HAND AND BRAIN
There remains to be considered the source suggested by Professor
Gratiolet, when he turned from the organs in immediate contact with
the arm and hand to the cerebral centre of nerve force. The statements
advanced by him that the anterior convolutions of the left side of
the brain are earlier developed than those of the right, when taken
in connection with the well-known decussation of the nerve-roots,
would account for the earlier development of the muscles and nerves
of the right arm; but his opinion has been controverted by competent
observers. This, however, does not dispose of the question. The
localisation of the mental operations of speaking, naming, and writing
in certain specific cerebral centres, and the recognised functional
relations of those word-centres with other active cerebration, have
given a new significance to the vital action of the brain as the
seat of nerve-force. It was only in 1861 that M. Broca definitely
assigned the posterior part of the third frontal convolution of the
left hemisphere as the seat of articulate speech. More recently this
has been followed up by observations suggestive of some possible
correlation between the reflex action of the cerebral hemispheres on
the limbs; but it has thus far been no more than a passing allusion,
tending to beget observation of possible coincidences, such as
may be found between left-handedness and either an accompanying
transposition of the seat of articulate speech to the right hemisphere,
or some prevailing characteristic of the degree of word-memory in
the left-handed. A recent observer, Dr. J. Batty Tuke, definitely
affirms that “the large proportion of cases of ataxic aphasia occur in
association with right-sided hemiplegia, although others are on record
in which it has appeared in connection with left-sided hemiplegia in
left-handed persons” (_Encyc. Britann._, art. “Aphasia”). In those an
intimate relation is thus established between right or left-handedness
and the development of the opposite cerebral hemisphere.
The special limitation of the researches of Dr. Guiseppe of Pisa to
“the writing of left-handed persons” naturally directed his attention
to this element of cerebration. “Clinical observation and pathological
anatomy,” he remarks, “have clearly shown that in the foot of the
second frontal convolution of the left cerebral hemisphere there is
located a centre for the co-ordination and the memory of the movements
of writing. The destruction of this centre produces _agraphia_, that
is to say, inability to co-ordinate and remember the movements for
writing. This graphic centre is situated on the left hemisphere in
right-handed persons.” At the same time he is careful to assert that
both in this writing-centre, and in that of the foot of the third
frontal convolution, to which is assigned the co-ordination and
memory of the movements for articulate speech: in the case of lesions
impairing their powers, it has been found possible to stimulate the
corresponding centres of the opposite hemisphere so as in more or less
degree to perform their functions; just as the dormant left hand may be
educated to take the place of the paralysed or amputated right hand.
Dr. Guiseppe thus proceeds: “In left-handed persons the centres of the
neuro-psychic factors of language are situate in the right hemisphere,
as has been shown by well-studied cases. These persons, however, learn
to write with the right hand and not with the left. And yet in their
right hemisphere there is a potentiality which is very favourable for
their education in the co-ordination and the memory of the movements
for writing. Left-handed persons perceive that they could learn to
write with greater facility with the left hand than with the right; but
education succeeds in awaking and conveniently bringing into action in
the left-hand sphere a latent cortical centre, which did not present
so favourable a potentiality as that of the right hemisphere. The
possibility of investigating what influence in left-handed persons
practice with the right hand might develop in the left hemisphere for
the explication of language, would certainly constitute a theme for
important study” (_Archivio Italiano_, September 1890, pp. 306, 307).
With the attention that is now definitely given to this assignment
of the preferential use of one or the other hand to greater or
less development of the opposite cerebral hemisphere, renewed
observation has been directed to the cerebral source of predominant
right-handedness. The discussions in the columns of _Science_,
suggested by Professor Baldwin’s study of its first manifestations,
have revived the reference of it to the assumed excess in development
of the left cerebral hemisphere. Dr. T. O’Connor of New York thus
reasserts it as an unquestionable though little-known fact: “But it
may not be generally known that the left cerebral hemisphere is larger
than the right, its inner face (at the great longitudinal fissure)
coming very near to the middle line, while the corresponding inner edge
of the right hemisphere is well to the right of the median line. The
existence, then, of greater nutrition and greater functionating ability
in the left hemisphere might well be assumed. But that there is a
reason for the greater size, development, etc., of the left hemisphere
is evidenced by a study of the conditions of blood-supply to the two
hemispheres. The left carotid artery ascends almost perpendicularly,
so as to form, as it were, an elongation of the ascending aorta, while
the right carotid is given off from the _arteria innominata_. The
right vertebral artery is given off by the subclavian after the latter
has described its arch and become horizontal, but the left vertebral
arises from the apex of the subclavian’s curve. There is thus the
distinct advantage to the left hemisphere of a better blood-supply
because of the much straighter course taken by the great channels
carrying it” (_Science_, 12th December 1890).
This idea of a greater development of the left cerebral hemisphere
has been the subject of considerable diversity of opinion. A marked
difference in the weight of the two hemispheres has indeed been
repeatedly asserted by well-qualified observers as the result of
careful investigation. M. Broca stated that in forty brains he found
the left frontal lobe heavier than the right; and Dr. Boyd, when
describing the results obtained by him from observations on upwards
of 500 brains of patients in the St. Marylebone Hospital, says: “It
is a singular fact, confirmed by the examination of nearly 200 cases
at St. Marylebone, in which the hemispheres were weighed separately,
that almost invariably the weight of the left exceeded that of the
right by at least the eighth of an ounce.” Dr. Brown-Sequard also,
as hereafter noted, makes this apparent excess in weight of the left
hemisphere of the brain the basis of very comprehensive deductions.
Again Dr. Bastian affirms, as a result of careful observation, that
the specific gravity of the gray matter from the fronted, parietal,
and occipital convolutions respectively is often slightly higher on
the left than it is on the right hemisphere. The opinion is thus
sustained by some of the most eminent physiologists who have given
special attention to the brain and its functions. But, on the other
hand, Professor Wagner and Dr. Thurnam both state that their careful
independent investigations failed to confirm the results arrived at
by M. Broca and Dr. Boyd. From the weighing of the two hemispheres of
eighteen distinct brains, Professor Wagner found the right hemisphere
the heavier in ten, and the left in six cases, while in the remaining
two they were of equal weight. Dr. Thurnam, without entering into
details, states that the results of his weighings did not confirm
Dr. Boyd’s observations; adding that “fresh careful observations are
certainly needed before we can admit the general preponderance of the
left hemisphere over the right.” Though the two hemispheres of the
brain are sufficiently distinct, they are united at the base; and even
with the most careful experimenters, the section through the cerebral
peduncles and the corpus callosum is so delicate an operation that a
very slight bias of the operator’s hand may affect the results. That
a difference, however, is occasionally demonstrable in the weight of
the two hemispheres is unquestionable, and the whole tendency of the
most recent investigation is to sustain the hypothesis which refers the
cause of left-handedness to an exceptional excess of nervous force in
the right cerebral hemisphere. But the results to be anticipated from
the partial character of the bias in the majority of the right-handed
would tend to suggest a doubt as to the full acceptance of the
statement of Dr. O’Connor adduced above. It is rather in accordance
with what has already been affirmed as to the very partial prevalence
of any strongly defined bias in the majority for the preferential
use of either hand, that many brains should come under the notice of
careful observers where little or no difference can be found between
the two hemispheres. But weight is not the only element of variation.
Dr. Bastian, in _The Brain as an Organ of Mind_, draws attention to the
unsymmetrical development of the two hemispheres as one of the most
notable peculiarities of the human cerebrum. This is not only the case
with reference to the number and arrangement of the convolutions, but
it has been noted by various anatomists that the left hemisphere is
very frequently slightly longer than its fellow.
But interesting light has been thrown by pathological observations on
the comparative relations of the cerebral hemispheres; and in this
more than in any other direction we may look for further elucidation.
As already noted, Sir Charles Bell affirms a general inferiority in
muscular strength and in vital properties of the left side of the body,
and a greater liability to disease in the left extremities than the
right. On the other hand, Dr. O’Connor refers a greater susceptibility
to disease of the left hemisphere of the brain to what he assumes
as the source of superior vital force. Having assigned the causes
of greater development as already cited, he proceeds to affirm that
“the greater directness of communication between the heart and left
hemisphere explains the greater readiness with which the latter is
subjected to certain forms of disease. A clot of fibrine whipped off
a diseased valve is carried much more readily because of the direct
route (_viâ_ the carotid) to the left hemisphere; and in conditions
of degenerative weakness of the arteries in general, those of the
left hemisphere being subjected to greater pressure in their distal
ramifications, will be more apt to yield than corresponding ones in
the right.”
Dr. Bastian, when commenting in his _Brain as an Organ of Mind_ on
the specific location of the cerebral function of articulate speech
in the third left convolution of the brain, remarks: “It has been
thought that a certain more forward condition of development of the
left hemisphere--as a result of hereditary right-handedness recurring
through generation after generation,--might gradually become sufficient
to cause the left hemisphere to take the lead in the production of
speech-movements. Some little evidence exists, though at present it
is very small, to show that it is left-handed people more especially
who may become aphasic by a lesion of the right third frontal gyrus.”
Dr. Bastian further assumes it to be indisputable that the greater
preponderance of right-hand movements in ordinary individuals must tend
to produce a more complex organisation of the left than of the right
hemisphere; and this both in its sensory and motor regions. With the
left-handed, however, so many motives are constantly at work tending to
call the right hand into play, that the compensating influences must
in their case tend to check any inequality in the development of the
two hemispheres; so that there would seem rather to be a probability
in favour of a more equable, and consequently healthful development of
both cerebral hemispheres in the left-handed, but really ambidextrous
manipulator. But it is to be noted that while Dr. Bastian recognises a
correlation between the development of one or other cerebral hemisphere
and the greater dexterity of the opposite hand, he is inclined to
recognise right or left-handedness as the cause rather than the effect.
Dr. Brown-Sequard, who strongly favours the idea of superiority, both
in size and weight, of the left over the right cerebral hemisphere,
also ascribes the source of this to the greater frequency and energy
of all right-hand movements. He reverts to an argument derived from
left-handedness when discussing his theory that the two hemispheres
practically constitute two distinct brains, each sufficient in itself
for the full performance of nearly all mental operations; though each
has also its own special functions, among which is the control over the
movements and the organs of opposite sides of the body. “Every organ,”
he says, “which is put in use for a certain function gets developed,
and more apt or ready to perform that function. Indeed, the brain
shows this in point of mere size; for the left side of the brain, which
is used most, is larger than the right side. The left side of the brain
also receives a great deal more blood than the right side, because its
action preponderates; and every organ that acts much receives more
blood.” He accordingly affirms that the growth of the brain up to forty
years of age, if not indeed to a considerably later period of life, is
sufficiently marked to require the continued enlargement of the hat.
The evidence he adduces, based on observing that a hat laid aside for
a time and then resumed, always proved to be too small, is probably
deceptive. But the growth of the adult brain is no longer disputed.
It was indeed affirmed by earlier physiologists, as by Sœmmering,
the Wenzels, and Tiedemann, that the brain attained its greatest
development not later than seven or eight years of age. But this idea
is now entirely abandoned; and--without going so far as to affirm with
Dr. Brown-Sequard, who claims that at the age of fifty-seven he found
by the test of hat measurement that his head had enlarged within every
six months,--the latest observers adduce proof of continuous increase
of brain weight, if not of bulk, until the greatest average weight is
reached between thirty and forty years of age.
On the assumption of Dr. Brown-Sequard that the left hemisphere of
the brain exceeds that of the right both in size and weight: in the
deviations from this normal condition there ought to be found the
corresponding development of the organ brought into use. But, like
most other right-handed reviewers of the phenomena of left-handedness,
he fails to appreciate the bearings of his own argument in the case
of a left-handed person conforming in many ways to the usage of the
majority, yet instinctively giving the preference to the left hand.
He dwells on the fact that very few left-handed persons have learned
to write with the left hand, and that those who can do not write
nearly so well with it as with the right hand. Even in persons who
are left-handed naturally, so that the right side of the brain may be
assumed to control the reasoning faculties and their expression, he
argues that the left side of the brain “can be so educated that the
right hand, which that side of the brain controls, produces a better
handwriting than that by the left hand, though that is controlled
by the better developed brain.” But the reasoning is alike partial
and misleading. The left-handed person systematically submits to
disabilities in his efforts to comply with the usage of the majority,
not only in holding his pen in the right hand, but in the direction and
slope of the writing. A left-handed race would naturally write from
right to left, sloping the letters towards the left, and so would place
the right-handed penman at a like disadvantage, wholly independent
of any supposed change in the functions or preponderating energy of
either hemisphere of the brain. But even in the absence of practice,
the command of the left hand in the case of a truly left-handed person
is so great that very slight effort is required to enable him to write
with ease with that hand.
Reverting once more to the singularly interesting phenomena whereby
in certain conditions of cerebral disease, or local injury, the
correlation between articulate speech, writing, and even the
unconscious expressiveness of gestures, used certain specific
convolutions of the left hemisphere, Dr. Pye-Smith says: “The opinion
that some difference between the two sides of the brain has to do
with our preference for the right hand over the left may, perhaps,
be supported by two very interesting cases of aphasia occurring in
left-handed persons, recorded by Dr. Hughlings Jackson and Dr. John
Ogle. In both these patients there was paralysis of the _left_ side;
so that it seems likely that in these two left-handed people the right
half of the brain had the functions, if not the structure, which
ordinarily belong to the left. To these cases may be added a very
remarkable one published by Dr. Wadham (_St. George’s Hospital Report_,
1869). An ambidextrous or partially left-handed lad was attacked with
left hemiplegia and loss of speech; he had partly recovered at the
time of his death, twelve months later, and then the right insula and
adjacent parts were found softened.”
The remarkable difference in the convolutions of different brains,
and the consequent extent of superficies of some brains over others
apparently of the same size, have been matter of special observation,
with results lending confirmation to the idea that great development
of the convolutions of the brain is the concomitant of a corresponding
manifestation of intellectual activity. But the complexity in the
arrangement of these convolutions, and the consequent extent of
superficies, often differ considerably in the two hemispheres of
the same brain. The variations in shape and arrangement of the
convolutions in either hemisphere may be no more than the accidental
folds of the cerebral mass, in its later development in the chamber
of the skull; and within ordinary limits they probably exercise no
appreciable influence on physical or mental activity.
In so far as right-handedness is a result of organic structure, and
not a mere acquired habit, some trace of it should be found in the
lower animals, though in a less degree. Dr. Buchanan, in discussing his
_Mechanical Theory_, notes that, “while the viscera of the quadruped
have the same general lateralised position as in man, there is a reason
why this should be carried to a greater extent in man than in the
quadruped, owing to the much greater lateral development of the chest
and abdomen of the human figure, in order to adapt it to the erect
posture, as contrasted with the great lateral flattening of the trunk
in quadrupeds. The equipoise is therefore more disturbed in man than in
the quadruped.” In the case of the monkey, its necessities as a climber
no doubt tend to bring all its limbs into constant use; but, possibly,
careful study of the habits and gestures of monkeys may disclose, along
with their ambidextrous skill, some traces of a preference for the
limbs on the one side. The elephant has been repeatedly affirmed to
betray a strongly marked right-sidedness; and this is reiterated in a
communication by Mr. James Shaw to the Anthropological section of the
British Association, where he notes the “curious fact that elephants
have been frequently known to use the right tusk more than the left
in digging up roots, and in doing other things.” But the statement
is vague, and, even if confirmed by adequate proof, can scarcely be
regarded as the equivalent of right-handedness. In dogs it may be
noticed that they rarely move in the direct line of their own body, but
incline to one side or the other, the right hind-foot stepping into
the print of the left fore-foot, or _vice versâ_. In the horse, as in
other quadrupeds, a regular alternation in the pace is manifest, except
when modified by education for the requirements of man. I experienced
no difficulty in teaching a favourite dog to give the right paw; and no
child could more strongly manifest a sense of shame than he did when
reproved for the gaucherie of offering the wrong one. The saddle horse
is trained to prefer the right foot to lead with in the canter; while
the same animal is educated differently when destined for a lady’s
use; but I have been informed by two experienced veterinary surgeons
that, while some horses learn with very slight training to start with
the right foot, others require long and persevering insistency before
they acquire the habit. A curious relation between man and the lower
animals in the manifestation of the organic influences here noted is
indicated by a writer in the _Cornhill Magazine_, when, referring to
the well-ascertained fact that aphasia is ordinarily accompanied with
disease of the right side of the brain, he says: “Right-sidedness
extends to the lower races. Birds, and especially parrots, show
right-sidedness. Dr. W. Ogle has found that few parrots perch on the
left leg. Now parrots have that part at least of the faculty of speech
which depends on the memory of successive sounds, and of the method
of reproducing such imitation of them as a parrot’s powers permit;
and it is remarkable that their left brain receives more blood and is
better developed than the right brain.” The same writer expresses his
doubt as to monkeys showing any tendency to right-handedness; but with
the constant use and training of the hands by the Quadrumana in their
arboreal life, opportunities for the manifestation of any instinctive
preference for either hand must be rare; and is likely to elude all
but the most watchful observers.
A paper was communicated by Dr. Delaunay to the Anthropological Society
of France, on the subject of right-handedness. I only know of it by an
imperfect notice, in which he is reported to look on the preferential
use of the right hand as a differentiation arising from natural
selection, while he regards ambidexterity as a mere “survival.” But Dr.
Pye-Smith long ago remarked that “it is clear that in the progress of
civilisation one or other hand would come to be selected for the more
characteristic human actions for which only one is necessary, such as
wielding a pen or other weapon;” but he recognises the insufficiency
of the suggestion, and adds in a footnote: “The difficult point is to
guess by what process the right rather than the left hand has been so
universally preferred.” He then glances at possible guidance to be
derived from the study of the habits of savage tribes, though still
the old difficulty recurs; and he thus proceeds: “In default of any
better suggestion, might one suggest an hypothesis of the origin of
right-handedness from modes of fighting, more by way of illustration
than as at all adequate in itself? If a hundred of our ambidextrous
ancestors made the step in civilisation of inventing a shield, we may
suppose that half would carry it on the right arm and fight with the
left, the other half on the left and fight with the right. The latter
would certainly, in the long run, escape mortal wounds better than
the former, and thus a race of men who fought with the right hand
would gradually be developed by a process of natural selection.” The
recognition of the shield-hand, and the passive functions assigned
to it, has already been referred to as one familiar to the ancient
Greek and Roman, and no doubt to other and earlier nations. But
here it is diverted to the service of one of the latest aspects of
evolutionary development, and becomes the begetter instead of the
product of left-handedness. To this idea of right-handedness as one
of the results of a survival of the fittest, Dr. Delaunay adds the
statement, professedly based on facts which he has accumulated, that
ambidexterity is common among idiots. The results noted probably
amount to no more than the negative condition of general imbecility,
in which the so-called ambidexterity of the idiot involves, not an
exceptional skill in the left hand, equalising it with the right, but
only a succession of feeble and often aimless actions manifesting
an equal lack of dexterity in either hand. Where left-handedness is
strongly developed, it is, on the contrary, not only accompanied with
more than average dexterity in the organ thus specialised, but also
with a command of the use of the right hand, acquired by education,
which gives the individual an advantage over the great majority of
right-handed men. The surprise occasionally manifested at any display
of dexterity by left-handed performers, as though it were accomplished
under unusual disadvantages, is altogether unjustified. In reality,
a strongly developed left-handedness is, equally with a strongly
developed right-handedness, an indication of exceptional dexterity.
Such skill as that of the left-handed slingers of the tribe of Benjamin
is in no way exceptional. All truly left-handed, as well as all truly
right-handed persons, are more likely to be _dexterous_ than those who
are unconscious of any strong impulse to the use of either hand. The
bias, whether to the right or the left, is, I feel assured, the result
of special organic aptitude. With the majority no well-defined bias
betrays any unwonted power, and they merely follow in this, as in so
much else, the practice of the predominant number. But there is no such
difference between the two hands as to justify the extent to which,
with the great majority, one is allowed to become a passive and nearly
useless member. The left hand ought to be educated from the first no
less than the right, instead of leaving its training to be effected,
imperfectly and with great effort, in later life, to meet some felt
necessity.
Dr. Brown-Sequard, in one of his latest discussions of the closely
related, though much more comprehensive question, “Have we two brains?”
remarks: “We have a great many motor elements in our brain and our
spinal cord which we absolutely neglect to educate. Such is the case
with the elements which serve for the movements of the left hand.
Perhaps fathers and mothers will be more ready to develop the natural
powers of the left hand of a child, giving it thereby two powerful
hands, if they believe, as I do, that the condition of the brain and
spinal cord would improve if all their motor and sensitive elements
were fully exercised.” Without entering on the discussion of the larger
question of the specific duality of the brain, experience shows that
wherever the early and persistent cultivation of the full use of both
hands has been carried out, the result is greater efficiency, without
any counterbalancing defect. Under no enforcement of a violation
of his innate impulses does the left-handed person ever exchange
hands. He acquires an educated right hand and retains the dexterity
of the left. In those cases where, by reason of injury or disease,
the sufferer is compelled to resort to the neglected hand even late
in life, it proves quite possible to train it to sufficient aptitude
for all ordinary requirements. It is therefore obviously the duty of
parents and teachers to encourage the habitual use of both hands; and
in the case of manifest left-handedness, to content themselves with
developing the free use of the right hand without suppressing the
innate dexterity of the left. My own experience, as one originally
left-handed, is that, in spite of very persistent efforts on the part
of teachers to suppress all use of the left hand, I am now thoroughly
ambidextrous, though still with the left as the more dexterous hand.
I use the pen in the right hand but the pencil in the left; so that,
were either hand disabled, the other would be at once available for
all needful operations. Yet at the same time the experience of a long
life assures me that scarcely any amount of training will suffice to
invest the naturally sinister hand, whether it be the right or the
left, with the dexterity due to innate, congenital, and therefore
ineradicable causes. Nevertheless we are bimanous in the best sense,
and are meant to have the free unrestrained use of both hands. In
certain arts and professions both hands are necessarily called into
play. The skilful surgeon finds an enormous advantage in being able
to transfer his instrument from one hand to the other. The dentist
has to multiply instruments to make up for the lack of such acquired
power. The fencer who can transfer his weapon to the left hand, places
his adversary at a disadvantage. The lumberer finds it indispensable
in the operations of his woodcraft to learn to chop timber right and
left-handed; and the carpenter may be frequently seen using the saw
and hammer in either hand, and thereby not only resting his arm, but
greatly facilitating his work. In all the fine arts the mastery of
both hands is advantageous. The sculptor, the carver, the draftsman,
the engraver, and cameo-cutter, each has recourse at times to the left
hand for special manipulative dexterity; the pianist depends little
less on the left hand than the right; and as for the organist, with the
numerous pedals and stops of the modern grand organ, a quadrumanous
musician would still find reason to envy the ampler scope which a
Briareus could command. On the other hand, it is no less true that,
while the experience of every thoroughly left-handed person shows the
possibility of training both hands to a capacity for responding to the
mind with promptness and skill: at the same time it is apparent that in
cases of true left-handedness there is an organic specialisation which
no enforced habit can wholly supersede.
Having determinately arrived at the conclusion that the source
of right-handedness, and so of the exceptional occurrence of
left-handedness, is to be sought for in the preponderant development
of one or other hemisphere of the brain, and that, therefore, the
test has to be sought in the examination of the brains of persons
of exceptional dexterity, whether in the use of their right or left
hand, the difficulty has been to obtain the desired objects of study.
A considerable number of observations are desirable; and those can
only be gradually accumulated as opportunities present themselves
to observant students. As already noted, men of the first eminence
have differed on the question of the greater weight of the left than
of the right cerebral hemisphere; nor does a study of the ordinary
manifestations of right-handedness encourage us to expect a very
marked difference in the cerebral hemispheres in the majority of men.
It need not therefore surprise us to find so able and experienced
an observer as Dr. Thurnam reviewing the data published by Boyd,
Brown-Sequard, and Broca, and expressing as his final conviction
that further careful observations are needed before the general
preponderance of the left hemisphere over the right can be accepted as
an established truth.
As already noted, Dr. Boyd gives as the result of his observations on
upwards of 500 human brains, that the weight of the left hemisphere
almost invariably proved to be in excess of that of the right. In forty
cases Dr. Broca found similar results, and observers of less note
confirm them; so that but for the eminent authorities by whom those
conclusions have been challenged, it would seem presumptuous to refuse
them acceptance. But, countenanced by this conflict of opinion, it may
be permissible to review the question in the narrower aspect of the
present inquiry. Testing it then by a reverse process, and assuming
hypothetically that the exceptionally dexterous right-handed man
will be found to have the left hemisphere the heavier, and the true
left-handed man _vice versâ_, the results arrived at by Dr. Boyd are
altogether in excess of what might be anticipated. The number of the
exceptionally dexterous right-handed, with an invincible instinctive
preference for the use of that hand, though large in comparison with
the no less dexterous left-handed, are nevertheless a minority. Habit,
social usage, and education in all its forms, in the school, the
drawing-room, the workshop, in all the arts of peace, and in nearly
every operation of war, have so persistently fostered the development
of the favourite hand that it is scarcely possible to arrive at any
reliable statistics in proof of the initial proclivities of the large
majority of conformists. Only a prolonged series of observations such
as those already noted by Professor Baldwin, made at the first stage
of life, and based on the voluntary and the unprompted actions of the
child, can supply the needful data. But the careful observations of
many years, prompted by a desire to master the source of an exceptional
instinctive habit, have convinced me that the bias towards the
preferential use of either hand in many, probably in the majority of
cases, is slight. It is sufficient to lead to their following the
practice of the determinately right-handed majority, but would not in
itself present an obstacle to conformity to any prevalent usage, or
to the influence of education. If then the preference of either hand
furnishes any index of the relative development of the two cerebral
hemispheres, what we may reasonably look for is a certain considerable
percentage of brains with the weight of the left hemisphere in
excess; a small percentage equally definitely characterised by the
preponderance in the right hemisphere; while in the average brain
the difference will be so slight as to be apt to escape observation.
It is further to be noted that if the habitual use of the right hand
tends in any degree to stimulate the development of the left cerebral
hemisphere, then the examples of strongly-marked cases of such must
greatly exceed those of the reverse type; since the left-handed man is
almost invariably ambidextrous, and so subjects both hemispheres to the
frequent stimulus of efferent nerve-force.
If the attention of physiologists devoted to cerebral investigations
is specially turned to the present aspect of research, cases of
well-marked left-handed patients, or what is manifestly of even
greater significance, of exceptionally dexterous right-handed patients,
in hospitals, asylums, and gaols, will from time to time present
themselves. It has indeed been affirmed that left-handedness prevails
among the “light-fingered” experts who find frequent lodging in our
gaols. The statement rests on no basis of statistical evidence;
but I can readily imagine that a left-handed pickpocket turning
his exceptional dexterity to account, might find at times the same
advantage that Ehud, the son of Gera the Benjamite, derived from using
the hand ordinarily recognised as passive or inert. As to the more
daring burglar, his sinister dexterity fills peaceful householders with
trepidation as soon as the rumour transpires of his presence in their
midst. In reality, however, the fancied prevalence of left-handedness
among savages, criminals, and idiots, is a mere reflex of the long
prevalent misconception that the preferential use of the left hand is
solely due to acquired habit, incurable awkwardness, and incapacity.
This is an idea that has often checked the development of exceptional
dexterity and a full command of both hands.
Meanwhile it is only in so far as the hand may prove to be an index
of the brain that observation is possible on the living subject. If
the transposition of the viscera, and the exceptional pressure of the
heart on the right, instead of the left side, were the source or the
unvarying concomitant of left-handedness this could be tested with
ease on the living subject. But the brain is beyond our reach; though
pathological phenomena, along with the results of vivisection in
the study of lower animal life, have thrown a flood of light on its
functions; as well as on the localisation of specific cerebrations in
their relation to sense, to language, and to general perceptions as
elements of mental action.
A monograph on left-handedness, ultimately printed in the _Proceedings
of the Royal Society of Canada for 1886_, was long delayed, in the hope
of meeting with some response to appeals I had repeatedly addressed
to medical friends, in the expectation that, sooner or later, some
strongly-marked case of left-handedness among hospital or other
patients might afford an opportunity for securing an autopsy of the
brain. But unless the fact has been previously noted, there is little
occasion in the passive condition of mortal disease to give prominence
to the left-handed action of a patient, and I had to rest content
with inviting attention to the subject when a favouring opportunity
presented itself. But my anticipations of the result to be looked for
were very definite, could the required organ of exceptionally developed
nerve-force be got hold of. There was indeed one very suitable brain
close at hand, and available for many curious speculative researches;
but wholly beyond reach of ocular investigation by me. I could
therefore only draw attention to it as possibly accessible to some
future investigator, since even vivisection must needs defeat my aim.
I accordingly remarked: “My own brain has now been in use for more
than the full allotted term of threescore years and ten, and the time
cannot be far distant when I shall be done with it. When that time
comes, I should be glad if it were turned to account for the little
further service of settling this physiological puzzle. If my ideas are
correct, I anticipate as the result of its examination that the right
hemisphere will not only be found to be heavier than the left, but that
it will probably be marked by a noticeable difference in the number and
arrangements of the convolutions.”
Happily since then the long-coveted opportunity has been afforded me.
In February 1887 I learned from Dr. Daniel Clark, Superintendent of
the Provincial Asylum at Toronto, of the death of Thomas Neilly, a
patient who had been under the doctor’s care for nearly two years. He
was a native of Ireland, had served in the army, and was there noted as
so inveterately left-handed that he was placed on the extreme left of
his company, and allowed the exceptional usage of firing from the left
shoulder. He could read and write, and was considered a man of good
intelligence, till he attained his thirty-fourth year, when symptoms
of insanity manifested themselves, and he was removed to the asylum,
where he died. My colleague, Professor Ramsay Wright, accompanied me to
the asylum on my learning of his death. The brain was removed and the
two hemispheres carefully weighed. Cerebral disease manifested itself
in the evidence of softening of the brain. But it was fully available
for the special inquiry; and the result of the testing experiment was
to place beyond doubt the preponderant weight of the right cerebral
hemisphere. No comprehensive inductions can be based on a single
case, but its confirmatory value is unmistakable at this stage of the
inquiry; and thus far it sustains the conclusions previously arrived
at, and justifies the assignment of the source of left-handedness to
an exceptional development of the right hemisphere of the brain; with
results of a greatly more comprehensive character, apparently affecting
the whole functions ordinarily located in the opposite cerebral
hemisphere.
THE END
_Printed by_ R. & R. CLARK, _Edinburgh_.