and Inorganic Substances on Gas Metabolism. 409 
In every experiment, the time at which the animal was introduced 
into the bell jar was exactly noted and then two minutes were allowed 
before starting the aspirators, to make all of the connections properly. 
The rabbit was therefore under the bell jar, in each determination of 
carbonic acid, for exactly thirty-two minutes. The aspirators were 
started simultaneously and their progress carefully watched, in order 
to check any slight irregularity that might show itself. 
The animals experimented with were wholly rabbits, and prelimi- 
nary trials showed us plainly that it was very necessary to have 
them in a condition of hunger during the experiment, in order to 
avoid the irregularities incident to change in digestion. Further, 
we soon found that this was best accomplished by depriving the 
animal of food for three days, after which the experiment was 
commenced and allowed, as a rule, to extend through three con- 
secutive days, the animal being deprived of food during the entire 
period. On the first of the three days, eight determinations of 
carbonic acid were made and the results obtained were used as a 
control, with which to compare the results obtained on the two fol- 
lowing days, when the animal was being dosed with the substance 
experimented with. This, as a rule, we found to be the most satis- 
factory method of procedure, since small differences could not be 
relied upon as expressing anything of importance; for the varying 
restlessness of the confined animal, involving more or less muscular 
activity, would many times lead to variations in the amount of car- 
bonic acid excreted, as may be noticed in the control experiments on 
those days when the animals were not dosed. Hence, the average of 
several consecutive results must necessarily express more correctly 
the average elimination of carbonic acid than any single result. 
Further, we deemed it better to allow the experiments to extend, as 
a rule, over several days and thus study the action of small, repeated 
doses of the various substances rather than to observe the effects of 
a single large dose, where violent action might naturally be expected. 
The following table of results illustrates the way in which our 
experiments have been conducted, and at the same time. shows the 
extent of variation, in the amount of carbonic acid, to be expected 
under normal circumstances from day to day. In this experiment, 
the rabbit had been deprived of food for three days, and the results 
show the amount of carbonic acid in the 37:5 litres of aspirated air 
for four distinct periods, during the fourth and fifth days. As already 
stated, the total amount of baryta solution employed in the three 
absorption tubes was 250 c. ¢., of which 100 c. c. were used in the first 
TRANS. ConN. ACAD., Vou. VII. 52 . MARCH, 1887, 
