28 ELEMENTARY PHYSIOLOGY. Ill 



making and breaking the current at the mercury contact. Each 

 time the current is made the core of the coil d of the tuning-fork 

 becomes magnetic, the prongs are drawn together and the current 

 broken, the core then ceases to be magnetic and the tuning-fork 

 makes the current again. 



Bring the point of the lever to write on the drum immediately 

 below the tracing. When the lever of the time-marker is oscillating 

 steadily in unison with the tuning-fork (if it does not, adjust the 

 strength of the spring of the time-marker), start the drum and stop 

 after one revolution. An undulating line is traced, each undulation 

 with the tuning-fork given you represents T ^Q of a second. 



Adjust the point of the muscle lever accurately to the commence- 

 ment of the contraction, then press it down and so trace a line down- 

 wards to the time tracing. Shift the lever along the curve and draw 

 lines in the same way from the summit of the contraction, the end 

 of the relaxation, and from the line indicating the moment of stimu- 

 lation. 



DEMONSTRATIONS. 



1. Rate of transmission of nervous impulse. 



2. Rate of transmission of contraction in the sar- 

 torious muscle. 



3. Effect of rate of make and break of the galvanic 

 current. The rheonome. 



