H 
Mr. Home's Lecture 
of compasses ; and the limits of this portion were marked by a 
small pin, passed transversely through the substance of the 
nerve. The part included between the two pins was then se- 
parated from the rest of the nerve, in the following manner. 
The person who was to divide the nerve, had a pair of scissars 
in each hand; and, having passed the point of one of the blades 
under the nerve, above the upper pin, and having done the same 
with a blade of the other pair of scissars, below the lower pin, 
the two pair of scissars were shut at the same moment, and 
the nerve at these two parts cut through. 
This portion was again measured, and, instead of being 
twelve inches, was now only eleven and f ; so that the irritation 
produced by dividing it, had made it contract £ of an inch. 
This experiment was repeated upon several horses ; and in 
all of these repetitions there was a contraction produced : this 
varied in the different experiments, and in some of them was 
only fths of an inch. When the nerve was divided very early 
after the animal had been knocked down, it was the greatest ; 
and, in proportion to the delay that took place, so was the di- 
minution in the degree of the contraction. 
In these experiments, the nerve, as well as the surrounding 
parts, was disturbed as little as possible, that the results might 
be the more readily and more accurately ascertained: this, 
however, makes them liable to an objection, which is, that the 
contraction might be produced by the cellular membrane sur- 
rounding the nerve; an objection which certainly can have little 
weight in the peculiar situation of the phrenic nerve, as it lies 
between the pleura and pericardium, where the cellular mem- 
brane can have little influence over it, while the pericardium is 
left entire. . 
