MECHANICAL EFFICIENCY OF THE HUMAN BODY 113 
the maintenance of the body of a subject lying quietly during a period of 
time equal in length to the working period. A value, which may be termed the 
"net efficiency" or "pure efficiency," would thus be obtained by the formula 
ax 100 2 
, in which a is the external amount of muscular work performed, 6 
b—c 
the total calorie output for the period during which work was performed, and 
c the resting requirement in calories during a similar period. Under these 
conditions, therefore, the value b—c represents the increment in oxygen or 
calories required to produce a calories of external muscular work. 
METHODS OF COMPUTING THE NET EFFICIENCY. 
This relationship has been used by many writers in their computations, 
but we find that there are many methods for computing this net efficiency. 
For instance, Durig ° has emphasized the fact that when computing the net 
efficiency for a person walking along level ground, it is a question whether 
the resting lying metabolism should be deducted, or the metabolism while the 
person is standing. Similarly, for walking up an incline or climbing moun- 
tains it is difficult to select the exact base-line for comparison. In the work 
of mountain climbing, which has been studied so extensively by Zuntz, 
Durig, and their collaborators, it is legitimate to deduct not only the meta- 
bolism when the subject is lying quietly awake, but also logical to deduct the 
metabolism incidental to movement along a horizontal plane for a distance 
equivalent to that traveled on an ascent less the height; the actual amount 
of work involved in raising the body to a vertical height will then be shown 
by the increase in the oxygen consumption during the ascent over that 
required to move the body forward on the horizontal plane. This method of 
computation has been employed quite extensively. In the computations of 
the results of his mountain-climbing experiments, Durig has first deducted 
from the total katabolism the metabolism of the subject while lying quietly 
and then from the value remaining he has computed that for the "horizontal 
component;" deducting this, he obtains the value for the katabolism due to 
raising the body to a given height, i. e., the "vertical component." The 
difficulties incidental to this form of computation need not be pointed out. 
Although somewhat extraneous to this discussion, it is not without inter- 
est to note that Durig states in his conclusions b that experiments of this kind 
should be made in a respiration chamber since the Zuntz method does not 
take account of the cutaneous respiration and makes no provision for eliminat- 
ing the influence of the resistance to the work of respiration. While the form 
of respiration apparatus used in the present series of experiments does not 
measure the cutaneous respiration, which is unquestionably considerable, 
yet, on the other hand, it does eliminate all resistance to the respiration since 
there are no valves to be actuated and no meter to be turned. A special 
calorimeter for severe muscular work is in process of construction in this labo- 
atory which will give an opportunity for measuring the cutaneous respiration, 
but the results of this research may be taken as representing an intermediate 
step between results obtained by the Zuntz method and by the respiration 
chamber. 
■ Durig, Physiologische Ergebnisse Monte Rosa Expedition, Ueber den Gaswechsel beim Gehen, Denk- 
schrift d. math.-natur. Klasse d. Kaiserl. Akad. d. Wias., Wien. 1909, 86, p. 294. 
» Durig, loc. tit., p. 338. 
