1915] SPOEHR—RESPIRATORY ACTIVITY 369 
Methods and apparatus 
In fig. x the apparatus used in this investigation is schematically 
shown; all of the tubes are of glass with heavy rubber connections. 
In order to avoid all possible contamination of the air, this was 
drawn from out-of-doors on the north side of the laboratory building, 
through a glass tube, and entered the apparatus at £,. The air 
was not drawn through any liquid in order to avoid submitting 
the plants to changes of pressure, and so as not to affect the elec- 
trical conditions of the atmosphere. The large bottle (B) con- 
tained a 50 per cent aqueous solution of potassium hydroxide; the 
glass tube was placed so that the air passed immediately over the 
solution. This bottle was omitted in the experiments of short dura- 
tion. In order to further remove the carbon dioxide, the air was 
passed through the bulb tubes (C); the lower portion of the bulbs 
were filled with 50 per cent potassium hydroxide solution. The 
tubes were so arranged that they could be shaken from time to 
time. S represents a glass tube, one inch in diameter, containing 
coarse soda lime (4 mesh). The air then passed into a Frease 
electrical thermostat (J). This was kept at 29° in all of the experi- 
ments given below. It was, of course, of great importance that the 
air coming in contact with the plants should also attain the same 
constant temperature. In order to do this, the air was first passed 
into a 500 cc. Erlenmeyer flask (F), then through 45 feet of thin- 
walled glass tubing (G), and finally into the flask R containing the 
plants. As there was always a small amount of water carried out 
with the air current, this was condensed and trapped at W. The 
rate at which the air was allowed to pass through the entire appa- 
ratus was controlled by means of the glass stopcock A. It was 
found that variations in the rate of air from 0.5 to 8 liters per hour 
caused no difference in the rate of carbon dioxide evolution. P, 
and P, represent three-way glass stopcocks, by means of which the 
course of the air could be changed from one to the other of the 
Meyer’s tubes (M) without interrupting the experiment. The 
Meyer’s tubes were found far more satisfactory for the absorption 
of carbon dioxide than Pettenkofer tubes or any of the modifica- 
tions of the latter. Especially was this true in the experiments 
