15 
on the Irritability of Nerves. 
As, however, the opinion of the cellular membrane being 
the agent by which the retraction of divided nerves is produced, 
has been very generally received, it was highly proper to attend 
to that circumstance, and have the experiment made in such a 
way as to prevent any other surrounding part from acting upon 
the nerve ; with this view, the following experiment was made. 
Exper. 4. The pleura was removed from twelve inches of the 
phrenic nerve of a horse ; and afterwards the attachments be- 
tween the nerve and pericardium were completely divided: 
under these circumstances, this portion of nerve was separated, 
as in the last experiment. This portion was again measured, 
three hours after, in its detached state, and it was found to 
have lost |ths of an inch in length. The horse was twenty 
years old, and was killed on account of its age, which rendered 
it by no means a favourable subject for such an experiment. 
With a view to determine whether the power of contraction 
in a nerve continued for any length of time after apparent death 
had taken place, and also to ascertain what proportion of elas- 
ticity a nerve possesses, (for every part of an animal body that 
is not rigid, appears to be endowed with it in a greater or less 
degree,) the following experiment was made. 
Exper . 5. Eighteen inches in length of the phrenic nerve 
were measured, and separated by means of scissars : the con- 
traction produced was only of an inch; the experiment being 
made nearly an hour after the horse was knocked down. Upon 
being stretched with force, it elongated to 18 \ inches ; 
and, on being left to itself, retracted to 17 It was kept 
till next day, and again measured, when it was only 1 7 ■§■ : upon 
being stretched, it was elongated to 18 ■§; but, immediately 
on being left to itself, it retracted to eighteen inches. 
