128 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



traveled during the periods, but there was always the possibility that 

 on account of poor contact the counter might fail to register or that an 

 occasional chatter of the contact might cause an extra number to be 

 recorded. 



To guard against this possibility, advantage was taken of the con- 

 struction of the message registers which allowed the connection of a 

 second circuit. This second circuit was carried to a signal magnet and 

 a Blix-Sandstrom kymograph. With each operation of the message 

 register this separate circuit was also completed through the signal 

 magnet. As the kymograph was uniform in its movement, any skip 

 or extra count in the message register would at once be apparent in the 

 spacing of the signal magnet tracings on the kymograph. The records 

 show no such irregularities and the numbers read off the message regis- 

 ters are believed to be accurate for the revolutions of the pulley. The 

 counter was read at the beginning and end of a period. From these 

 records and from the circumference of the pulley and the length of 

 the experimental period, computations could be made of the total 

 distance traveled and the rate per minute. 



Factors which have to be considered when comparing the metabo- 

 lism of different individuals during horizontal walking include the 

 weight moved and the distance traveled in unit time. 



It has been shown^ that the energy expended during horizontal walk- 

 ing when calculated on a basis of kilogram weight and meter distance 

 increases very slightly with the rate of walking up to a point of approxi- 

 mately 80 to 85 meters per minute. This point has been termed the 

 "speed of maximum efficiency." At this point there appears to be a 

 break in the curve and any increase in speed is done at a relatively 

 greater cost in energy expended. Brezina and Kolmer^ have shown 

 that within this optimum range of speed the metabolism per kilogram 

 and meter distance is independent of the weight carried up to a load 

 of 20 kg. 



It was desirable, then, to maintain a rate of walking within this 

 optimum limit and a rate of 70 meters per minute was selected. This 

 is a fair rate of walking and does not in 20 to 25 minutes introduce tha 

 element of fatigue. This rate was also convenient because the amount 

 of carbon dioxide eliminated during the time available for the experi- 

 ment, judging from other data, would in all probability not exceed 1 per 

 cent of the chamber volume. The capacity of the Haldane gas-analysis 

 apparatus used for the carbon-dioxide determinations was 1 per cent, 

 as previously stated, and it was desired to use this small apparatus 

 rather than other larger and more complicated forms. Furthermore 

 it was desirable not to have so great a concentration of carbon dioxide 



^ Durig, Denkschrift. d. math.-natur. Kl. d. kaiserl. Akad. d. Wissenschaften, 1909, 86; also 



Benedict and Murschhauser, Carnegie last. Wash. Pub. No. 231, 1915, p. 85. 

 * Brezina and Kolmer, Biochem. Zeitschr., 1912, 38, p. 142. 



