283 
two series of experiments made by Messrs Allen 
and Pepys, the difficulties, in a physiological point of 
view, greatly accumulate upon us. For, if an ab- 
sorption of oxygen really take place in the lungs, 
how does it happen, that, in the first thirteen experi- 
ments, made with several 1000 cubic inches of air, 
and which occupied from ten to twenty-four minutes 
of time, a very small loss in the whole bulk of air, 
and not the smallest in its proportion of oxygen, oc- 
curred ; while, in two other experiments, made with 
only 30O inches of air, and continued only for three 
minutes of time, a great deficiency in the whole bulk 
of air, and a loss of one-third of its oxygen, took 
place. In all these experiments, except the twelfth, 
in which, instead of loss, there was actually an in- 
crease of eleven cubic inches upon the bulk of air 
respired *, the same person appears to have breathed, 
and the air was of similar composition. Consequent- 
ly, the cause of variation in the result is to be sought, 
not in any difference in the animal organs, or in the 
original composition of the air, but, probably, in 
some circumstances of dissimilarity, which accompa- 
nied the progress of the experiment. 
575. Now the bare statement of facts points out a 
great dissimilarity, not only in the chemical results, but 
in the circumstances accompanying the experiments, 
and in the effects which they produced in the system. 
For in the first thirteen experiments, which occupied 
from ten to twenty-four minutes, and in which no loss 
Phil. Trans. 1808, p. 
