod in the clamp supporting it, so 

 as to allow its full length to oscillate, and adjust its 

 height so that the pointer just touches the mercury 

 when at rest. Open the key in the secondary circuit 

 and, by moving the oscillating rod in and out of the 

 mercury by hand and shifting the distance of the 

 secondary coil from the primary, determine the, position 

 of the coil at which contractions are only obtained at 



Fig. 13. 



break. If such a position cannot be clearly obtained, 

 reverse the connection of the wires of the secondary coil 

 and try again. Set the drum running at a rather slow 

 velocity (about 6 cm. per sec.), put the rod into oscilla- 

 tion, then open the key in the secondary circuit for 

 about 5 seconds and close it again. Stop the drum, 

 shorten the rod in its clamp by about 4 centimetres, ad- 

 just it to the mercury level, and take another tracing of 



