the skill that guides the work and the power that performs it are as
invisible as ever. I fear that not every listener took the
significance of those pregnant words in the passage I quoted from
John Bell,--“thinking to discover its properties in its form.” We have
discovered the working bee in this great hive of organization. We have
detected the cell in the very act of forming itself from a nucleus, of
transforming itself into various tissues, of selecting the elements of
various secretions. But why one cell becomes nerve and another muscle,
why one selects bile and another fat, we can no more pretend to tell,
than why one grape sucks out of the soil the generous juice which
princes hoard in their cellars, and another the wine which it takes
three men to drink,--one to pour it down, another to swallow it, and a
third to hold him while it is going down. Certain analogies between
this selecting power and the phenomena of endosmosis in the elective
affinities of chemistry we can find, but the problem of force remains
here, as everywhere, unsolved and insolvable.
Do we gain anything by attempting to get rid of the idea of a special
vital force because we find certain mutually convertible relations
between forces in the body and out of it? I think not, any more than we
should gain by getting rid of the idea and expression Magnetism because
of its correlation with electricity. We may concede the unity of all
forms of force, but we cannot overlook the fixed differences of its
manifestations according to the conditions under which it acts. It is a
mistake, however, to think the mystery is greater in an organized body
than in any other. We see a stone fall or a crystal form, and there is
nothing stranger left to wonder at, for we have seen the Infinite in
action.
Just so far as we can recognize the ordinary modes of operation of the
common forces of nature,--gravity, cohesion, elasticity, transudation,
chemical action, and the rest,--we see the so-called vital acts in
the light of a larger range of known facts and familiar analogies.
Matteuecci's well-remembered lectures contain many and striking examples
of the working of physical forces in physiological processes. Wherever
rigid experiment carries us, we are safe in following this lead; but
the moment we begin to theorize beyond our strict observation, we are in
danger of falling into those mechanical follies which true science has
long outgrown.
Recognizing the fact, then, that we have learned nothing but the
machinery of life, and are no nearer to its essence, what is it that we
have gained by this great discovery of the cell formation and function?
It would have been reward enough to learn the method Nature pursues
for its own sake. If the sovereign Artificer lets us into his own
laboratories and workshops, we need not ask more than the privilege
of looking on at his work. We do not know where we now stand in the
hierarchy of created intelligences. We were made a little lower than the
angels. I speak it not irreverently; as the lower animals surpass man
in some of their attributes, so it may be that not every angel's eye
can see as broadly and as deeply into the material works of God as
man himself, looking at the firmament through an equatorial of fifteen
inches' aperture, and searching into the tissues with a twelfth of an
inch objective.
But there are other positive gains of a more practical character. Thus
we are no longer permitted to place the seat of the living actions in
the extreme vessels, which are only the carriers from which each part
takes what it wants by the divine right of the omnipotent nucleated
cell. The organism has become, in the words already borrowed from
Virchow, “a sum of vital unities.” The strictum and laxum, the increased
and diminished action of the vessels, out of which medical theories
and methods of treatment have grown up, have yielded to the doctrine
of local cell-communities, belonging to this or that vascular district,
from which they help themselves, as contractors are wont to do from the
national treasury.
I cannot promise to do more than to select a few of the points of
contact between our ignorance and our knowledge which present particular
interest in the existing state of our physiological acquisitions.
Some of them involve the microscopic discoveries of which I have
been speaking, some belong to the domain of chemistry, and some have
relations with other departments of physical science.
If we should begin with the digestive function, we should find that the
long-agitated question of the nature of the acid of the gastric juice is
becoming settled in favor of the lactic. But the whole solvent agency of
the digestive fluid enters into the category of that exceptional mode of
action already familiar to us in chemistry as catalysis. It is therefore
doubly difficult of explanation; first, as being, like all reactions,
a fact not to be accounted for except by the imaginative appeal to
“affinity,” and secondly, as being one of those peculiar reactions
provoked by an element which stands outside and looks on without
compromising itself.
The doctrine of Mulder, so widely diffused in popular and scientific
belief, of the existence of a common base of all albuminous substances,
the so-called protein, has not stood the test of rigorous analysis. The
division of food into azotized and non-azotized is no doubt important,
but the attempt to show that the first only is plastic or nutritive,
while the second is simply calorifacient, or heat-producing, fails
entirely in the face of the facts revealed by the study of man in
different climates, and of numerous experiments in the feeding
of animals. I must return to this subject in connection with the
respiratory function.
The sugar-making faculty of the liver is another “catalytic” mystery, as
great as the rest of them, and no greater. Liver-tissue brings sugar out
of the blood, or out of its own substance;--why?
Quia est in eo
Virtus saccharitiva.
Just what becomes of the sugar beyond the fact of its disappearance
before it can get into the general circulation and sweeten our tempers,
it is hard to say.
The pancreatic fluid makes an emulsion of the fat contained in our food,
but just how the fatty particles get into the villi we must leave Brucke
and Kolliker to settle if they can.
No one has shown satisfactorily the process by which the
blood-corpuscles are formed out of the lymph-corpuscles, nor what
becomes of them. These two questions are like those famous household
puzzles,--Where do the flies come from? and, Where do the pins go to?
There is a series of organs in the body which has long puzzled
physiologists,--organs of glandular aspect, but having no ducts,--the
spleen, the thyroid and thymus bodies, and the suprarenal capsules. We
call them vascular glands, and we believe that they elaborate colored
and uncolored blood-cells; but just what changes they effect, and
just how they effect them, it has proved a very difficult matter to
determine. So of the noted glandules which form Peyer's patches, their
precise office, though seemingly like those of the lymphatic glands,
cannot be positively assigned, so far as I know, at the present time.
It is of obvious interest to learn it with reference to the pathology of
typhoid fever. It will be remarked that the coincidence of their changes
in this disease with enlargement of the spleen suggests the idea of a
similarity of function in these two organs.
The theories of the production of animal heat, from the times of Black,
Lavoisier, and Crawford to those of Liebig, are familiar to all who have
paid any attention to physiological studies. The simplicity of Liebig's
views, and the popular form in which they have been presented, have
given them wide currency, and incorporated them in the common belief and
language of our text-books. Direct oxidation or combustion of the carbon
and hydrogen contained in the food, or in the tissues themselves; the
division of alimentary substances into respiratory, or non-azotized,
and azotized,--these doctrines are familiar even to the classes in our
high-schools. But this simple statement is boldly questioned. Nothing
proves that oxygen combines (in the system) with hydrogen and carbon
in particular, rather than with sulphur and azote. Such is the
well-grounded statement of Robin and Verdeil. “It is very probable that
animal heat is entirely produced by the chemical actions which take
place in the organism, but the phenomenon is too complex to admit of our
calculating it according to the quality of oxygen consumed.” These last
are the words of Regnault, as cited by Mr. Lewes, whose intelligent
discussion of this and many of the most interesting physiological
problems I strongly recommend to your attention.
This single illustration covers a wider ground than the special function
to which it belongs. We are learning that the chemistry of the body must
be studied, not simply by its ingesta and egesta, but that there is a
long intermediate series of changes which must be investigated in their
own light, under their own special conditions. The expression “sum of
vital unities” applies to the chemical actions, as well as to other
actions localized in special parts; and when the distinguished chemists
whom I have just cited entitle their work a treatise on the immediate
principles of the body, they only indicate the nature of that
profound and subtile analysis which must take the place of all hasty
generalizations founded on a comparison of the food with residual
products.
I will only call your attention to the fact, that the exceptional
phenomenon of the laboratory is the prevailing law of the organism.
Nutrition itself is but one great catalytic process. As the blood
travels its rounds, each part selects its appropriate element and
transforms it to its own likeness. Whether the appropriating agent
be cell or nucleus, or a structureless solid like the intercellular
substance of cartilage, the fact of its presence determines the
separation of its proper constituents from the circulating fluid, so
that even when we are wounded bone is replaced by bone, skin by skin,
and nerve by nerve.
It is hardly without a smile that we resuscitate the old question of
the 'vis insita' of the muscular fibre, so famous in the discussions of
Haller and his contemporaries. Speaking generally, I think we may say
that Haller's doctrine is the one now commonly received; namely, that
the muscles contract in virtue of their own inherent endowments. It
is true that Kolliker says no perfectly decisive fact has been brought
forward to prove that the striated muscles contract without having been
acted on by nerves. Yet Mr. Bowman's observations on the contraction
of isolated fibres appear decisive enough (unless we consider them
invalidated by Dr. Lionel Beale's recent researches), tending to show
that each elementary fibre is supplied with nerves; and as to the
smooth muscular fibres, we have Virchow's statement respecting the
contractility of those of the umbilical cord, where there is not a trace
of any nerves.
In the investigation of the nervous system, anatomy and physiology have
gone hand in hand. It is very singular that so important, and seemingly
simple, a fact as the connection of the nerve-tubes, at their origin or
in their course, with the nerve-cells, should have so long remained open
to doubt, as you may see that it did by referring to the very complete
work of Sharpey and Quain (edition of 1849), the histological portion of
which is cordially approved by Kolliker himself.
Several most interesting points of the minute anatomy of the nervous
centres have been laboriously and skilfully worked out by a recent
graduate of this Medical School, in a monograph worthy to stand in line
with those of Lockhart Clarke, Stilling, and Schroder van der Kolk. I
have had the privilege of examining and of showing some of you a number
of Dr. Dean's skilful preparations. I have no space to give even an
abstract of his conclusions. I can only refer to his proof of the fact,
that a single cell may send its processes into several different bundles
of nerve-roots, and to his demonstration of the curved ascending and
descending fibres from the posterior nerveroots, to reach what he has
called the longitudinal columns of the cornea. I must also mention Dr.
Dean's exquisite microscopic photographs from sections of the medulla
oblongata, which appear to me to promise a new development, if not a new
epoch, in anatomical art.
It having been settled that the nerve-tubes can very commonly be traced
directly to the nerve-cells, the object of all the observers in this
department of anatomy is to follow these tubes to their origin. We have
an infinite snarl of telegraph wires, and we may be reasonably sure,
that, if we can follow them up, we shall find each of them ends in a
battery somewhere. One of the most interesting problems is to find the
ganglionic origin of the great nerves of the medulla oblongata, and this
is the end to which, by the aid of the most delicate sections, colored
so as to bring out their details, mounted so as to be imperishable,
magnified by the best instruments, and now self-recorded in the light
of the truth-telling sunbeam, our fellow-student is making a steady
progress in a labor which I think bids fair to rank with the most
valuable contributions to histology that we have had from this side of
the Atlantic.
It is interesting to see how old questions are incidentally settled in
the course of these new investigations. Thus, Mr. Clarke's dissections,
confirmed by preparations of Mr. Dean's which I have myself examined,
placed the fact of the decussation of the pyramids--denied by Haller, by
Morgagni, and even by Stilling--beyond doubt. So the spinal canal, the
existence of which, at least in the adult, has been so often disputed,
appears as a coarse and unequivocal anatomical fact in many of the
preparations referred to.
While these studies of the structure of the cord have been going on,
the ingenious and indefatigable Brown-Sequard has been investigating the
functions of its different parts with equal diligence. The microscopic
anatomists had shown that the ganglionic corpuscles of the gray matter
of the cord are connected with each other by their processes, as well
as with the nerve-roots. M. Brown-Sequard has proved by numerous
experiments that the gray substance transmits sensitive impressions and
muscular stimulation. The oblique ascending and descending fibres from
the posterior nerve-roots, joining the “longitudinal columns of the
cornua,” account for the results of Brown-Sequard's sections of the
posterior columns. The physiological experimenter has also made it
evident that the decussation of the conductors of sensitive impressions
has its seat in the spinal core, and not in the encephalon, as had been
supposed. Not less remarkable than these results are the facts, which
I with others of my audience have had the opportunity of observing, as
shown by M. Brown-Sequard, of the artificial production of epilepsy in
animals by injuring the spinal cord, and the induction of the paroxysm
by pinching a certain portion of the skin. I would also call the
student's attention to his account of the relations of the nervous
centres to nutrition and secretion, the last of which relations has been
made the subject of an extended essay by our fellow countryman, Dr. H.
F. Campbell of Georgia.
The physiology of the spinal cord seems a simple matter as you study it
in Longet. The experiments of Brown-Sequard have shown the problem to
be a complex one, and raised almost as many doubts as they have solved
questions; at any rate, I believe all lecturers on physiology agree that
there is no part of their task they dread so much as the analysis of the
evidence relating to the special offices of the different portions of
the medulla spinalis. In the brain we are sure that we do not know
how to localize functions; in the spinal cord, we think we do know
something; but there are so many anomalies, and seeming contradictions,
and sources of fallacy, that beyond the facts of crossed paralysis of
sensation, and the conducting agency of the gray substance, I am afraid
we retain no cardinal principles discovered since the development of the
reflex function took its place by Sir Charles Bell's great discovery.
By the manner in which I spoke of the brain, you will see that I am
obliged to leave phrenology sub Jove,--out in the cold,--as not one of
the household of science. I am not one of its haters; on the contrary, I
am grateful for the incidental good it has done. I love to amuse myself
in its plaster Golgothas, and listen to the glib professor, as he
discovers by his manipulations
“All that disgraced my betters met in me.”
I loved of old to see square-headed, heavy-jawed Spurzheim make a brain
flower out into a corolla of marrowy filaments, as Vieussens had done
before him, and to hear the dry-fibred but human-hearted George Combe
teach good sense under the disguise of his equivocal system. But the
pseudo-sciences, phrenology and the rest, seem to me only appeals to
weak minds and the weak points of strong ones. There is a pica or false
appetite in many intelligences; they take to odd fancies in place of
wholesome truth, as girls gnaw at chalk and charcoal. Phrenology juggles
with nature. It is so adjusted as to soak up all evidence that helps
it, and shed all that harms it. It crawls forward in all weathers, like
Richard Edgeworth's hygrometer. It does not stand at the boundary of our
ignorance, it seems to me, but is one of the will-o'-the-wisps of its
undisputed central domain of bog and quicksand. Yet I should not have
devoted so many words to it, did I not recognize the light it has thrown
on human actions by its study of congenital organic tendencies. Its maps
of the surface of the head are, I feel sure, founded on a delusion,
but its studies of individual character are always interesting and
instructive.
The “snapping-turtle” strikes after its natural fashion when it first
comes out of the egg. Children betray their tendencies in their way of
dealing with the breasts that nourish them; nay, lean venture to affirm,
that long before they are born they teach their mothers something of
their turbulent or quiet tempers.
“Castor gaudet equis, ovo proanatus eodem
Pugnis.”
Strike out the false pretensions of phrenology; call it anthropology;
let it study man the individual in distinction from man the abstraction,
the metaphysical or theological lay-figure; and it becomes “the proper
study of mankind,” one of the noblest and most interesting of pursuits.
The whole physiology of the nervous system, from the simplest
manifestation of its power in an insect up to the supreme act of the
human intelligence working through the brain, is full of the most
difficult yet profoundly interesting questions. The singular relations
between electricity and nerve-force, relations which it has been
attempted to interpret as meaning identity, in the face of palpable
differences, require still more extended studies. You may be interested
by Professor Faraday's statement of his opinion on the matter. “Though
I am not satisfied that the nervous fluid is only electricity, still I
think that the agent in the nervous system maybe an inorganic force; and
if there be reason for supposing that magnetism is a higher relation
of force than electricity, so it may well be imagined that the nervous
power may be of a still more exalted character, and yet within the reach
of experiment.”
In connection with this statement, it is interesting to refer to the
experiments of Helmholtz on the rapidity of transmission of the nervous
actions. The rate is given differently in Valentin's report of these
experiments and in that found in the “Scientific Annual” for 1858.
One hundred and eighty to three hundred feet per second is the rate
of movement assigned for sensation, but all such results must be very
vaguely approximative. Boxers, fencers, players at the Italian game
of morn, “prestidigitators,” and all who depend for their success on
rapidity of motion, know what differences there are in the personal
equation of movement.
Reflex action, the mechanical sympathy, if I may so call it, of distant
parts; Instinct, which is crystallized intelligence,--an absolute law
with its invariable planes and angles introduced into the sphere of
consciousness, as raphides are inclosed in the living cells of plants;
Intellect,--the operation of the thinking principle through material
organs, with an appreciable waste of tissue in every act of thought, so
that our clergymen's blood has more phosphates to get rid of on Monday
than on any other day of the week; Will,--theoretically the absolute
determining power, practically limited in different degrees by the
varying organization of races and individuals, annulled or perverted
by different ill-understood organic changes; on all these subjects our
knowledge is in its infancy, and from the study of some of them the
interdict of the Vatican is hardly yet removed.
I must allude to one or two points in the histology and physiology of
the organs of sense. The anterior continuation of the retina beyond
the ora serrata has been a subject of much discussion. If H. Muller and
Kolliker can be relied upon, this question is settled by recognizing
that a layer of cells, continued from the retina, passes over the
surface of the zonula Zinnii, but that no proper nervous element is so
prolonged forward.
I observe that Kolliker calls the true nervous elements of the retina
“the layer of gray cerebral substance.” In fact, the ganglionic
corpuscles of each eye may be considered as constituting a little brain,
connected with the masses behind by the commissure, commonly called the
optic nerve. We are prepared, therefore, to find these two little brains
in the most intimate relations with each other, as we find the cerebral
hemispheres. We know that they are directly connected by fibres that
arch round through the chiasma.
I mention these anatomical facts to introduce a physiological
observation of my own, first announced in one of the lectures before the
Medical Class, subsequently communicated to the American Academy of Arts
and Sciences, and printed in its “Transactions” for February 14, 1860.
I refer to the apparent transfer of impressions from one retina to
the other, to which I have given the name reflex vision. The idea was
suggested to me in consequence of certain effects noticed in employing
the stereoscope. Professor William B. Rodgers has since called the
attention of the American Scientific Association to some facts bearing
on the subject, and to a very curious experiment of Leonardo da Vinci's,
which enables the observer to look through the palm of his hand (or seem
to), as if it had a hole bored through it. As he and others hesitated
to accept my explanation, I was not sorry to find recently the following
words in the “Observations on Man” of that acute observer and thinker,
David Hartley. “An impression made on the right eye alone by a single
object may propagate itself into the left, and there raise up an image
almost equal in vividness to itself; and consequently when we see with
one eye only, we may, however, have pictures in both eyes.” Hartley,
in 1784, had anticipated many of the doctrines which have since been
systematized into the theory of reflex actions, and with which I have
attempted to associate this act of reflex vision. My sixth experiment,
however, in the communication referred to, appears to me to be a crucial
one, proving the correctness of my explanation, and I am not aware that
it has been before instituted.