

INVESTIGATIONS ON METABOLISM. gI 

of specially devised air pumps, its total current was measured 
by a gas meter especially constructed for the purpose, the sam- 
ples of incoming and outgoing air were drawn by aspirators, the 
carbon dioxide in the sample was determined by absorption by 
soda lime, and the water by absorption by sulphuric acid. ‘The 
volume of air passing through the apparatus varied from 50 
to 75 liters per minute. The longest experiment was of 12 days 
duration, and was made with an air current of approximately 
55 liters per minute. It is desirable to have the incoming cur- 
rent of air as dry as possible. ‘This drying was easily accom- 
plished by surrounding a portion of the pipe through which it 
passed with a freezing mixture of salt and ice. 
The samples of air for analysis were drawn by means of 
aspirators, two of which had previously served for the calibra- 
tion of the meter. ‘These aspirators, three in number, are 
cylinders of galvanized iron, standing upright, with conical 
ends. The cylinders are 56 cm. (22 in.) in diameter and 46 cm. 
(18 in.) in height, exclusive of cones which form the ends. 
To fill the aspirators the water is introduced near the top while 
the air passes out from the upper neck. In drawing the sam- 
ples of air the water passes out from the lower while the air to 
be measured enters the upper neck. Horizontal tubes connect 
the two necks with an upright glass tube on the side of the 
aspirator. ‘This serves as a gauge and shows the height of the 
water. It is accurately marked at the top and bottom and 
thus permits the drawing off of a definite quantity of water 
and consequently the accurate measurement of the volume. 
In taking a sample the aspirator is first filled to the mark indi- 
cated on the water gauge outside, the connection is then made 
by a 3-way cock with the tube through which the sample of 
air is drawn from the main current. 
APPARATUS FOR DETERMINING THE CARBON DIOXIDE AND 
WADEHR IN SAMPLHS OF AIK. 
The constituents of the air determined in the experiments 
described beyond were carbon dioxide and aqueous vapor. 
The determinations are made by absorbents, soda lime for 
the former and sulphuric acid for the latter. These re- 
agents are contained in ordinary glass U tubes. The device 
above referred to for removing the moisture from the main 
