284 
of oxygen occurred, the air was only once passed 
through the lungs, the breathing was nearly natural, 
the operator scarcely fatigued, and his pulse not 
raised more than about one beat in a minute *. 
But in the two experiments, in which oxygen is said 
to be absorbed, the same air was passed eight or ten 
times through the lungs ; and, in less than a minute, 
the operator found himself obliged to take deeper 
and deeper inspirations. At last, the efforts to take 
in air became very strong and sudden, with a great 
sense of oppression and suffocation in the chest, in- 
distinct vision, buz in the ears, loss of recollection, 
and, at the end of three minutes, perfect insensibi- 
lity |. This difference in the effects produced in 
the system, we do not hesitate to ascribe to a dif- 
ference in the composition of the air (91. 92.), 
which, in the first experiments, was respired in a na- 
tural state, but, in the two last, by repeated breath- 
ing, was rendered more and more unfit to carry on 
respiration, until, at length, its power of supporting 
that function altogether ceased. 
576. But because under circumstances, in which 
the mental and animal powers were in complete 
abeyance, the respiratory organs were not able to 
make so complete an expulsion of the inspired air as 
they effect in their natural state of health and vigour, 
are we, therefore, entitled at once to conclude, that all 
the air which was not expelled was really absorbed? 
Setting aside the anatomical difficulties in the case, let 
us, for a moment, look only to the chemical conse- 
* Phil. Trans. 1808, p. 253. f Ibid. p. 26'0. ?62. 
