ON THE EXTERNAL CAUSES OF DISEASE. 221 
Lavoisier ascertained that when the air out of doors consisted 
of 
I t 4 
27 parts of oxygen 
and 73 — nitrogen 
100 
the air in the lowest ward in the General Hospital at Paris con- 
tained but 
25 parts of oxygen, 
and 71 — nitrogen, 
and 4 — fixed air, 
,100 - 
• X . x * 4 
And when, before the play, the air in the theatre of the Tulie- 
ries contained the usual proportion, towards the conclusion of 
the piece, which was acted before an unusual concourse of spec¬ 
tators, it contained 
but 21 parts of oxygen, 
and 76£ — nitrogen, 
and 2J — fixed air. 
Whence it is evident that the quantity of oxygen or vital air had 
been diminished in the theatre in the proportion of 27 to 21, or 
nearly one-fourth; that is, it was one-fourth less fit for respira¬ 
tion than before. 
From these examples, the air of an atmosphere which is origi¬ 
nally composed of two fluids, in all ill-ventilated stables con¬ 
tains three aerial fluids. These three serial bodies, though blend¬ 
ed together, arrange themselves in rather a singular manner. 
There is something mysterious in the composition of such an 
atmosphere, which cannot be accounted for any theory that is 
merely chemical, and still less by the doctrine of gravity. Where 
the three gases are combined, so as to form an atmosphere, gra¬ 
vity may keep the three gases as a whole near to the surface of 
the earth ; but neither gravity, chemistry, nor electricity, will en¬ 
able us to explain why the lighter gases lift up those that are 
heavier, and hold them in a state of permanent suspension, even 
in the air of the highest atmosphere that has been examined. 
The air that is expired is a compound of nitrogen and carbonic 
acid: this compound is unfit for respiration or combustion ; it 
soon contaminates the atmosphere in close places, and renders 
it no longer respirable. The carbonic acid gas, which, is the 
heaviest and most poisonous , is no sooner exhaled, than it is im¬ 
mediately lifted up. By what power this is effected, w T e are ig¬ 
norant of: w 7 e may w r ell exclaim with the poet,— 
VOL. vn G g 
