SIR CHARLES BELL ON THE NERVOUS SYSTEM. 
251 
When the dissected body exhibits to us this extensive class of respiratory nerves, 
traceable from a centre to all the organs of respiration, a question arises, by what 
means do the sensibilities of the pharynx, larynx, lungs, stomach, bring these respi- 
ratory nerves and muscles into action ? Is the system which we have been considering 
complete in itself? Are these respiratory nerves both sensitive and muscular ? Are 
the necessary sensations propagated along sensitive nerves bound up with the mus- 
cular respiratory nerves, or do they owe their sensibility to the numerous connexions 
with the regular nerves formed in their course ? 
That a regular nerve may animate the whole class of respiratory nerves is demon- 
strated in the office of the fifth, in the Schneiderian membrane. The sensibility of 
the cavities of the nose bestowed by the branches of the fifth nerve, excites the act of 
sneezing. 
But, on the other hand, if we place confidence in the experiments of Valentin on 
the roots of the Vagus , it is purely the central sensitive nerve of the respiratory sy- 
stem ; for having exposed its roots, and taken them off from the side of the medulla 
oblongata, and at the same time having separated them from the roots of the glosso- 
pharyngeal nerve and spinal accessory nerve, he irritates these roots of the vagus, 
and finds no consequent action in the pharynx, stomach, or respiratory muscles : no 
motion is produced. 
But again, taking the trunk of this nerve, where it lies in the neck, all the con- 
nexions of the nerve being entire, the irritation of it produces muscular actions, and 
the act of respiration is imitated. 
There is no doubt that the nervus vagus is a sensitive nerve. When I have examined 
the abdomen of a man completely paralytic from disease, or from fracture of the ver- 
tebrae high up, the patient, though outwardly insensible below the neck, has felt when 
I pressed the stomach. 
Again, with respect to the glosso-pharyngeal nerve, the experiments of Dr. Reid 
go to prove it a sensitive nerve. It is impossible to cavil at these experiments. They 
were often repeated, and with a perfect understanding of the subject. He first finds 
that pinching the nerve gives pain. He then divides the nerve, and irritates the 
divided portion next the brain, by which muscular movements are produced in the 
throat. 
I am well aware that, dissecting deep among nerves, the experimenter is subject to 
be mistaken ; and in surgical operations on the human body, the exposed trunks of 
nerves give little pain, compared with the fine sensibility of their extremities. We 
find experiments by different hands giving different results, and the same experiments 
differing on one day from another, performed by the same person. 
But the force of evidence is all in favour of the nervus vagus and the glosso-pha- 
ryngeal nerve being sensitive. And Dr. Reid’s experiments give a perfect example 
of what I have called the Nervous Circle* ; the sensibility or nervous influence flow- 
* Phil. Trans. 1826. p. 163. 
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