- 720K 
or toes.* Insuch cases the central segments 
of the amputated nerve-fibres remain; if they 
retain their healthy condition, they continue 
to represent in the sensorium the various 
points on the surface of the amputated limb, 
and likewise the muscles which they were 
destined to supply. If, however, the inte- 
gtity of the nerve-fibres has been impaired in 
consequence of any morbid action which may 
have followed the operation, then the sensation 
exists imperfectly or not at all. 
It may be stated in connection with this 
subject, and in confirmation of the view above 
taken, that in many cases of complete paralysis 
of a limb from cerebral disease, the patient, 
although perfectly clear in his general mental 
perceptions, is not conscious of the presence of 
the paralysed member, and really feels as if it 
did not exist. I have known instances in 
which this unconsciousness has been so great 
that the patient has actually mistaken the para- 
lysed part for the limb of some other person 
coming in contact with him, or for some en- 
tirely foreign substance. One man fancied that 
his paralysed arm was bis wife’s, and called to 
her to take itaway. In such cases the morbid 
state of the brain prohibits the developement 
of that affection of the centre of sensation upon 
which the feeling of the connection of the limbs 
depends.t 
The same law of action applies to nerves of 
a as to those of common sensation. 
hus, whilst ordinarily they propagate to the 
centre impressions made at the periphery, we 
find nevertheless that irritation of the nervous 
trunk at any part of its course may give rise 
to its peculiar sensation; and if the brain be 
stimulated at the part in which the nerve is 
implanted, similar sensations may be produced. 
The phenomena of vision and hearing which 
are excited in these ways are called “subjective ;” 
they are familiarly known to medical men as 
not unfrequent precursors of more serious 
symptoms of cerebral disease. Musce voli- 
tantes, ocular spectra, and tinnitus aurium, are 
the most common instances of these pheno- 
mena. Pressure on the eyeball, a galvanic 
current passed through it or very near it, rota- 
tion of ike beady, are capable of giving rise to 
similar phenomena, by exciting the retina or 
the central connections of the optic nerve, or by 
disturbing the circulation of the blood in them. 
A sense of giddiness, similar to that produced 
* Miiller records several instances in his Physio- 
logy, vol. i. p. 746. ( Eng. edition. 
There is a man now in King s College Hospital 
who suffered amputation at the upper third of the 
arm, and whose entire scapula, with the shoulder 
joint and great part of the clavicle, was removed by 
Mr. Fergusson within the last two months, i 
man still feels his fingers, 
t Valentin states that persons who are the sub- 
jects of congenital imperfections, or absence of the 
extremities, have nevertheless the internal sensa- 
tions of such limbs in their ect state. Accord- 
ing to the view above taken this could not be, 
unless the primitive nervous fibres are present 
in their fall number in the trunks of the nerves des- 
tined for the limb. Repertorium far Anat. und Phys. 
1836, p. 330, and note to Baly’s translation of 
Miiller’s Physiol. vol. i. p. 747. 
PHYSIOLOGY OF THE NERVOUS SYSTEM. 
by the means last-named, is also a very com- 
mon symptom of cerebral affection arising from 
a disturbed circulation, or from the blood being 
deficient in one or more of its staminal princi- 
ples, or vitiated by some morbid elemeut. 
The stimuli of nerves—Nervous action is 
ordinarily provoked by stimuli of two kinds, 
mental and physical. Menta) stimuli are those 
resulting from the exercise of the will, or from 
thought. Physical are due to some external 
excitant; light, heat, sound, mechanical stimu-— 
lation, chemical substances, as acids or alkalis, — 
or electricity. 4 
In all voluntary movements an act of the 
mind is the excitant of the nerve. ions 
are caused generally by the influence of physi- 
cal agents upon the peripheral extremities 
nerves, which communicate with the sensorii 
commune. The change thus produced in thi 
nerve gives rise, through the medium of this 
communication, to a corresponding affection 
the mind. A mental stimulus, however, 
affect a nerve of sensation. Such stimulu 
would originate in that part of the brain cl 
is the seat of the changes connected with thi 
intellectual actions, and affecting the centre o 
sensation, would excite in certain 
nerves a change similar to that which a physic 
stimulus applied to their oe eral extremiti 
is capable of producing. In this way the mit 
is capable of exciting pain in any part. W 
the attention has been long directed to a 
particular situation, whether it has been 
viously the seat of ize or not, painful sen 
tions may be excited there. this we 
many instances in practice. In the treatm 
of cases of hysteria it is of great impe 
on this account, to direct the attention of 
pence: as much as possible away from 
ocal affection. 
Motor nerves are never immediately exci 
by a physical stimulus in the ordinary acti 
of the body. A physical stimulus acts w 
motor nerve always through a sensitive ner 
the actions thus produced are, commonly, cal 
reflex actions from the apparent reflexion 6 
change excited by the afferent or sensitive 
in the nervous centre into the motor or ef 
nerve. This class of actions was first po 
out and described by Prochaska, who v 
them as consisting “ in reflexione impress 
sensoriarum in motorias.” The contact 
foreign substance, pressure, titillation, are 
ordinary physical means by which such at 
may be excited. As a good example of 
may be quoted the act of deglutition a 
isthmus faucium. 
Physical stimuli of other kinds, 
may excite motor nerves. The pre 
morbid growth of any kind may irritate 
nerves and create spasm of the musel 
supply. Any virulent fluid applied to: 
nerve will irritate in a similar way—hot 
—liquor potasse—a mineral acid—a sol 
of strychnine, &e. And for the same f 
7a 
: 
certain morbid matters in the blood may 
nerves whether sensitive or motor, causit 
so-called neuralgic pain in the one case, 
cramp or spasm in the other. 
