Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Todd, Robert Bentley
could not be entertained : the fifth nerve had 
also been fairly divided: thus far, therefore, 
his conjecture was disproved. Pursuing his 
inquiry still further, he found in his next 
experiment that no indication whatever of pain 
was manifested by the animal on irritation of 
the facial on the side on which the fifth nerve 
had been cut ; but in two succeeding experi¬ 
ments he ascertained that while irritation of the 
nerve anterior to the meatus auditorius pro¬ 
duced no other effect but spasms of the nasal 
and labial muscles, when exerted posterior to 
that point it excited manifest evidence of suf¬ 
fering : this latter circumstance he accounts for 
by the communications of the posterior part of 
the facial with other sentient nerves besides the 
fifth, and he has come to the conclusion that the 
former nerve is not endowed with independent 
sensibility, but that it derives the property from 
the fifth and other sentient nerves : this ques¬ 
tion, however, requires further investigation.* 
Relation of the fifth pair of nerves to the 
special senses.—The organs of the special senses 
are in the higher classes and in the case of 
smell, sight, and hearing, each supplied with 
nerves from at least two sources. Besides the 
particular nerves, which are generally consi¬ 
dered to be the source or medium of the spe¬ 
cial sense, they are furnished with branches 
from the fifth pair; and a question must, at the 
outset, be asked in regard to the two nerves 
derived from these different sources, as to 
which is to be considered the proper nerve of 
the peculiar sense enjoyed? In connexion 
with the two separate nervous supplies, it is 
also to be observed that each organ enjoys two 
kinds of sensibility, viz. the special sensibility, 
through which sensations of the particular sense 
are received, and the general sensibility, in 
which the several organs of the body partici¬ 
pate, and which is the medium through which 
impressions of contact are conveyed. The exis¬ 
tence of the special sense, die coincidence of 
the particular nerve, the impairment or loss 
of the special function uniformly consequent 
upon the injury or destruction, whether by 
disease or otherwise, of that nerve ; and the 
community both of function and distribution, 
displayed by the nerve from which the organs 
of the senses are in common supplied, have 
led physiologists generally to the conclusion 
that in each case the particular nerve is the 
medium of the special sense, and that the 
fifth nerve confers upon the organs of the spe¬ 
cial senses general sensibility only. The con¬ 
clusion thus commonly adopted has been at 
different times called in question : thus Mery 
and Brunet, in 1697, denied to the nerves of 
the first pair the function of smell, and attri¬ 
* Eschricht, de functionibus nervorum faciei et 
olfactus organi, Hafn. 1825. [The superficial tem¬ 
poral nerve doubtless contributes mainly to supply 
sensibility to the posterior twigs of the facial : but 
so much difficulty do some see in satisfactorily 
accounting for the sensibility of the portio dura, 
that they find it convenient to discover two roots of 
origin, and a ganglion on one, thus reducing it to 
the class of compound nerves. See Arnold, leones 
capitis nervorum ; also Gaedechens, nervi facialis 
physiologia et pathologia.—Ed.] 
buted this sense to the fifth nerve.* The ques¬ 
tion of the connexion between the fifth nerve 
and the special senses is one of much difficulty, 
and probably we are not as yet in possession of 
sufficient data from which to draw a positive 
conclusion upon it when viewed in all its bear¬ 
ings. It resolves itself into three: 1. how far 
the nerve may be concerned in the perception 
of special sensations in those cases in which 
nerves, considered to be specially intended for 
their perception, exist: 2. how far its co¬ 
operation or influence may be necessary to 
enable the special nerves to fulfil their func¬ 
tions: 3. how far it may be capable of taking 
the place of those special nerves, and of be¬ 
coming, under certain conditions, media of 
perception to sensations, for which, in other 
cases, peculiar nerves are conferred. We shall 
review the relation of the nerve to the several 
senses in succession, bearing in mind the three 
points to which our attention is to be directed. 
That it is a medium of perception in the case 
of two senses, viz. touch and taste, is already 
so universally acknowledged that it is unneces¬ 
sary to dwell upon the point. 
The importance of the fifth nerve in the 
three other senses of smell, sight, and hearing, 
has been advocated by several physiologists, 
and more particularly by Magendie, who ap¬ 
pears disposed to view the fifth nerve as the 
source or medium of all the three. His appli¬ 
cation of this doctrine, however, has reference 
more particularly to the sense of smelling, 
upon which he has performed a series of expe¬ 
riments, of which the following is a summary: 
he destroyed entirely the olfactory nerves within 
the cranium, and he found the animal still 
sensible to strong odours, such as ammonia, 
acetic acid, essential oil of lavender. The sen¬ 
sibility of the interior of the nasal cavity had 
lost nothing of its energy; the introduction of 
a stylet had the same effect as upon a dog 
which had not been touched. This experiment 
he performed several times, and always with 
the same results. He next divided the fifth 
nerves within the cranium, of course before 
they had given branches to the nostrils, 
and found all trace of the action of strong 
odours to disappear. He hence concluded that 
smell, in so far as pungent smells are con¬ 
cerned, is exercised by the branches of the 
fifth pair, and that the first is not concerned in 
the function. To this conclusion he himself 
starts the objection that the agents used are not 
odours, properly speaking, but chemical, pun¬ 
gent, irritating vapours, and that by the section 
of the fifth we destroy not the sense of smell, 
but only the sensibility of the membrane of the 
nose to these irritating vapours, and he admits 
the force of the objection with respect to some 
of the vapours alluded to ; but he denies that 
it will apply to the oil of lavender or that of 
Dippel, the effect of which in the experiments 
is the same. In order to remove the difficulty 
he destroyed the olfactory nerves of a dog of 
particularly fine nose, and then enclosing por¬ 
tions of food of various kinds in paper, he 
* See Journal Complementaire, v. 20. 


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