28 



METABOLISM DURING WALKING. 



turns the valve connecting the subject with the ventilating circuit. 

 When J is thrown at the beginning of the period, it forces the arm A 

 from its position at stop B over to stop C. This changes the position 

 of the bar D from d to di. In the latter position the button E strikes 

 against D with each revolution of the pulley, this contact operating 

 the counter R. A measurement of the outside circumference of the 

 belt (4.355 meters) and a series of tests showed that one revolution 

 of the pulley was equivalent to 1.328 meters. Hence, from the total 

 number of revolutions of the pulley as recorded by the counter during 

 the period and the equivalent of one revolution of the pulley (1.33 

 meters), the exact distance walked by the subject during the period 

 could be calculated. By readings of the "continuous counter" at 

 the times when the valve is opened and closed, it|is possible to verify 

 the records of the "period counter," so that a check on the record of the 

 distance walked was obtained. 



FIG. 5. Detail of valve-operating device and period counter. 



Valve-operating device. J, bar which, when pushed forward, forces 

 button L from under bar K. The tension of spring M then acts 

 through cord F, operating arm k and valve D in figure 1 (p. 19), 

 connecting subject with the ventilating circuit. (See I, Ik, D, 

 J. L, K, and M, fig. 1, p. 19.) 



Period counter. When the bar A is against the stop B, the pivoted 

 brass bar D is in position d. The brass button E then slides 

 past the bar D without displacing it. When the valve- 

 operating device J is thrown forward, the bar A is pushed 

 against the stop C and the bar D comes into the position di. 

 The button E then strikes the bar D on each revolution of the 

 pulley and the displacement of D operates the counter R, giving 

 a record of the number of revolutions of the front pulley during 

 the experimental period. (See also fig. 1, p. 19.) 



Control of the speed of walking. By means of a stop-watch the time 

 necessary for 10 revolutions of the front pulley as shown by the coun- 

 ter was determined, and then, by reference to a previously prepared 

 table, the speed of the treadmill could be readily obtained. The speed 

 was controlled largely by means of the starting-box, which permitted 

 moderate adjustment. As the experiments progressed, however, there 



