CALIBRATION SCALE FOR BREAK SHOCKS 57 
lightly upon a smoked drum. The minimal contraction 
could be detected without difficulty, since the whole appa- 
ratus was made rigid enough for the slightest movement 
of the muscle to show itself at the end of the lever. 
Connection between the muscle and the terminals of the 
secondary coil was by means of two platinum needles 
soldered to fine copper wires leading from the secondary 
terminals. These needles were thrust directly through 
the muscle tissue, one about 5 mm. below its origin, 
the other the same distance above the distal tendon, 
both in the same vertical plane. By this method of 
connecting the muscle, variations in the secondary re- 
sistance aside from those in the tissue itself were avoided. 
At least half an hour was allowed to elapse after the 
muscle was hung in position before stimulation was 
begun; in order that summation might not enter, the 
shortest interval allowed between successive stimuli was 
ten seconds; to avoid fatigue the strength of stimulus 
used was always kept as near minimal as possible. The 
results of repeated experiments show that under these 
conditions a high degree of constancy is usually main- 
tained during the interval, about three hours, required 
for a single experiment. That each experiment be com- 
plete in itself is, of course, necessary, since no means has 
suggested itself for obtaining a response which shall 
remain constant through a period of successive days. 
To have conditions uniform the electrode nearer to the 
