METABOLISM WITH GRADE WALKING. 193 



produced; consequently, when metabolism measurements are made 

 after a very brief period of mouthpiece breathing, the respiratory quo- 

 tient would be large. As a matter of fact, under exactly these condi- 

 tions of experimenting, we find a quotient somewhat smaller than 

 those obtained during the tests with a long preliminary period of mouth- 

 piece breathing. No simple explanation for this is at hand. 



These tests have, however, considerable significance in that they 

 indicate the necessity of caution in employing short-period respiration 

 experiments for the computation of the total energy production, 

 especially if the collection of expired air is begun immediately after 

 the mouthpiece is inserted. This is all the more important, since there 

 is an increasing tendency on the part of certain physiologists to utilize 

 the carbon-dioxide exhalation alone as a measure of the metabolism. 1 



When carbon dioxide only is measured during periods of muscular 

 repose, there is nothing in our results to throw any discredit upon the 

 actual determination of carbon dioxide. Indeed, if the respiratory 

 quotient is determined, it seems to be essentially the same, irrespective 

 of the type of respiration. On the other hand, in experiments in which 

 heavy work is performed, and particularly when the mouthpiece is 

 used, and the whole computation of energy is based upon carbon dioxide 

 alone, it is easy to err in selecting the respiratory quotient to be used. 

 To be sure, in many of these tests only an approximate computation of 

 energy is desired. It is important, however, to bear in mind that in 

 this series of comparison tests there is grave doubt of the accuracy of 

 the determination of the respiratory quotient when the period of 

 measurement is preceded by a very short period of preliminary breath- 

 ing through the mouthpiece. 



METABOLISM OF SUBJECTS WALKING ON AN INCLINE. 



In addition to the chronological presentation of the data obtained in 

 the grade- walking experiments in tables 13 to 16, the metabolism 

 measurements have also been assembled in tables 52 to 55, to show 

 the effect of the work performed in the grade walking upon the heat- 

 output in excess of both the standing and the horizontal-walking 

 requirements. These tables show the work performed and the increase 

 in the heat-output. The effect of grade and speed upon the heat-out- 

 put, the physiological factors, and the efficiency is brought out by a 

 summary of the data in table 56. 



In considering the effect of grade walking upon the energy output as 

 presented in tables 52 to 55, it has been assumed that the basal require- 

 ments of the body at rest, i. e., standing, did not alter during the walk- 



t, Miles, Roth, and Smith, Carnegie Inst. Wash. Pub. No. 280, 1919, p. 119, table 5, 

 footnote 2; Benedict and Johnson, Proe. Am. Phil. Soc., 1919, 58, p. 89; Benedict, Collins, Hendry, 

 and Johnson, N. H. College of Agr., Tech. Bull. No. 16, 1920; Waller, Proc. Physiol. Soc., 1918-19, 

 52, pp. xlviii, 1, lix, Ixvii, and Ixxii; 1919, 53, pp. xxiv, xxx, and xliv. 



