310 
NATURE 
[ Fan. 20, 1870 
related sensory centres from some part of the respiratory 
passages themselves. : ; 
Bearing these facts in mind, and also the psychological 
view of the essential unity in the mode of evolution of all 
sensations or conscious states—whether simple or com- 
plex—we shall find that the performance of many acts of 
the so-called sensori-motor type do not necessarily lend 
such support to the supposition that the sensory ganglia 
are the seats of consciousness as they have been supposed 
to do. That the movements of an infant or of an idiot 
should appear to be automatic in ‘nature, is only to be 
expected if we consider that they are responses to con- 
scious impressions excited in quite undeveloped cerebral 
hemispheres, in which, as yet, the possibilities of intel- 
lectual and volitional action of the lowest type only are 
organised. Thus, the only action which at this time could 
possibly emanate from the operation of the intellectual 
centres would be such as Dr. Carpenter has supposed to 
depend upon the stimulus of mere sensations ; and it does 
not at all follow, as he seems to suppose, that such move- 
ments are excited by sensations, realised as such in the 
sensory ganglia and thence reflected without the inter- 
yenfion of the cerebral hemispheres. Neither do we 
think his doctrine receives any stronger amount of sup- 
port from the fact of our ability to perform certain hadztual 
movements whilst the cerebrum is occupied with some 
engrossing train of thought. 
It is, we think, an altogether improbable assumption 
to suppose that the so-called “secondary automatic ” 
acts take place, as a general rule, altogether without 
the intervention of the cerebral hemispheres. Taking 
the instance cited by Dr. Carpenter, of the individual 
who, falling into a deep reverie whilst making his 
Way through the streets, nevertheless walks with ease 
along accustomed routes, though his attention may be 
entirely absorbed by some particular train of thought, it 
is supposed that these movements are characteristic 
instances of sevsord-motor acts, that they are brought 
about solely by reflections from some of the sensory 
eanglia, and without the intervention of the hemispheres. 
But it seems to us much more reasonable to suppose that 
the cerebral hemispheres have been concerned to some 
extent, even though the consciousness of the individual 
has been otherwise monopolised. In proportion to the 
frequency of the repetition of such movements—to the 
degree in which they have become habitual, so can we the 
more easily understand that the cerebral action involved 
may take place without arousing consciousness, and so 
quite independently of trains of thought which are mono- 
polising the person’s attention. A motor incitation now 
really volitional, may, though similar in all other respects, 
at another time be purely reflex and unconscious, even 
though passing over from regions of the cerebral hemi- 
spheres themselves;* the consciousness or the uncon- 
sciousness of the incitation depending upon the particular 
direction of the attention of the individual at the time 
being. This view seems rendered all the more pro- 
bable if we consider what are the effects on man of 
even small injuries of parts of the cerebral hemispheres 
above the level of the sensory ganglia. If, in the instance 
above alluded to, the person maintains the erect position, 
and even walks perfectly well, through the intervention 
of nerve-centres no higher than the sensory ganglia, how 
is it that the same man would be completely paralysed on 
one side of his body for months or perhaps years by an 
effusion of blood into, or a softening of, a portion. of 
brain tissue quite above these sensory ganglia—by a lesion, 
for instance, of a portion of the opposite hemisphere out- 
side its corpus striatum 2 We may set such an individual 
upon his legs as often as we choose, but no amount of 
mere sensory impressions are capable of exciting the 
supposed sevsori-motor movements ; the paralysed limb 
* See article on ‘‘ Physiology of Thinking,” Jortnightly Review, Jan. 
1869, 
is utterly powerless, and even the mere attitude of stand- 
ing, when the individual is unsupported, is found to be 
impossible. 
The experimental evidence which has been appealed to 
is also capable of receiving different interpretations ; and, 
indeed, physiologists themselves have already expressed 
directly contrary opinions upon this subject. The evidence 
is, in fact, of such an uncertain nature as to be quite in- 
capable of leading to a very definite conclusion, unless we 
have formed some decided opinion as to the real nature of a 
sensation, and as to how this differs from what is called a 
perception. Flourens denies, for instance, that birds or 
mammals whose cerebral hemispheres have been removed 
are any longer capable of appreciating sensory impressions ; 
whilst Magendie, Longet, Vulpian, and many others main- 
tain that such animals are capable of feeling simple sen- 
sations, and that they are therefore, to a certain extent, in 
possession of consciousness. But it may be fairly main- 
tained that the way in which such animals respond to 
external influences acting upon them are explicable with- 
out postulating the existence of consciousness, if we bear 
in mind that they do still retain their sensory ganglia and 
all the related motor centres in organic connection with 
these ; and if we bear in mind also what has been already 
said as to the degree in which impressions, reaching only 
so far as these sensory ganglia, and not revealing them- 
selves in consciousness at all, are, nevertheless, yalified, 
and therefore capable of exciting those purposive move- 
ments which exist potentially in the related motor centres in 
the form of definite nerve connections, The molecular mo- 
bility of these centres has only to be disturbed in order to 
bring about, with machine-like precision, the natural move- 
ments themselves. Longet and Vulpian look upon the poms 
Varolid as the seat of general sensibility,* and there cer- 
tainly seems much more evidence in favour of this view than 
in support of the doctrine of Dr. Carpenter that such is the 
function of the optic thalami. Evidence of different kinds 
seems quite opposed to the latter view ; but much say be 
said—even though, as we think, to little purpose—in 
favour of the opinion of Longet and Vulpian. The co7- 
pora guadrigemina are similarly supposed to be the seats 
of perception for optical impressions, And one of the 
strongest facts that has been recorded in favour of the 
supposed sezsorvz-motor nature of certain movements was 
observed in a pigeon, which lived eighteen days after its 
cerebral hemispheres alone had been removed by Longet. 
When this animal was taken into a dark room, every time 
a light was brought near its eyes the irides contracted, and 
often even winking occurred ; “ mais chose remarquable,” 
Longet says,} “aussit6t que j’imprimais un mouvement 
circulaire 4 la bougie enflammeée, et a une distance assez 
grande pour qu’il n’y eit point sensation de chaleur, le 
pigeon exécutait un mouvement analogue 4 sa téte.” 
Nevertheless, it is said that this same animal sometimes 
seemed to avoid obstacles, and sometimes knocked 
himself against them. So that when we consider how 
closely the movements of the eyes are bound up with 
visual impressions generally, this following of the strong 
light, which seems so much to suggest consciousness, 
may be capable of explanation without having recourse 
to such a supposition. Dr. Carpenter has called attention 
to the fact that when the eyelids are closed, if we attempt 
to move the eye-balls in any given direction, we can only 
do this with considerable difficulty, and with an extreme 
sense of effort—“ This sense being the result of the state 
of tension in which the muscles are placed by the effort to 
move the eyes without the guiding visual sensation.” He 
then adds :—“ Now, on the other hand, the will may 
determine to fix the eyes upon an object ; and yet this 
* These conclusions weré arrived at from an observation of birds and 
mammals whose cerebral hemispheres, corpora striata, thalami, corpora 
quadrigemina, and cerebellum had been all removed, leaving within the 
cranial cavity only the poxs, or txber annulave, and the medulla, (Longet, — 
““Traité de Physiologie,” 3rd ed. t. ili. p. 156.) 
t Loc. cit. p. 428; 
a oe 
