Chittenden and Cummins— Gas Metabolism. 407 
two of which had a capacity of 15 litres and one of 74 litres. The 
three aspirators working together would therefore draw through the 
chamber 374 litres of air at every filling, and the flow was so regulated 
that 30 minutes were required to draw that amount of air through 
the apparatus. The flow of water from the aspirators was quite regu- 
lar, since the inlet tubes went to the bottom and the air had to 
bubble up through the water, as the latter ran out, on the principle 
of Mariotte’s bottle. The rate of flow was regulated by carefully 
changing the difference in height between the inlet tube (for air) of 
the aspirator and the outlet tube (for water). This of course, at the 
outset, was a tedious operation, but when once perfected and the 
apparatus permanently set up, the three aspirators ran exactly to- 
gether, with a maximum variation of 15 seconds for the half-hour, 
which variation, however, was seldom observed. In addition, each 
aspirator was marked off into eight divisions, the last one of which 
was equal to only one-half of the others. In the two large aspirators 
these divisions indicated exactly the same volume, while in the small 
aspirator the divisions represented half the capacity of the former ; 
but the flow of water in the latter was regulated to consume the 
same amount of time as in the former. Hence four minutes were 
required for the water to flow by each of the first seven divisions, 
and two minutes for the last, making a total of thirty minutes for the 
entire volume of water to flow from each aspirator. 
The tube drawing the respired air from the chamber in which the 
animal was enclosed, was divided a short distance from the chamber, 
as seen in the figure, and two-fifths of the mixed air was drawn 
successively through three absorption tubes filled with a standard 
solution of barium hydroxide for absorption of the carbonic acid. 
The absorption tubes were about two-thirds of a metre long and the 
lower tube (a) contained 100 ¢. c. of a standard baryta solution, the 
middle tube (0) also 100 ¢. ¢. of the solution, and the upper tube (c) 
50¢.¢. The amount of carbonic acid absorbed was, at the end of the 
experiment, determined by titration with a standard solution of oxalic 
acid, using phenol-thalein as an indicator. Two titrations were made, 
one of the contents of tube @ and one of the contents of the two tubes 
6 and e«. By using the three tubes, absorption of the carbonic 
acid was quite complete. In order to aid absorption, the air was 
broken into small bubbles by being forced through a small tube dip- 
ping beneath the barium hydroxide. Frequent blank experiments 
showed that all of the connections were perfectly tight, and further, 
all of the tubes being in the same position, that the flow of water 
