408  Ohittenden and Cummins—Influence of Some Organic 
from each aspirator was perfectly uniform, and that the aspirators 
could be relied upon to draw the given volume of air through the 
apparatus in the time designated without any appreciable variation. 
In addition, the two-fifths drawn through the absorption tubes for 
determination of the carbonic acid was always exactly two-fifths of the 
aspirated air; since the aspirators, as already remarked, worked with 
perfect uniformity. Any tendency to variation, either in the time, 
or in the action of the individual aspirators, was noticed at the 
very outset of the experiment, as the water reached the level of the 
different marks on the aspirators, and could be at once checked or 
controlled by moving slightly the water outlet tube so as to either 
increase or diminish the difference in height between the latter and 
the inlet tube for air. Theoretically, variations in the temperature of 
the water in the aspirators might affect somewhat the volume of air 
analyzed, but a constant determination of the temperature of the 
water showed such slight variations that they did not seem to justify 
us in making any corrections for possible change in the amount of air 
aspirated. Naturally, all of the supports for the three absorption 
tubes were permanently placed, so that there could be no change of 
position; the tubes themselves placed in the same position in the 
holders; the volumes of baryta solution invariably the same, so as not 
to increase or decrease the pressure to be overcome; and lastly the 
aspirator tubes and stoppers fastened so as not to admit of any change. 
With these precautions, the results obtained, both as to the volume 
aspirated and the time consumed, were quite satisfactory. ; 
As already mentioned, the total capacity of the three aspirators 
was 874 litres or 54 litres more than the capacity of the bell jar. 
This amount of air drawn through the chamber in 30 minutes, was 
more than enough to supply the largest rabbit experimented on, with 
the necessary amount of oxygen. But there must have been a slight 
accumulation of carbonic acid in the air of the chamber; this, how- 
ever, was a constant factor throughout the experiments. Further, 
the results obtained, expressed in milligrams of CO,, do not represent 
the total amount of carbonic acid eliminated by the rabbit during 
the thirty minutes of the experiment, but simply the amount of CO, 
contained in the 374 litres of air aspirated during that time. Such a 
result, however, ought certainly to show just as plainly any influence 
on the elimination of carbonic acid, as a determination of absolute 
quantity and thus be equally valuable as an indication of influence or 
lack of influence on the gas metabolism of the body. Further, the 
results thus obtained ought to express equally as well, the comparative 
action of the various substances experimented with. / 
