126 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



From a knowledge of the volume of the chamber and the percentage 

 composition of the air at the beginning and end of the experiment, it 

 was possible to calculate the total amount of carbon dioxide produced 

 during the period of walking, and, from the time involved, the produc- 

 tion per minute. In the same manner the percentage of oxygen at 

 the beginning and end would give the amount of oxygen consumed on 

 the per minute basis. From the gaseous exchange thus secured, the 

 respiratory quotient was obtained and the heat produced was calcu- 

 lated by indirect calorimetry. The detailed method of the calculations 

 and certain corrections required are given on page 134. 



MEASUREMENT OF WORK PERFORMED DURING WALKING. 



In the experiments in which the subject walked upon the treadmill, 

 the distance walked and the rate of walking were recorded, also the 

 number of steps taken. The body-weight and other characteristics of 

 the men were likewise taken into account. In this research it was 

 found impracticable to complicate the apparatus by adding the device 

 employed by Dr. Carl Tigerstedt^ to indicate the up-and-down motion 

 of the body while walking. 



It must be remembered that in these experiments the subject was 

 walking in an inclosed chamber and was thus inaccessible to the oper- 

 ators during the experimental period. Although the small circular 

 window gave the man an opportunity to look out, it did not provide 

 sufficient light to allow the operators to make observations of condi- 

 tions within the chamber, and all recording devices therefore had to be 

 outside the chamber proper. Furthermore, the chamber had to be 

 air-tight, which required extra precaution in its construction and lim- 

 ited in a large measure the manner by which these recording devices 

 could be attached. 



The treadmill used was designed by Mr. E. H. Metcalf, formerly of 

 the Nutrition Laboratory staff, and has been described in detail else- 

 where.^ It has proved most satisfactory and can be adjusted to prac- 

 tically any degree of speed. It has been the experience of subjects 

 walking upon this treadmill that it represents very closely free walking 

 upon a smooth sidewalk. To eliminate the element of novelty, the 

 subjects were given 5-minute periods of walking beginning Nov. 10, 

 every time they came to Boston, so that when the final quantitative 

 test was made, the men would be thoroughly familiar with the appa- 

 ratus and its technique. 



The treadmill, with connections and accessories, is shown in figure 

 14 in its location in the chamber. Briefly, the treadmill consists of a 

 leather belt 58 cm. wide passing around two wooden pulleys 41 cm. in 



^ Reported by Benedict and Murschhauser, Carnegie Inst. Wash. Pub. No. 231, 1915, p. 39. 

 * Benedict and Murschhauser, Carnegie Inst. Wash. Pub. No. 231, 1915, p. 34. 



