of the chest in breathing, speaking, and expression. 309 
there a long drawn sigh, why are the neck and throat con- 
vulsed, and whence the quivering and swelling of the lip, 
why the deadly paleness, and the surface earthy cold ; or 
why does convulsion spread over the frame like a paroxysm 
of suffocation ? 
To those I address, it is unnecessary to go farther, than to 
indicate that the nerves treated of in these papers, are the 
instruments of expression, from the smile upon the infant's 
cheek to the last agony of life. It is when the strong man is 
subdued by this mysterious influence of soul on body, and 
when the passions may be truly said to tear the breast, that 
we have the most afflicting picture of human frailty, and the 
most unequivocal proof, that it is the order of functions which 
we have been considering that is then affected. In the first 
struggles of the infant to draw breath, in the man recovering 
from a state of suffocation, and in the agony of passion, when 
the breast labours from the influence at the heart, the same 
system of parts is affected, the same nerves, the same mus- 
cles, and the symptoms or characters have a strict resem- 
blance. 
Having examined the system of nerves and muscles, which 
are the agents in respiration, in their fullest extent and in all 
their bearings ; having looked at them, in their highest state 
of complication in the human body, and having traced them 
upwards, from the animals of simple structure, and then by 
experiment, and in a manner analytically as well as syn- 
thetically, their relations become obvious. Instead of one 
respiratory nerve, the par vagum, the nerve so called, is found 
to be the central one of a system of nerves of great extent. 
