METHODS AND APPARATUS 
27 
of the motor, and the voltage between these points, the amount of work re- 
quired to rotate the machine could be com- 
puted. It was hoped by this means to 
devise some simple and rapid method for 
calibrating the machine without using the 
more expensive method of determining the 
heat produced by the respiration calorim- 
eter. Owing to the great loss by friction 
and the tension of the belt, the prelimi- 
nary experimenting by this method was very 
unsatisfactory, and time did not permit 
further study along this line. The electric 
motor was, however, extensively used to 
drive the ergometer in the so-called "motor- 
driven experiments." 
It is important to note that the er- 
gometer, when once calibrated, gives di- 
rectly the number of calories of external 
muscular work put upon the machine for 
each revolution of the pedals, the calories 
varying somewhat with the rate of speed 
of revolution. Fortunately for the speeds 
most commonly used by bicycle riders, 
namely, between 60 and 80 revolutions of 
the pedals per minute, when the magneti- 
zing current is constant, the energy output 
per revolution is practically constant. At 
speeds lower or higher than this, there is a 
marked decrease in the heat per revolu- 
tion. The peculiar anomalies of these calibration curves have been the 
subject of special discussion elsewhere." 
ri.SC 
AMP 
'OS 
4JV« 
*izs 
AMP 
',.,0 
A*r 
y^Ti 
AMP 
SO 
«m 
30 40 50 60 70 
90 100 110 120 130 
Fig. 1. — Calibration curves showing 
heat per revolution of ergometer II. 
The revolutions per minute are given at the 
bottom of the figure, and the calories per 
revolution at the left-hand margin. 
APPARATUS FOR DETERMINING THE GASEOUS EXCHANGE. 
A respiration apparatus that would at one and the same time provide 
sufficient ventilation for a man working almost to the limit of human endur- 
ance and permit both the complete absorption of carbon dioxide and an 
accurate measurement of oxygen was difficult to obtain, but by slightly 
modifying the form of respiration apparatus employed in this laboratory for 
a number of years we were able to meet the requirements for experiments with 
muscular work. This apparatus has recently been described in detail, in- 
cluding the modifications necessary for experiments with muscular work, 6 
together with a diagram showing the particular adjustment of the apparatus 
for such experiments. Since the description was published, however, further 
modifications were found desirable in the progress of this research. 
The connections of the respiration apparatus as used for muscular-work 
experiments are shown in fig. 2. As may be seen in this figure, a rotating 
ventilator or blower draws air along a pipe and forces it through two Woulff 
a Benedict and Cady, loc. cit.; Cady and Benedict, loc. cit. 
b Benedict, Deutsch. Archiv. f. klin. Med., 1912, 107, p. 156. 
