November 1,
THE CRYSTALLINE LENS.?BY C. MACNAMARA.
1866.J
when distant
ORIGINAL COMMUNICATIONS.
to
MACNAMARA,
the Calcutta Ophthalmic Hospital.
In a former communication I described the arrangement of the contractile tissue in voluntary muscle, and remarked that it
'
appeared
to he
an
homogeneous substance,
its
properties
being to contract in obedience to the nervous force set in motion either by voluntary or reflex action. I observed that unstriped muscle afforded us one of the least complicated examples of contractile tissue, but the crystalline lens might with equal pro-
priety be considered as a muscle ; in fact, I had reasons for supposing the lens was capable of altering the curvature of its anterior surface, independently of the ciliary muscle; its fibrous bands being formed of contractile tissue, arranged in a peculiar The conmanner so that they might fulfil a special purpose. tractile tissue, whatever form it may present, performing the same functions, the disposition of its elements being simply adapted to the mechanical purposes for which it is required. It will be advisable, however, before proceeding further with this inquiry, to glance at the facts which prove that in the accommodation of the eye for near objects, the convexity of the anterior surface of the lens is increased; evidently some such changes in the dioptric media of the eye must take place, otherwise rays of light from a near object (divergent rays) could not possibly be brought to a focus on the retina, upon which rays from distant objects (parallel rays) are also focused; in other words, parallel and divergent rays cannot be brought to the same focus, unless the refractive media through which they pass is capable of altering its power of refraction. The necessary adjustment for the accommodation of the eye might be brought about by changes in the curvature of the cornea, or else by an elongation and contraction of the antero-posterior n-ris of the eyeball. "We may, however, dismiss these from our consideration, for Cramer and Helmholtz appear to have settled the matter in favour of an alteration in the curvature of the being the cause of the necessary changes in the dioptric
lens
media, for the correct focusing of parallel and divergent rays
on the retina. Helmholtz, in his experiments, took advantage of the well known fact that when a lighted candle is held in front of a healthy eye, three reflected images of the flame may be seen, apparently in the pupil, an anterior and posterior
image, being the reflections from the cornea and anterior surface of the lens, and a middle but inverted image reflected
erect
from the
posterior
ophthalmometer reflected images
surface of the lens or vitreous. "With his able to measure the magnitude of these under varying and he found
he
was
circumstances, long as the person under observation looked steadily at a distant object, that is, accommodated his eye for the far point, the three reflected figures of the flame of the candle remained unaltered in size; but the instant the accommodation of the eye was changed, and a near object was brought under observation, the reflected image from the anterior surface of the lens increased in magnitude, the other figures remaining unaltered in size. It became evident, therefore, in varying the accommodation of the eye from a far to a near object, that the convexity of the anterior surface of the lens is augmented, the breadth of the lens from before backwards being increased by the bulging forwards of its anterior surface. The amount of this that so
,
under
examination ; the lens in fact
therefore
a
convexity increases -when we look at acquiring a higher refractive power, less focal distance, so that divergent rays are
focused on the retina. The same conclusion has been arrived at by other means, but the above is sufficient for my purpose, which is to show that the antei-o-posterior axis of the lens
THE CRYSTALLINE LENS.
Surgeon
are
is then at rest, and its near objects, the lens thus and
By C.
objects
317
alteration in the curvature of the lens has been shown mathematically to be sufficient to bring divergent rays to the same focus, as parallel rays would be, if the curvature of the lens ?were diminished to the point to which it actually does recede
increases and diminishes during the accommodation of the eye for near and distant objects; the act is a voluntary one, inasmuch as our will controls the action. We wish to see a near object, and on looking at it the above described changes in the lens
place, in precisely the same way as the extensor muscles draw open the closed hand when we desire to open it. I would especially draw attention to the fact that these changes in the lens must be ever varying. So long as a person is awake, alterations in the curvature of the lens must be always taking
take
place,
as
every instant deviations in the distance from the
objects under observation must be going on, necessitating a corresponding alteration in the curvature of the lens ; for it has been proved, for correct vision, not only must rays of light be accurately focused on the retina, but that the rays must be brought to a focus absolutely and positively on its bacillary layer. It certainly seems to me more probable that these minute, constant, and marvellously rapid changes should be effected through some inherent power in the lens, rather than that a band of unstriped muscle, situated at a comparative distance from the lens, and which can only act on it through a secondary structure, should induce these changes in its form; nevertheless, the highest authorities of tho day hold that the accommodation of the eye is effected through the action of the " ciliary muscle. Donders says it therefore remains only to attribute to the musculus ciliares the important quality of accommodation muscle." But tho mechanism whereby the contraction of the little muscle alters the form of the lens, to however small a compass the question may now be reduced, is not yet satisfactorily and convincingly brought to light. It appears to me this question is far from being settled, nor can I concede this alleged power to the ciliary muscle; putting aside the fact that it is composed of unstriped muscle, which is usually uncontrollable by the will, it can only act through the suspensory ligament, which is reflected from the ciliary body on to the anterior surface of the capsule of tho lens; consequently, if the bulk of the ciliary body were to increase and diminish, the tension of the suspensory ligament would vary to a corresponding degree, and with it the accommodation of the eye, if this process depends on the tension or relaxation of the suspensory ligament: but we know the reverse of this is the case ; the vessels of the ciliary body are frequently congested, and the structure necessarily swollen, and yet the accommodation of the eye remains active. Again, the ciliary muscle may be divided, and the accommodation of the eye continue in perfect working order. Lastly, the whole of the iris has been torn away from its attachment, and therefore the ciliary muscle and elastic lamina of the choroid must have been seriously damaged, and yet the alterations above described in the lens have gone on as actively as ever, proving not only that so rude an injury could not destroy the accommodation of the as the lens remains in situ, but that these eye so long changes do not depend on the pressure of the iris on the lens as was at one time supposed. I maintain, therefore, although it has been shown that the anterior surface of the lens alters its convexity in accommodation, it has not been demonstrated that the ciliary muscle affects this change. It was a consideration of this position which led me to examine the subject more attentively, and to ask myself the question?what then can be the meaning of the complex arrangement of the lens fibres, unless they have power
retina of
to alter the curvature of its anterior surface ? The answer to of the kind would perhaps strike many persons as a
problem
THE INDIAN MEDICAL GAZETTE.
318
simple enough, there being no apparent connexion between "flattened, riband-like, albuminous fibres" of the lens with voluntary muscle; but strip a muscle of its nerves, vessels, and fibrous tissue, and what remains but an homogeneous sarcous case, and a vast multitude of longitudinal and transverse bands of an homogeneous substance, which I propose to call conthe
tractile tissue. "With these facts before us, we may proceed to show that in reality there is a strong analogy between the fibres of the lens and the essential and characteristic elements of voluntary muscle; there are indications of the same arrangement of longitudinal and transverse bands in the one as in the other, but from the nature of its functions it would be impossible to admit blood vessels and connective tissue into the substance of the lens, and these in fact are merely accessory tissue, and no more a part of muscle than they are of bone. The observations I have
to the lower orders of have I been able as yet to satisfy myself that a similar condition exists in the human lens; but the difficulty of procuring perfectly fresh and healthy specimens to detail have been the
vertebrata,
principally confined
nor
from the eye of a human being is almost an insuperable difficulty in a matter of this kind, nevertheless the fibrous bands of which it is composed undoubtedly do possess indications of a structure similar to that of the lower orders of the vertebrata, and further researches will probably clear up apparent differences between the two. ed
The animal to be examined has been killed, and its body treatstrictly according to the rules laid down by Dr. Bealo for the of tissues to be examined under
high powers, and preparation subsequently the leas and its capsule have been removed, and allowed to soak in Price's glycerine for a month, when it is ready for examination. The capsule having been opened, the lens looks very much like a small ball of cotton; it is to he rolled on to a slide, and a few of its fibres carefully detached glass
and allowed to fall into
a
drop
of
glycerine; they
must not be
disturbed more than can possibly be avoided; as they are removed from the lens, so let them lie, and then gently allow the glass cover to fall over them; it should not be pressed on the
objects, but simply rest on them;
the preparation is then There an inch glass.
examination under the fiftieth of
ready for are
one
points, however, which require attention with regard to the management of the microscope, the aperture through which light is admitted to the condenser can hardly be too small, and the condenser must be moved up and down on its stage so as to vary its focus as much as that of the adjustment screw of the microscope. If these points are attended to, we shall discover that the lens fibres may be divided into two classes, one being flattened bands of apparently homogeneous tissue with serrated edges, and the other fibres having a distinct and clearly defined outline, within which are apparently perpendicular and horizontal bands of contractile tissue, analogous to those I have described in the primitive fibres of voluntary muscle; they are, however, far less distinct, and in fact most difficult to define ; but after numerous examinations, varied in every conceivable way, I believe an arrangement of the kind does exist. The relation or
two
between these two sets of fibres is as follows: the flattened serrated band is a detached and altered lens fibre, its normal condition having been that of a fibre with definite outline and internal structure, but having been detached or injured, the con-
has been broken through, and the fibre spreads out into a flattened and serrated band. Each fibre is condensed and harder towards either extremity; in the middle of its course it is flattened and softer, and therefore more easily
taining
case
so that we frequently meet with fibres in which the central portion presents a flattened and serrated appearance, having been injured, while either extremity may be a perfect fibre with a dark outline, and having indications of transverse and longitudinal bands within it; if the striated extremity of such a fibre be kept in the field of.,the microscope, and the
destroyed,
fiftieth, of
an
glass,
we
[November 1,
1866.
inch lens is
gently screwed down on the covering increase the pressure the outline of the fibre bursts open, its structure disappears, and its remains present the appearance of a flattened, serrated band; we have in fact as
by
pressure destroyed the structure of the fibre, and the remnant of its complicated anatomy lies before us as a squashed and distorted band. The lens is made up of layers of these remarks, like the leaves of an
fibres, arranged, as onion, one over the other; ro they might be likened to the primitive fibres of voluntary muscle, arranged in layers, consisting of a pile of fibres forming the thickness of the layer, while its breadth is constituted of a multitude of such piles arranged side by side ; the integrity of the whole, however, are intimately connected, and dependent one on the other. Each fibre is contained in an homogeneous case, within which are longitudinal bands running Mr. Bowman
from
one
end of the fibre to the other end, and these
are
con-
by transverse bands with spaces between them. It would seem, however, as if the containing case (or some other force) confines the elastic, internal structures of the fibre within certain bounds, for the moment it is destroyed the fibre expands
nected
into
a
posing
serrated band.
It has often occurred to
the central
of the band
part
its toothed
me that supto contract on itself, open out and separate from enclosed in a case of homowere
edges must necessarily another, and if the whole were geneous tissue, we should have an appearance produced similar to that which actually exists. I have already mentioned that one
in
an examination of this kind it is very necessary not to make pressure on the glass cover over the objects, or to disturb the fibres more than can possibly bo avoided before they are brought into the field of the microscope. The meaning of this must now be apparent; for if one pile of fibres is tern away from another, the relation of the whole of the individual fibres the
Composing destroyed. This is the great difficulty we examining the fibres of the lens; it requires considerable patience to enable us to meet with them in their normal condition, and when once their outline has been broken through, and they have become serrated bands, they I am perfectly aware that never return to their normal state. observations of this kind are of an intricate nature ; dissecting a fibre under a glass magnifying 2800 diameter, must necessarily pile
will
have
probably
be
to contend with in
make me diffident as to the conclusions arrived at, nevertheless the ideas above given have forced themselves on my mind after
study. They seem to me to open out an extensive enquiry for if carried to their legitimate results, with the aid of powers higher than any yet made, they must tend towards the solution of that great problem, the connection between the nerves and voluntary muscle. There cannot be a doubt that it is directly upon the contractile tissue of muscle careful
field of
,
that the nervous force acts, and till the circumstances of the former are understood, we cannot possibly expect to master the details of the latter. It is the apparent analogy between the minute structure of the ultimate of fibre of muscle and those of the lens which first led me to believe the lens is capable of altering the curvature of its
surface, independently of the ciliary muscle. I have capsule of the lens, and there is no to suppose they do not enter its substance, if their pre-
anterior
traced nerves over the reason sence
there is necessary, of which
we
have
no
evidence.
The
germinal matter lining the capsule of the lens is probably sufficient to produce its formed material, and in the growing lens I have found germinal matter scattered throughout its substance, so that there are really no elements in striped muscle not to be found in the lens, except blood vessels and connective tissuet and these, from the nature and functions of the lens, could no,
be admitted into its substance ; moreover, they form no part ofthe essential element of muscle. If this be the case, and if it has been proved that the lens dilates and contracts, in obedience to a effort, in exactly the same way that striped muscle
voluntary
November 1, 1866.]
ON THE DETECTION OF DHATOORA.?BY W. J. PALMER.
does, surely it is far more reasonable" to suppose that these changes are effected through an inherent power residing in the lens, analogous to that which exists in voluntary muscle, rather than to fall hack upon the ciliary muscle as being the active agent in the accommodation of the eye. Preconceived opinions as to the nature of muscular fibre must, I think, be revised, and in fact the contractile tissue theory introduces us to an entirely new field of physiological research : time and patient study alone can test its value, and bring us to a safe conclusion on the subject. I do not overlook the fact that to complete my account of the lens, I should have tested its powers (when removed from the eye) of expanding under the influence of an electric current; I made one attempt in this direction, but the means at my command are wanting in delicacy and precision, without which it is impossible to carry on investigations of this kind.
319
THE CRYSTALLINE LENS.?BY C. MACNAMARA.
1866.J
when distant
ORIGINAL COMMUNICATIONS.
to
MACNAMARA,
the Calcutta Ophthalmic Hospital.
In a former communication I described the arrangement of the contractile tissue in voluntary muscle, and remarked that it
'
appeared
to he
an
homogeneous substance,
its
properties
being to contract in obedience to the nervous force set in motion either by voluntary or reflex action. I observed that unstriped muscle afforded us one of the least complicated examples of contractile tissue, but the crystalline lens might with equal pro-
priety be considered as a muscle ; in fact, I had reasons for supposing the lens was capable of altering the curvature of its anterior surface, independently of the ciliary muscle; its fibrous bands being formed of contractile tissue, arranged in a peculiar The conmanner so that they might fulfil a special purpose. tractile tissue, whatever form it may present, performing the same functions, the disposition of its elements being simply adapted to the mechanical purposes for which it is required. It will be advisable, however, before proceeding further with this inquiry, to glance at the facts which prove that in the accommodation of the eye for near objects, the convexity of the anterior surface of the lens is increased; evidently some such changes in the dioptric media of the eye must take place, otherwise rays of light from a near object (divergent rays) could not possibly be brought to a focus on the retina, upon which rays from distant objects (parallel rays) are also focused; in other words, parallel and divergent rays cannot be brought to the same focus, unless the refractive media through which they pass is capable of altering its power of refraction. The necessary adjustment for the accommodation of the eye might be brought about by changes in the curvature of the cornea, or else by an elongation and contraction of the antero-posterior n-ris of the eyeball. "We may, however, dismiss these from our consideration, for Cramer and Helmholtz appear to have settled the matter in favour of an alteration in the curvature of the being the cause of the necessary changes in the dioptric
lens
media, for the correct focusing of parallel and divergent rays
on the retina. Helmholtz, in his experiments, took advantage of the well known fact that when a lighted candle is held in front of a healthy eye, three reflected images of the flame may be seen, apparently in the pupil, an anterior and posterior
image, being the reflections from the cornea and anterior surface of the lens, and a middle but inverted image reflected
erect
from the
posterior
ophthalmometer reflected images
surface of the lens or vitreous. "With his able to measure the magnitude of these under varying and he found
he
was
circumstances, long as the person under observation looked steadily at a distant object, that is, accommodated his eye for the far point, the three reflected figures of the flame of the candle remained unaltered in size; but the instant the accommodation of the eye was changed, and a near object was brought under observation, the reflected image from the anterior surface of the lens increased in magnitude, the other figures remaining unaltered in size. It became evident, therefore, in varying the accommodation of the eye from a far to a near object, that the convexity of the anterior surface of the lens is augmented, the breadth of the lens from before backwards being increased by the bulging forwards of its anterior surface. The amount of this that so
,
under
examination ; the lens in fact
therefore
a
convexity increases -when we look at acquiring a higher refractive power, less focal distance, so that divergent rays are
focused on the retina. The same conclusion has been arrived at by other means, but the above is sufficient for my purpose, which is to show that the antei-o-posterior axis of the lens
THE CRYSTALLINE LENS.
Surgeon
are
is then at rest, and its near objects, the lens thus and
By C.
objects
317
alteration in the curvature of the lens has been shown mathematically to be sufficient to bring divergent rays to the same focus, as parallel rays would be, if the curvature of the lens ?were diminished to the point to which it actually does recede
increases and diminishes during the accommodation of the eye for near and distant objects; the act is a voluntary one, inasmuch as our will controls the action. We wish to see a near object, and on looking at it the above described changes in the lens
place, in precisely the same way as the extensor muscles draw open the closed hand when we desire to open it. I would especially draw attention to the fact that these changes in the lens must be ever varying. So long as a person is awake, alterations in the curvature of the lens must be always taking
take
place,
as
every instant deviations in the distance from the
objects under observation must be going on, necessitating a corresponding alteration in the curvature of the lens ; for it has been proved, for correct vision, not only must rays of light be accurately focused on the retina, but that the rays must be brought to a focus absolutely and positively on its bacillary layer. It certainly seems to me more probable that these minute, constant, and marvellously rapid changes should be effected through some inherent power in the lens, rather than that a band of unstriped muscle, situated at a comparative distance from the lens, and which can only act on it through a secondary structure, should induce these changes in its form; nevertheless, the highest authorities of tho day hold that the accommodation of the eye is effected through the action of the " ciliary muscle. Donders says it therefore remains only to attribute to the musculus ciliares the important quality of accommodation muscle." But tho mechanism whereby the contraction of the little muscle alters the form of the lens, to however small a compass the question may now be reduced, is not yet satisfactorily and convincingly brought to light. It appears to me this question is far from being settled, nor can I concede this alleged power to the ciliary muscle; putting aside the fact that it is composed of unstriped muscle, which is usually uncontrollable by the will, it can only act through the suspensory ligament, which is reflected from the ciliary body on to the anterior surface of the capsule of tho lens; consequently, if the bulk of the ciliary body were to increase and diminish, the tension of the suspensory ligament would vary to a corresponding degree, and with it the accommodation of the eye, if this process depends on the tension or relaxation of the suspensory ligament: but we know the reverse of this is the case ; the vessels of the ciliary body are frequently congested, and the structure necessarily swollen, and yet the accommodation of the eye remains active. Again, the ciliary muscle may be divided, and the accommodation of the eye continue in perfect working order. Lastly, the whole of the iris has been torn away from its attachment, and therefore the ciliary muscle and elastic lamina of the choroid must have been seriously damaged, and yet the alterations above described in the lens have gone on as actively as ever, proving not only that so rude an injury could not destroy the accommodation of the as the lens remains in situ, but that these eye so long changes do not depend on the pressure of the iris on the lens as was at one time supposed. I maintain, therefore, although it has been shown that the anterior surface of the lens alters its convexity in accommodation, it has not been demonstrated that the ciliary muscle affects this change. It was a consideration of this position which led me to examine the subject more attentively, and to ask myself the question?what then can be the meaning of the complex arrangement of the lens fibres, unless they have power
retina of
to alter the curvature of its anterior surface ? The answer to of the kind would perhaps strike many persons as a
problem
THE INDIAN MEDICAL GAZETTE.
318
simple enough, there being no apparent connexion between "flattened, riband-like, albuminous fibres" of the lens with voluntary muscle; but strip a muscle of its nerves, vessels, and fibrous tissue, and what remains but an homogeneous sarcous case, and a vast multitude of longitudinal and transverse bands of an homogeneous substance, which I propose to call conthe
tractile tissue. "With these facts before us, we may proceed to show that in reality there is a strong analogy between the fibres of the lens and the essential and characteristic elements of voluntary muscle; there are indications of the same arrangement of longitudinal and transverse bands in the one as in the other, but from the nature of its functions it would be impossible to admit blood vessels and connective tissue into the substance of the lens, and these in fact are merely accessory tissue, and no more a part of muscle than they are of bone. The observations I have
to the lower orders of have I been able as yet to satisfy myself that a similar condition exists in the human lens; but the difficulty of procuring perfectly fresh and healthy specimens to detail have been the
vertebrata,
principally confined
nor
from the eye of a human being is almost an insuperable difficulty in a matter of this kind, nevertheless the fibrous bands of which it is composed undoubtedly do possess indications of a structure similar to that of the lower orders of the vertebrata, and further researches will probably clear up apparent differences between the two. ed
The animal to be examined has been killed, and its body treatstrictly according to the rules laid down by Dr. Bealo for the of tissues to be examined under
high powers, and preparation subsequently the leas and its capsule have been removed, and allowed to soak in Price's glycerine for a month, when it is ready for examination. The capsule having been opened, the lens looks very much like a small ball of cotton; it is to he rolled on to a slide, and a few of its fibres carefully detached glass
and allowed to fall into
a
drop
of
glycerine; they
must not be
disturbed more than can possibly be avoided; as they are removed from the lens, so let them lie, and then gently allow the glass cover to fall over them; it should not be pressed on the
objects, but simply rest on them;
the preparation is then There an inch glass.
examination under the fiftieth of
ready for are
one
points, however, which require attention with regard to the management of the microscope, the aperture through which light is admitted to the condenser can hardly be too small, and the condenser must be moved up and down on its stage so as to vary its focus as much as that of the adjustment screw of the microscope. If these points are attended to, we shall discover that the lens fibres may be divided into two classes, one being flattened bands of apparently homogeneous tissue with serrated edges, and the other fibres having a distinct and clearly defined outline, within which are apparently perpendicular and horizontal bands of contractile tissue, analogous to those I have described in the primitive fibres of voluntary muscle; they are, however, far less distinct, and in fact most difficult to define ; but after numerous examinations, varied in every conceivable way, I believe an arrangement of the kind does exist. The relation or
two
between these two sets of fibres is as follows: the flattened serrated band is a detached and altered lens fibre, its normal condition having been that of a fibre with definite outline and internal structure, but having been detached or injured, the con-
has been broken through, and the fibre spreads out into a flattened and serrated band. Each fibre is condensed and harder towards either extremity; in the middle of its course it is flattened and softer, and therefore more easily
taining
case
so that we frequently meet with fibres in which the central portion presents a flattened and serrated appearance, having been injured, while either extremity may be a perfect fibre with a dark outline, and having indications of transverse and longitudinal bands within it; if the striated extremity of such a fibre be kept in the field of.,the microscope, and the
destroyed,
fiftieth, of
an
glass,
we
[November 1,
1866.
inch lens is
gently screwed down on the covering increase the pressure the outline of the fibre bursts open, its structure disappears, and its remains present the appearance of a flattened, serrated band; we have in fact as
by
pressure destroyed the structure of the fibre, and the remnant of its complicated anatomy lies before us as a squashed and distorted band. The lens is made up of layers of these remarks, like the leaves of an
fibres, arranged, as onion, one over the other; ro they might be likened to the primitive fibres of voluntary muscle, arranged in layers, consisting of a pile of fibres forming the thickness of the layer, while its breadth is constituted of a multitude of such piles arranged side by side ; the integrity of the whole, however, are intimately connected, and dependent one on the other. Each fibre is contained in an homogeneous case, within which are longitudinal bands running Mr. Bowman
from
one
end of the fibre to the other end, and these
are
con-
by transverse bands with spaces between them. It would seem, however, as if the containing case (or some other force) confines the elastic, internal structures of the fibre within certain bounds, for the moment it is destroyed the fibre expands
nected
into
a
posing
serrated band.
It has often occurred to
the central
of the band
part
its toothed
me that supto contract on itself, open out and separate from enclosed in a case of homowere
edges must necessarily another, and if the whole were geneous tissue, we should have an appearance produced similar to that which actually exists. I have already mentioned that one
in
an examination of this kind it is very necessary not to make pressure on the glass cover over the objects, or to disturb the fibres more than can possibly bo avoided before they are brought into the field of the microscope. The meaning of this must now be apparent; for if one pile of fibres is tern away from another, the relation of the whole of the individual fibres the
Composing destroyed. This is the great difficulty we examining the fibres of the lens; it requires considerable patience to enable us to meet with them in their normal condition, and when once their outline has been broken through, and they have become serrated bands, they I am perfectly aware that never return to their normal state. observations of this kind are of an intricate nature ; dissecting a fibre under a glass magnifying 2800 diameter, must necessarily pile
will
have
probably
be
to contend with in
make me diffident as to the conclusions arrived at, nevertheless the ideas above given have forced themselves on my mind after
study. They seem to me to open out an extensive enquiry for if carried to their legitimate results, with the aid of powers higher than any yet made, they must tend towards the solution of that great problem, the connection between the nerves and voluntary muscle. There cannot be a doubt that it is directly upon the contractile tissue of muscle careful
field of
,
that the nervous force acts, and till the circumstances of the former are understood, we cannot possibly expect to master the details of the latter. It is the apparent analogy between the minute structure of the ultimate of fibre of muscle and those of the lens which first led me to believe the lens is capable of altering the curvature of its
surface, independently of the ciliary muscle. I have capsule of the lens, and there is no to suppose they do not enter its substance, if their pre-
anterior
traced nerves over the reason sence
there is necessary, of which
we
have
no
evidence.
The
germinal matter lining the capsule of the lens is probably sufficient to produce its formed material, and in the growing lens I have found germinal matter scattered throughout its substance, so that there are really no elements in striped muscle not to be found in the lens, except blood vessels and connective tissuet and these, from the nature and functions of the lens, could no,
be admitted into its substance ; moreover, they form no part ofthe essential element of muscle. If this be the case, and if it has been proved that the lens dilates and contracts, in obedience to a effort, in exactly the same way that striped muscle
voluntary
November 1, 1866.]
ON THE DETECTION OF DHATOORA.?BY W. J. PALMER.
does, surely it is far more reasonable" to suppose that these changes are effected through an inherent power residing in the lens, analogous to that which exists in voluntary muscle, rather than to fall hack upon the ciliary muscle as being the active agent in the accommodation of the eye. Preconceived opinions as to the nature of muscular fibre must, I think, be revised, and in fact the contractile tissue theory introduces us to an entirely new field of physiological research : time and patient study alone can test its value, and bring us to a safe conclusion on the subject. I do not overlook the fact that to complete my account of the lens, I should have tested its powers (when removed from the eye) of expanding under the influence of an electric current; I made one attempt in this direction, but the means at my command are wanting in delicacy and precision, without which it is impossible to carry on investigations of this kind.
319
