172 Mr. Bell on the nervous circle which connects 
is further exemplified in the sensibility of the skin to heat ; 
whilst, on the contrary, a muscle touched with a hot or cold 
sponge during an operation, gives no token of the change of 
temperature but by the degree of pain. 
Many of the nerves which perform the most delicate ope- 
rations in the oeconomy, are not more sensible to pain than 
the common texture of the frame. The lower degree of sen- 
sibility to pain possessed by the muscles, and their insensi- 
bility to heat, is no argument against their having nerves 
which are alive to the most minute changes of action in their 
fibres. 
When the anatomist shall find both the portio dura of the 
seventh and the fifth going to the integuments of the head 
and face, he may naturally ask, why are there two nerves to 
the surface ? and he will probably reflect, that although the 
principal office of the nerves of the skin is to convey impres- 
sion to the sensorium, yet the influence of the mind is con- 
veyed to the surface. The condition of the mind in passion, 
for example, is as forcibly communicated to the skin as to 
the muscles themselves ; and therefore if a branch of the fifth 
be necessary to convey sensation from the surface to the 
sensorium, the seventh is necessary to the change of vascular 
action, and to the condition of the pores when affected by a 
cause proceeding from within, outwards. 
I feel a hesitation when I reason upon any other ground 
than on the facts of anatomy. Experiments are more apt to 
be misinterpreted ; and the very circumstance of a motor and 
