significance for the subtle thinker, to whom we owe both the
spiritualistic and the materialistic philosophies of modern times. It
was in the very year of its publication, 1628, that Descartes withdrew
into that life of solitary investigation and meditation of which his
philosophy was the fruit. And, as the course of his speculations
led him to establish an absolute distinction of nature between the
material and the mental worlds, he was logically compelled to seek
for the explanation of the phenomena of the material world within
itself; and having allotted the realm of thought to the soul, to see
nothing but extension and motion in the rest of nature. Descartes uses
“thought” as the equivalent of our modern term “consciousness.” Thought
is the function of the soul, and its only function. Our natural heat
and all the movements of the body, says he, do not depend on the soul.
Death does not take place from any fault of the soul, but only because
some of the principal parts of the body become corrupted. The body of a
living man differs from that of a dead man in the same way as a watch
or other automaton (that is to say, a machine which moves of itself)
when it is wound up and has, in itself, the physical principle of the
movements which the mechanism is adapted to perform, differs from the
same watch, or other machine, when it is broken, and the physical
principle of its movement no longer exists. All the actions which are
common to us and the lower animals depend only on the conformation of
our organs, and the course which the animal spirits take in the brain,
the nerves, and the muscles; in the same way as the movement of a watch
is produced by nothing but the force of its spring and the figure of
its wheels and other parts.
Descartes’ “Treatise on Man” is a sketch of human physiology, in which
a bold attempt is made to explain all the phenomena of life, except
those of consciousness, by physical reasonings. To a mind turned in
this direction, Harvey’s exposition of the heart and vessels as a
hydraulic mechanism must have been supremely welcome.
Descartes was not a mere philosophical theorist, but a hardworking
dissector and experimenter, and he held the strongest opinion
respecting the practical value of the new conception which he was
introducing. He speaks of the importance of preserving health, and of
the dependence of the mind on the body being so close that, perhaps,
the only way of making men wiser and better than they are, is to be
sought in medical science. “It is true,” says he, “that as medicine
is now practised, it contains little that is very useful; but without
any desire to depreciate, I am sure that there is no one, even among
professional men, who will not declare that all we know is very little
as compared with that which remains to be known; and that we might
escape an infinity of diseases of the mind, no less than of the body,
and even perhaps from the weakness of old age, if we had sufficient
knowledge of their causes, and of all the remedies with which nature
has provided us.”[96] So strongly impressed was Descartes with this,
that he resolved to spend the rest of his life in trying to acquire
such a knowledge of nature as would lead to the construction of a
better medical doctrine.[97] The anti-Cartesians found material for
cheap ridicule in these aspirations of the philosopher; and it is
almost needless to say that, in the thirteen years which elapsed
between the publication of the “Discours” and the death of Descartes,
he did not contribute much to their realisation. But, for the next
century, all progress in physiology took place along the lines which
Descartes laid down.
The greatest physiological and pathological work of the seventeenth
century, Borelli’s treatise “De Motu Animalium,” is, to all intents
and purposes, a development of Descartes’ fundamental conception; and
the same may be said of the physiology and pathology of Boerhaave,
whose authority dominated in the medical world of the first half of the
eighteenth century.
With the origin of modern chemistry, and of electrical science, in the
latter half of the eighteenth century, aids in the analysis of the
phenomena of life, of which Descartes could not have dreamed, were
offered to the physiologist. And the greater part of the gigantic
progress which has been made in the present century is a justification
of the prevision of Descartes. For it consists, essentially, in a more
and more complete resolution of the grosser organs of the living body
into physico-chemical mechanisms.
“I shall try to explain our whole bodily machinery in such a way, that
it will be no more necessary for us to suppose that the soul produces
such movements as are not voluntary, than it is to think that there is
in a clock a soul which causes it to show the hours.”[98] These words
of Descartes might be appropriately taken as a motto by the author of
any modern treatise on physiology.
But though, as I think, there is no doubt that Descartes was the
first to propound the fundamental conception of the living body as
a physical mechanism, which is the distinctive feature of modern,
as contrasted with ancient physiology, he was misled by the natural
temptation to carry out, in all its details, a parallel between the
machines with which he was familiar, such as clocks and pieces of
hydraulic apparatus, and the living machine. In all such machines there
is a central source of power, and the parts of the machine are merely
passive distributors of that power. The Cartesian school conceived
of the living body as a machine of this kind; and herein they might
have learned from Galen, who, whatever ill use he may have made of the
doctrine of “natural faculties,” nevertheless had the great merit of
perceiving that local forces play a great part in physiology.
The same truth was recognised by Glisson, but it was first prominently
brought forward in the Hallerian doctrine of the “vis insita” of
muscles. If muscle can contract without nerve, there is an end of the
Cartesian mechanical explanation of its contraction by the influx of
animal spirits.
The discoveries of Trembley tended in the same direction. In the
freshwater _Hydra_, no trace was to be found of that complicated
machinery upon which the performance of the functions in the higher
animals was supposed to depend. And yet the hydra moved, fed, grew,
multiplied, and its fragments exhibited all the powers of the whole.
And, finally, the work of Caspar F. Wolff,[99] by demonstrating the
fact that the growth and development of both plants and animals take
place antecedently to the existence of their grosser organs, and are,
in fact, the causes and not the consequences of organisation (as then
understood), sapped the foundations of the Cartesian physiology as a
complete expression of vital phenomena.
For Wolff, the physical basis of life is a fluid, possessed of a “vis
essentialis” and a “solidescibilitas,” in virtue of which it gives rise
to organisation; and, as he points out, this conclusion strikes at the
root of the whole iatro-mechanical system.
In this country, the great authority of John Hunter exerted a similar
influence; though it must be admitted that the too sibylline utterances
which are the outcome of Hunter’s struggles to define his conceptions
are often susceptible of more than one interpretation. Nevertheless,
on some points Hunter is clear enough. For example, he is of opinion
that “Spirit is only a property of matter” (“Introduction to Natural
History,” p. 6), he is prepared to renounce animism (_l.c._ p. 8),
and his conception of life is so completely physical that he thinks
of it as something which can exist in a state of combination in the
food. “The aliment we take in has in it, in a fixed state, the real
life; and this does not become active until it has got into the lungs;
for there it is freed from its prison” (“Observations on Physiology,”
p. 113). He also thinks that “It is more in accord with the general
principles of the animal machine to suppose that none of its effects
are produced from any mechanical principle whatever; and that every
effect is produced from an action in the part; which action is produced
by a stimulus upon the part which acts, or upon some other part with
which this part sympathises so as to take up the whole action” (_l.c._
p. 152).
And Hunter is as clear as Wolff, with whose work he was probably
unacquainted, that “whatever life is, it most certainly does not depend
upon structure or organisation” (_l.c._ p. 114).
Of course it is impossible that Hunter could have intended to deny
the existence of purely mechanical operations in the animal body.
But while, with Borelli and Boerhaave, he looked upon absorption,
nutrition, and secretion as operations effected by means of the small
vessels, he differed from the mechanical physiologists, who regarded
these operations as the result of the mechanical properties of the
small vessels, such as the size, form, and disposition of their canals
and apertures. Hunter, on the contrary, considers them to be the effect
of properties of these vessels which are not mechanical but vital. “The
vessels,” says he, “have more of the polypus in them than any other
part of the body,” and he talks of the “living and sensitive principles
of the arteries,” and even of the “dispositions or feelings of the
arteries.” “When the blood is good and genuine the sensations of the
arteries, or the dispositions for sensation, are agreeable.... It is
then they dispose of the blood to the best advantage, increasing the
growth of the whole, supplying any losses, keeping up a due succession,
etc.” (_l.c._ p. 133).
If we follow Hunter’s conceptions to their logical issue, the life of
one of the higher animals is essentially the sum of the lives of all
the vessels, each of which is a sort of physiological unit, answering
to a polype; and, as health is the result of the normal “action of the
vessels,” so is disease an effect of their abnormal action. Hunter thus
stands in thought, as in time, midway between Borelli on the one hand,
and Bichat on the other.
The acute founder of general anatomy, in fact, outdoes Hunter in his
desire to exclude physical reasonings from the realm of life. Except in
the interpretation of the action of the sense organs, he will not allow
physics to have anything to do with physiology.
“To apply the physical sciences to physiology is to explain the
phenomena of living bodies by the laws of inert bodies. Now this
is a false principle, hence all its consequences are marked with
the same stamp. Let us leave to chemistry its affinity; to physics,
its elasticity and its gravity. Let us invoke for physiology only
sensibility and contractility.”[100]
Of all the unfortunate dicta of men of eminent ability this seems
one of the most unhappy, when we think of what the application of
the methods and the data of physics and chemistry has done towards
bringing physiology into its present state. It is not too much to say
that one half of a modern text-book of physiology consists of applied
physics and chemistry; and that it is exactly in the exploration of the
phenomena of sensibility and contractility that physics and chemistry
have exerted the most potent influence.
Nevertheless, Bichat rendered a solid service to physiological progress
by insisting upon the fact that what we call life, in one of the higher
animals, is not an indivisible unitary archæus dominating, from its
central seat, the parts of the organism, but a compound result of the
synthesis of the separate lives of those parts.
“All animals,” says he, “are assemblages of different organs, each of
which performs its function and concurs, after its fashion, in the
preservation of the whole. They are so many special machines in the
general machine which constitutes the individual. But each of these
special machines is itself compounded of many tissues of very different
natures, which in truth constitute the elements of those organs”
(_l.c._ lxxix.) “The conception of a proper vitality is applicable only
to these simple tissues, and not to the organs themselves” (_l.c._
lxxxiv.)
And Bichat proceeds to make the obvious application of this doctrine of
synthetic life, if I may so call it, to pathology. Since diseases are
only alterations of vital properties, and the properties of each tissue
are distinct from those of the rest, it is evident that the diseases of
each tissue must be different from those of the rest. Therefore, in any
organ composed of different tissues, one may be diseased and the other
remain healthy; and this is what happens in most cases (_l.c._ lxxxv.)
In a spirit of true prophecy, Bichat says, “We have arrived at an
epoch, in which pathological anatomy should start afresh.” For, as the
analysis of the organs had led him to the tissues, as the physiological
units of the organism; so, in a succeeding generation, the analysis
of the tissues led to the cell as the physiological element of the
tissues. The contemporaneous study of development brought out the same
result; and the zoologists and botanists, exploring the simplest and
the lowest forms of animated beings, confirmed the great induction of
the cell theory. Thus the apparently opposed views, which have been
battling with one another ever since the middle of the last century,
have proved to be each half the truth.
The proposition of Descartes that the body of a living man is a
machine, the actions of which are explicable by the known laws of
matter and motion, is unquestionably largely true. But it is also
true, that the living body is a synthesis of innumerable physiological
elements, each of which may nearly be described, in Wolff’s words, as a
fluid possessed of a “vis essentialis,” and a “solidescibilitas”; or,
in modern phrase, as protoplasm susceptible of structural metamorphosis
and functional metabolism: and that the only machinery, in the precise
sense in which the Cartesian school understood mechanism, is, that
which co-ordinates and regulates these physiological units into an
organic whole.
In fact, the body is a machine of the nature of an army, not of that
of a watch or of a hydraulic apparatus. Of this army each cell is a
soldier, an organ a brigade, the central nervous system headquarters
and field telegraph, the alimentary and circulatory system the
commissariat. Losses are made good by recruits born in camp, and the
life of the individual is a campaign, conducted successfully for a
number of years, but with certain defeat in the long run.
The efficacy of an army, at any given moment, depends on the health of
the individual soldier, and on the perfection of the machinery by which
he is led and brought into action at the proper time; and, therefore,
if the analogy holds good, there can be only two kinds of diseases, the
one dependent on abnormal states of the physiological units, the other
on perturbations of their co-ordinating and alimentative machinery.
Hence, the establishment of the cell theory, in normal biology, was
swiftly followed by a “cellular pathology,” as its logical counterpart.
I need not remind you how great an instrument of investigation this
doctrine has proved in the hands of the man of genius to whom its
development is due, and who would probably be the last to forget that
abnormal conditions of the co-ordinative and distributive machinery of
the body are no less important factors of disease.
Henceforward, as it appears to me, the connection of medicine with the
biological sciences is clearly defined. Pure pathology is that branch
of biology which defines the particular perturbation of cell-life, or
of the co-ordinating machinery, or of both, on which the phenomena of
disease depend.
Those who are conversant with the present state of biology will hardly
hesitate to admit that the conception of the life of one of the higher
animals as the summation of the lives of a cell aggregate, brought into
harmonious action by a co-ordinative machinery formed by some of these
cells, constitutes a permanent acquisition of physiological science.
But the last form of the battle between the animistic and the physical
views of life is seen in the contention whether the physical analysis
of vital phenomena can be carried beyond this point or not.
There are some to whom living protoplasm is a substance, even such as
Harvey conceived the blood to be, “summâ cum providentiâ et intellectu
in finem certum agens, quasi ratiocinio quodam;” and who look with as
little favour as Bichat did, upon any attempt to apply the principles
and the methods of physics and chemistry to the investigation of the
vital processes of growth, metabolism, and contractility. They stand
upon the ancient ways; only, in accordance with that progress towards
democracy, which a great political writer has declared to be the fatal
characteristic of modern times, they substitute a republic formed by a
few billion of “animulæ” for the monarchy of the all-pervading “anima.”
Others, on the contrary, supported by a robust faith in the universal
applicability of the principles laid down by Descartes, and seeing
that the actions called “vital” are, so far as we have any means of
knowing, nothing but changes of place of particles of matter, look to
molecular physics to achieve the analysis of the living protoplasm
itself into a molecular mechanism. If there is any truth in the
received doctrines of physics, that contrast between living and inert
matter, on which Bichat lays so much stress, does not exist. In nature,
nothing is at rest, nothing is amorphous; the simplest particle of
that which men in their blindness are pleased to call “brute matter”
is a vast aggregate of molecular mechanisms performing complicated
movements of immense rapidity, and sensitively adjusting themselves
to every change in the surrounding world. Living matter differs from
other matter in degree and not in kind; the microcosm repeats the
macrocosm; and one chain of causation connects the nebulous original of
suns and planetary systems with the protoplasmic foundation of life and
organisation.
From this point of view, pathology is the analogue of the theory of
perturbations in astronomy; and therapeutics resolves itself into
the discovery of the means by which a system of forces competent to
eliminate any given perturbation may be introduced into the economy.
And, as pathology bases itself upon normal physiology, so therapeutics
rests upon pharmacology; which is, strictly speaking, a part of the
great biological topic of the influence of conditions on the living
organism, and has no scientific foundation apart from physiology.
It appears to me that there is no more hopeful indication of the
progress of medicine towards the ideal of Descartes than is to
be derived from a comparison of the state of pharmacology, at the
present day, with that which existed forty years ago. If we consider
the knowledge positively acquired, in this short time, of the _modus
operandi_ of urari, of atropia, of physostigmin, of veratria, of casca,
of strychnia, of bromide of potassium, of phosphorus, there can surely
be no ground for doubting that, sooner or later, the pharmacologist
will supply the physician with the means of affecting, in any desired
sense, the functions of any physiological element of the body. It will,
in short, become possible to introduce into the economy a molecular
mechanism which, like a very cunningly-contrived torpedo, shall find
its way to some particular group of living elements, and cause an
explosion among them, leaving the rest untouched.
The search for the explanation of diseased states in modified
cell-life; the discovery of the important part played by parasitic
organisms in the ætiology of disease; the elucidation of the action of
medicaments by the methods and the data of experimental physiology;
appear to me to be the greatest steps which have ever been made towards
the establishment of medicine on a scientific basis. I need hardly say
they could not have been made except for the advance of normal biology.
There can be no question, then, as to the nature or the value of the
connection between medicine and the biological sciences. There can
be no doubt that the future of pathology and of therapeutics, and,
therefore, that of practical medicine, depends upon the extent to
which those who occupy themselves with these subjects are trained in
the methods and impregnated with the fundamental truths of biology.
And, in conclusion, I venture to suggest that the collective sagacity
of this Congress could occupy itself with no more important question
than with this: How is medical education to be arranged, so that,
without entangling the student in those details of the systematist
which are valueless to him, he may be enabled to obtain a firm grasp of
the great truths respecting animal and vegetable life, without which,
notwithstanding all the progress of scientific medicine, he will still
find himself an empiric?
FOOTNOTES:
[1] See _Joseph Priestley_, p. 94, _infra_.
[2] The advocacy of the introduction of physical science into general
education by George Combe and others commenced a good deal earlier; but
the movement had acquired hardly any practical force before the time to
which I refer.
[3] _Essays in Criticism_, p. 37.
[4] “Quamvis enim melius sit bene facere quam nosse, prius tamen est
nosse quam facere.”—“Karoli Magni Regis Constitutio de Scholis per
singula Episcopia et Monasteria instituendis,” addressed to the Abbot
of Fulda. Baluzius, “Capitularia Regum Francorum,” T. i., p. 202.
[5] Inaugural Address delivered to the University of St. Andrew
February 1, 1867, by J. S. Mill, Rector of the University (pp. 32, 33).
[6] “Suggestions for Academical Organisation, with Especial Reference
to Oxford.” By the Rector of Lincoln.
[7] Goethe, _Zahme Xenien, Vierte Abtheilung_. I should be glad to take
credit for the close and vigorous English version; but it is my wife’s,
and not mine.
[8] See the “Programme” for 1878, issued by the Society of Arts, p. 14.
[9] It is perhaps advisable to remark that the important question of
the professional education of managers of industrial works is not
touched in the foregoing remarks.
[10] “Quasi cursores, vitaï lampada tradunt.”—LUCR. _De Rerum Nat._ ii.
78.
[11] “Life and Correspondence of Dr. Priestley,” by J. T. Rutt. Vol. i.
p. 50.
[12] “Autobiography,” §§ 100, 101.
[13] See “The Life of Mary Anne Schimmelpenninck.” Mrs.
Schimmelpenninck (_née_ Galton) remembered Priestley very well, and her
description of him is worth quotation:—“A man of admirable simplicity,
gentleness and kindness of heart, united with great acuteness of
intellect. I can never forget the impression produced on me by the
serene expression of his countenance. He, indeed, seemed present with
God by recollection, and with man by cheerfulness. I remember that,
in the assembly of these distinguished men, amongst whom Mr. Boulton,
by his noble manner, his fine countenance (which much resembled that
of Louis XIV.), and princely munificence, stood pre-eminently as the
great Mecænas; even as a child, I used to feel, when Dr. Priestley
entered after him, that the glory of the one was terrestrial, that of
the other celestial; and utterly far as I am removed from a belief in
the sufficiency of Dr. Priestley’s theological creed, I cannot but here
record this evidence of the eternal power of any portion of the truth
held in its vitality.”
[14] Even Mrs. Priestley, who might be forgiven for regarding the
destroyers of her household gods with some asperity, contents herself,
in writing to Mrs. Barbauld, with the sarcasm that the Birmingham
people “will scarcely find so many respectable characters, a second
time, to make a bonfire of.”
[15] “Experiments and Observations on Different Kinds of Air,” vol. ii.
p. 31.
[16] _Ibid._ pp. 34, 35.
[17] “Experiments and Observations on Different Kinds of Air,” vol. ii.
p. 40.
[18] _Ibid._ p. 48.
[19] _Ibid._ p. 55.
[20] “Experiments and Observations on Different Kinds of Air,” vol. ii.
p. 60. The italics are Priestley’s own.
[21] “In all the newspapers and most of the periodical publications
I was represented as an unbeliever in Revelation, and no better than
an atheist.”—“Autobiography,” Rutt. vol. i. p. 124. “On the walls of
houses, etc., and especially where I usually went, were to be seen, in
large characters, ‘MADAN FOR EVER; DAMN PRIESTLEY; NO PRESBYTERIANISM;
DAMN THE PRESBYTERIANS,’ etc. etc.; and, at one time, I was followed by
a number of boys, who left their play, repeating what they had seen on
the walls, and shouting out, ‘_Damn Priestley; damn him, damn him, for
ever, for ever_,’ etc. etc. This was no doubt a lesson which they had
been taught by their parents, and what they, I fear, had learned from
their superiors.”—“Appeal to the Public on the Subject of the Riots at
Birmingham.”
[22] First Series. “On Some of the Peculiarities of the Christian
Religion.” Essay I. Revelation of a Future State.