PHYSIOLOGY OF THE NERVOUS SYSTEM. 
corresponding sensorial impression; and from 
the connections which subsist between the reti- 
ne, and still more from that between the cen- 
tres of sensation, these impressions become 
fused into one. In like manner the organie 
changes in the two brains developing nervous 
force in similar modes and proportions, each 
being capable of affecting the mind similarly, 
although perhaps not identically, are yet so 
united in their action that the double organic 
affection acts on the mind as one. But if, 
through default of the connecting media of the 
two brains, or through lesion of one, the organic 
changes in each do not harmonise with those 
in its fellow, then it is plain that two separate 
and distinct mental affections will result, and 
more or less of confusion must ensue. I can 
see no ground for inferring the existence of two 
minds from such a supposition. The confu- 
sion results from the want of simultaneous 
affection of the same mind by two distinct and 
Separate brains. If, in vision, each centre of 
Sensation affected only its own mind, or, in 
other words, de d only its own mental 
_ phenomena, as Dr. Wigan’s theory would 
_ Compel us to assume, then each mind would 
pereeive a different pective projection 
of the object presented to the eyes, and an 
elaborate and eomplex mental process would 
be required to combine the two sensorial im- 
pressions. How much simpler is the view of 
ony cess which assigns the combination of 
the brain of each physical change in the retina ; 
8o that, in truth, but one impression, different 
each of its excitant ones, reaches the 
mind. So also, in the normal intellectual ac- 
tion, the organic changes of the two brains are 
united by the various transverse commissures, 
so that but one physical stimulus affects the 
mind and excites but one train of thought. 
Not so, however, when from any defect in the 
brains themselves, or in the commissures, the 
Le bana conditions necessary for the organic 
es of the two brains cannot be fulfilled. 
Dr. Wigan’s theory is inconsistent with the 
acknowledged fact of the existence of an im- 
ae symmetry of the convolutions in per- 
§ possessing the highest order of mind. If 
the two brains always act in harmony, there 
ought to be perfect symmetry. But if we ad- 
‘mit that the mind may have the initiative, then 
it is easy to understand how one brain may be 
used more than another. 
' That a power exists of using one brain more 
than another, seems probable from the more 
uent and more perfect use of one hand ; 
and the existence of such a power implies also 
te ae of keeping one brain in suspense 
ile the other is acting, under particular cir- 
| €umstances, just as we can suspend the use of 
‘one arm or one finger or one eye, although the 
exercise of its fellow prompts greatly to its 
simultaneous action. 
| Sleep is an affection of the centre of intel- 
Tectual action, a condition rendered necessary 
by the incessant working of the mind. It is 
indicated by the cessation of all mental nervous 
actions. In deep sleep the body is given up 
ble impression to a physical union in- 
723B 
to the physical nervous actions only, without 
which the functions of breathing, circulation, 
&c., could not be carried on. Dreaming occurs 
only in imperfect sleep,—often, if not always, 
just before waking,—and serves to show how 
the organic changes of the centre of intellectual 
action, when uncontrolled, may produce the 
most rapid trains of thought, recalling events 
or impressions that have passed away, and 
which we may have thought had been forgotten. 
Coma is none of the profoundest kind, a 
paralysis, indeed, of the centre of intellectual 
action, as well as of sensation and volition. 
It occurs under states of disease, which induce 
compression of the brain, or under states of 
shock, which suspend or greatly diminish its 
natural changes, as in concussion. Or it may 
be induced by the influence of certain poisons 
of the sedative or narcotic kind, as opium and — 
belladonna, which, if given in too large a dose, 
paralyse first the centres of mental nervous ac- 
tions, and ultimately those of physical nervous 
actions. 
Somnambulism must be regarded as a state of 
intense dreaming, in which the person is 
es pags to the performance of certain acts. 
alking in one’s sleep, the curious changes of 
position which are made under the influence of 
nightmare, and even the most complex actions, 
as walking, or taking things from one place to 
another, or holding a long conversation, are all 
induced by the same state, a morbid condition 
of the centre of intellectual action, generally 
produced by deranged assimilation or great pre- 
vious disturbance of mind. The somnambulist, 
in short, is one who dreams and acts in his 
dream as if he were awake, and as if all the 
phenomena of which he takes cognizance were 
real. 
Delirium is a condition very analogous to 
dreaming. The organic changes in the centre 
of intellectual action are too rapid to be con- 
trolled by the will, or the influence of the 
centre of volition is impaired. The ravings of 
a delirious patient generally take place uncon- 
sciously, as if the centre of sensation were im- 
paired likewise. In most instances, however, 
the patient may be roused; a strong stimulus, 
as in addressmg him with a loud voice, will 
affect his centre of sensation, and he either 
controls his thoughts for a brief space, and 
directs his attention to what is going on, or the 
effect of the stimulus is to direct his ravings 
into some new channel. The incoherent and 
unconnected manner in which thought follows 
thought in the delirious state is sufficient proof 
that the centre of intellectual action requires 
the controlling power of a will for perfect 
trains of thought, as much as any particular 
set of muscles requires the same influence for 
the accomplishment of definite action. 
Delirium, indeed, may be viewed as a sub- 
jective phenomenon of the centre of intellectual 
action, just as ¢innitus awrium or ocular spectra 
are subjective phenomena of the centre of sen- 
sation. 
In analysing the fibres of the centrum ovale 
we find that a large number of them is com- 
missural, but that the greates proportion of 
