28 
MUSCULAR WORK 
bottles containing sulphuric acid. The greater part of the water-vapor in the 
air-current is absorbed by the acid in the first bottle, but any traces which 
may remain are re- 
moved by the acid 
in the second bottle. 
The dry air is then 
passed through the 
carbon-dioxide ab- 
sorbers, i. e., two bot- 
tles containing soda- 
lime. Since the air 
absorbs water from 
the soda-lime it is 
necessary to remove 
this moisture by pass- 
ing the air-current 
again through sul- 
phuric acid. When 
the air leaves the 
drying-bottle it is de- 
ficient in oxygen and 
H 2 S04. 
/i 2 S0+ 
Fig. 2. — Schematic outline of the respiration apparatus. 
free from carbon dioxide and water-vapor, but inasmuch as perfectly dry air, 
if inspired by the subject, would absorb moisture from the respiratory tract 
and produce discomfort, moisture must be added to the air before it is re- 
turned to the subject for breathing. This is done by passing the air-current 
through the lower part of a Kipp generator partially filled with water. A 
small amount of sodium carbonate is added to the water in this vessel, which 
effectually absorbs any acid fumes that may have been carried over. The 
deficiency • in the oxygen content is made up by the addition of a measured 
amount of the gas at O2. The air then passes through a 3-way valve 
and returns, either directly or through the short circuit connected with 
the subject, to the tension-equalizer and the blower. By weighing the carbon- 
dioxide absorbers, and the air-drying vessel before and after the experimental 
period, and noting the amount of oxygen consumed either by finding the loss 
in weight of the cylinder of oxygen, or by measuring with a carefully calibrated 
gas-meter the volume of oxygen added to the air-circuit, the carbon-dioxide 
production, the oxygen consumption, and the respiratory quotient may be 
computed. 
The absorbing system as here described and used in the muscular-work 
experiments differs from the usual adjustment of the apparatus in several 
particulars. When the subject is engaged in severe muscular work, an ex- 
cessive amount of carbon dioxide is produced, sometimes amounting to as 
much as 2,500 c.c. per minute. To provide for the absorption of this large 
amount of carbon dioxide, it was considered safer to use two soda-lime 
bottles connected in series, instead of one carbon-dioxide absorber as usual. 
In the most recent form of the respiration apparatus a spirometer b is 
used, and much emphasis is placed upon the character of the respiration as 
a As a matter of fact, to guard against oxygen-want in the apparatus, the air in the closed system was always 
arbitrarily adjusted somewhat oxygen-rich. 
6 Benedict, Deutsch. Archiv. f. klin. Med., 1912, 107, p. 172. 
