317 
bronchial cells, and no air is supposed either* to en* 
ter their absorbent vessels, or to penetrate their sub- 
stance. It may not be easy to assign the immediate 
cause of such a phenomenon, but some facts render 
it probable that it may be connected with the elec- 
trical states of the atmosphere, and of the animal 
substance. The air of the atmosphere is known to 
be always more or less charged with electric matter ; 
and in the experiments of Mr Wilson, a few blasts 
of air from a common bellows, especially when the 
pipe of the bellows was previously heated, were 
found sufficient to render the tourmalin, glass, and 
amber positively electrified *. But during respira- 
tion, the air undergoes a change in its electrical 
state ; for Mr Read found, that the air, depraved by 
respiration, always indicated a negative state of elec- 
tricity, while the surrounding atmosphere was in a 
positive state f It is, therefore, conceivable, thatj 
in the act of drawing off its electric matter, a recipro- 
cal attraction may be exerted between the animal 
substance and the air, by which the elasticity of the 
latter may, for a time, be diminished ; and this cause^ 
operating over so great an extent of surface in the 
lungs, may possibly contribute to reduce the whole 
volume of air. 
616. Farther, the opinion that has now been sta- 
ted, presents nothing inconsistent with, or adverse to 
the chemical changes which the air experiences in 
the lungs ; but, on the contrary, the union of the 
* Priestley's Hist Elec. p, 212. 
f Phil. Trans. 1794, p. 267. 
