104 
Journal of Agricultural Research 
Vol. XXXII, No. 3 
the principle of the compensating chamber to avoid the necessity of 
correcting for barometric and temperature changes. It is said to be 
sensitive enough to follow the oxygen absorption by a single insect egg 
weighing 2 mgm. in io-hour periods. Krogh also described a later modi¬ 
fication of Winterstein’s apparatus which he says can be made even more 
sensitive than the Krogh apparatus. 
Very recently, Lund (16) has developed a very simple apparatus for 
following the C 0 2 production by small objects by titration of baryta water. 
With proper manipulation, it is very sensitive, but, like the other purely 
chemical methods, Lund’s method requires special care to avoid errors 
due to the absorption of C 0 2 from sources other than the respiring 
material, or errors from other sources. It also neglects oxygen con¬ 
sumption. 
The range of some of the apparatuses of the micro type is sufficient to 
adapt them for much of the work on the respiration of seeds, but none of 
them provides for simultaneous determination of both sides of the 
respiratory exchange in the same material. 
(5) INDICATOR METHODS 
Doctor Haas (8) and Professor Osterhout (17) recently perfected an in¬ 
dicator method which is very sensitive in detecting small quantities of C 0 3 
respired. Their method is especially adapted for use in investigations 
in which only the comparative rate of production of C 0 2 under different 
conditions is to be studied. It has the advantage of sufficient sensitive¬ 
ness so that the experimental time can be very short, a matter frequently 
of prime importance; and the small amount of time required for the 
manipulation of the apparatus adapts the method for rapid and simul¬ 
taneous determinations in several different experiments. By means of 
special calibrations and a sampling device the apparatus can be used for 
the approximate determination of the absolute amounts of oxygen 
absorbed and C 0 2 produced; but this is not its special use. Indicator 
methods for the determination of the oxygen absorbed by the respiring 
material have also been described by Osterhout (18) and by Harvey (10), 
but these present certain grave objections and at best are not available 
for simultaneous determination of the C0 2 produced. The use of the 
indicator method for accurate measurement even of C0 2 output requires 
constant care to avoid errors due to buffer effects (19) or to the possible 
production of acid-reacting substances other than C 0 2 or of alkaline- 
reacting substances. 
In view of the limitations of the apparatuses previously used in inves¬ 
tigations of respiration, we undertook to develop a new apparatus which 
would be simple, easy to use, and free from as many as possible of the 
objections which other apparatuses presented. With our apparatus, as 
described on the following pages, oxygen consumption and C 0 2 produc¬ 
tion are determined in the same apparatus and for the same period of 
time, using the whole volume of air instead of a sample. Both sides of 
the respiratory exchanges are therefore followed in identical material 
and without multiplication of experimental errors. The gaseous ex¬ 
changes are determined at the end of an experimental period by means 
of a manometer, which is an integral part of the apparatus, somewhat 
on the plan of BunzeU’s oxidase apparatus (4). Since the C 0 2 given off 
by the respiring material accumulates and tends to compensate for the 
oxygen absorbed by it no large changes in pressure occur during any 
