TECHNIQUE FOR METABOLISM DURING WORK. 



127 



diameter. The belt is 435 cm. long and the portion on which the sub- 

 ject walks is supported by steel tube rollers with ball bearings. 



The mill was driven by a 220-volt, D. C, | H. P. motor (D) placed in 

 front of the rear pulley, to which it was connected by a chain drive and 

 reducing gears. The line to the motor entered the chamber between 

 the base and skirt by being bent U -shape to conform to the trough of 

 the base. Two variable resistances were inserted in the line at the 

 observer's table for regulating the speed of the mill. 



In order to have the experiments with the different subjects as com- 

 parable as possible, it was necessary to have the speed at which the sub- 

 ject was walking under constant observation and control. In previous 

 experimenting a measure of the 

 speed of the treadmill was ob- 

 tained by means of a mechani- 

 cal counter which recorded the 

 revolutions of the front pulley 

 of the treadmill. As the tread- 

 mill in this research was in- 

 closed in a chamber, it became 

 necessary by an electrical de- 

 vice to transmit these revolu- 

 tions to a counter which could 

 be under constant observation. 

 This was done by attaching to 

 the periphery of the front pul- 

 ley a brass segment which 

 made a wipe contact with a 

 laminated brass finger fastened 

 to the frame of the mill. With 

 each revolution of the pulley an electric contact was made which actu- 

 ated a counter placed on the observer's table and known in the tele- 

 phone trade as a "p. b. x. message register." (See fig. 15.) As a 

 precaution two such contacts and counters were installed and con- 

 nected by a double-throw switch. In practice, however, no difficulty 

 was experienced and only one counter was used. 



To test the speed of the mill the time required for 10 revolutions of 

 the pulley as recorded by the counter was noted with a stop watch, and 

 by reference to a previously prepared chart the speed was immediately 

 known. After the proper rate was estabhshed, which rarely occupied 

 over a minute, further observations were taken every 2 minutes, and 

 any adjustment that seemed necessary was easily and quickly made by 

 the adjustable resistance. As a rule very little adjusting had to be 

 done after the first 2 minutes and the speed was very constant. With 

 uniformity of speed there was naturally uniformity in the distance 



Fig. 15. — Electrical counter. 



The message register is shown mounted in a specially 

 designed support which places it conveniently for 

 reading. 



