DESCRIPTION OF APPARATUS. 



35 



by Zuntz and his co-workers that a subject may be trained in a rela- 

 tively short time to carry such an apparatus successfully; nevertheless 

 its transportation is at best difficult, and the method is more fitted for 

 studies of that type of walking in which loads would normally be carried 

 upon the back. Both Zuntz and Durig have shown that they recognize 

 this fact, as they have made studies in which the gas-meter was not 

 carried by the subject, and the walking was done upon a treadmill. 



Several years previous to our research, Mr. E. H. Metcalf, then a 

 member of the staff of the Nutrition Laboratory, designed a tread- 

 mill and had it constructed under his supervision in the machine-shop 

 of the Laboratory. This treadmill was used for the first time in the 

 research carried out in 1913-14 and the fact that it satisfactorily sus- 

 tained a severe test at this time testifies to the designing ability of Mr. 

 Metcalf and the constructive skill of Mr. W. E. Collins, the mechan- 

 ician of the Laboratory. A general view of the treadmill and its dispo- 

 sition with regard to the other apparatus is shown in figure 1. A more 

 detailed perspective drawing is given in figure 3. 



FIG. 3. Treadmill designed by E. H. Metcalf. 



The endless leather belt travels over two wooden pulleys A and B, the actuating mechanism 

 being an electric motor. The tension on the belt may be adjusted by the bolt and nut C. 

 A revolution counter is shown at R. 



The treadmill is provided with an endless belt, 60 cm. wide, 435 

 cm. long, and approximately 10 mm. thick. This belt travels over 

 two wooden pulleys, A and B, having a width of 60 cm. and a 

 diameter of 41 cm. The pulleys are supported on ball bearings at the 

 ends of a wooden frame. On the rear pulley is attached a sprocket- 

 wheel, which connects with the reducing-gear actuated by a one-half 

 horsepower electric motor. The tension on the belt may be easily 

 adjusted by means of the screw C, thus preventing the belt from slip- 

 ping. To support the belt between the pulleys and provide a surface 

 for the man to walk upon, steel tubes, 46 in number, with an external 

 diameter of 25 mm. and a length of 61 cm., are set into a steel frame- 

 work, the distance between the centers of the tubes being 27 mm. 

 These steel tubes are fitted at each end with annular steel ball bearings. 



