TECHNIQUE FOR METABOLISM DURING WORK. 129 
within the chamber that a marked stimulus to the pulse or respiration 
would be produced. 
THE STEP RECORDER. 
A record of the steps taken during walking was obtained by a small 
electrical contact device at the rear of the treadmill to which the sub- 
ject's left foot was attached by a long coil spring. The spring had 
sufficient tension to operate the contact when the foot was thrown for- 
ward, but at the same time was so weak that it was not noticeable to 
the subject as he walked. The electric contact operated a message reg- 
ister, also a signal magnet placed before the camera which was used in 
connection with the string galvanometer for the pulse records. By the 
latter, photographic records showing the steps were secured on the same 
paper with the electrocardiograms which were taken at the close of the 
first, sixth, twelfth, and twenty-fourth minutes of walking. A specimen 
record is shown in figure 16 with the pulse records. 
There was an occasional chatter of the signal magnet due to a re- 
bound by the coil spring. This chatter is in most cases evident in the 
spacing on the records and such irregular movements of the signal 
magnet are neglected in the counting. From these records is found the 
number of steps per minute at the time of the observations and the 
average of these is used as the steps per minute for the period. 
PULSE-RATE. 
In order to secure pulse records while the subjects were walking, 
leads from the string galvanometer in the psychological laboratory were 
carried to the room where the treadmill was situated and entered the 
chamber through the hard-rubber plug in the front of the cover (see P, 
fig. 14). The leads terminated inside the chamber in a receptacle 
into which the subject plugged the terminals of the body electrodes 
after he entered the chamber. These electrodes were the same as those 
used in securing electrocardiograms during short periods of muscular 
exertion. They are shown in figure 26 and described on page 153. 
Since there was always a certain amount of electrical leakage from 
the treadmill motor, as well as static electricity of the leather belt, it 
was necessary to protect the string of the galvanometer from these 
stray charges which interfered with the electrocardiograms as well as 
endangered the safety of the string itself. This was successfully done 
by grounding the subject by means of the third electrode, G in figure 
26, worn on the lower chest and connected to an iron water-pipe outside 
the chamber. This arrangement had previously been found more 
satisfactory than grounding the treadmill or the string galvanometer 
and made it possible for the men to walk in ordinary shoes Without 
further insulation. 
A short branch line connected by a double-pole double-throw switch, 
easily accessible to the operator, allowed either the subject walking on 
