io Mr. Carlisle's Lecture 
By this simple disposition, the medullary substance of nerve 
is spread through all organized, sensible, or motive parts, 
forming a continuity which is probably the occasion of sym- 
pathy. Peculiar nerves, such as the first and second pairs, and 
the portio mollis of the seventh, terminate in an expanse of 
medullary substance which combines with other parts and 
membranes, still keeping the sensible excess of the peculiar 
medullary matter. 
The peculiar substance of nerves must in time become inef- 
ficient ; and, as it is liable to injuries, the powers of restoration, 
and repair, are extended to that material. The reunion of 
nerves after their division, and the reproduction after part of a 
nerve has been cut away, have been established by decisive 
experiments. Whether there is any new medullary substance 
employed to fill up the break, and, if so, whether the new 
substance be generated at the part, or protruded along the 
nervous theca from the brain, are points undetermined : the 
history of the formation of a foetus, the structure of certain 
monsters, and the organization of simple animals, all seem to 
favour the probability, that the medullary matter of nerves is 
formed at the parts where it is required, and not in the prin- 
cipal seat of the cerebral medulla. 
This doctrine, clearly established, would lead to the belief 
of a very extended commixture of this peculiar matter in all 
the sensible and irritable parts of animals, leaving the nerves 
in their limited distribution, the simple office of conveying im- 
pressions from the two sentient masses with which their 
extremities are connected. The most simple animals in whom 
no visible appearances of brain or nerves are to be found, and 
no fibrous arrangement of muscles, may be considered of this 
