priori_ objections to the doctrine of biological evolution appear
childish. Any one who has watched the gradual formation of a
complicated animal from the protoplasmic mass, which constitutes the
essential element of a frog’s or a hen’s egg, has had under his eyes
sufficient evidence that a similar evolution of the whole animal world
from the like foundation is, at any rate, possible.
Yet another product of investigation has largely contributed to the
removal of the objections to the doctrine of evolution current in 1859.
It is the proof afforded by successive discoveries that Mr. Darwin
did not over-estimate the imperfection of the geological record. No
more striking illustration of this is needed than a comparison of our
knowledge of the mammalian fauna of the Tertiary epoch in 1859 with its
present condition. M. Gaudry’s researches on the fossils of Pikermi
were published in 1868, those of Messrs. Leidy, Marsh, and Cope, on
the fossils of the Western Territories of America, have appeared
almost wholly since 1870, those of M. Filhol on the phosphorites of
Quercy in 1878. The general effect of these investigations has been
to introduce to us a multitude of extinct animals, the existence of
which was previously hardly suspected; just as if zoologists were to
become acquainted with a country, hitherto unknown, as rich in novel
forms of life as Brazil or South Africa once were to Europeans. Indeed,
the fossil fauna of the Western Territories of America bids fair to
exceed in interest and importance all other known Tertiary deposits
put together; and yet, with the exception of the case of the American
tertiaries, these investigations have extended over very limited areas;
and, at Pikermi, were confined to an extremely small space.
Such appear to me to be the chief events in the history of the progress
of knowledge during the last twenty years, which account for the
changed feeling with which the doctrine of evolution is at present
regarded by those who have followed the advance of biological science,
in respect of those problems which bear indirectly upon that doctrine.
But all this remains mere secondary evidence. It may remove dissent,
but it does not compel assent. Primary and direct evidence in favour of
evolution can be furnished only by palæontology. The geological record,
so soon as it approaches completeness, must, when properly questioned,
yield either an affirmative or a negative answer: if evolution has
taken place, there will its mark be left; if it has not taken place,
there will lie its refutation.
What was the state of matters in 1859? Let us hear Mr. Darwin, who may
be trusted always to state the case against himself as strongly as
possible.
“On this doctrine of the extermination of an infinitude of connecting
links between the living and extinct inhabitants of the world, and at
each successive period between the extinct and still older species,
why is not every geological formation charged with such links? Why
does not every collection of fossil remains afford plain evidence
of the gradation and mutation of the forms of life? We meet with no
such evidence, and this is the most obvious and plausible of the many
objections which may be urged against my theory.”[95]
Nothing could have been more useful to the opposition than this
characteristically candid avowal, twisted as it immediately was into
an admission that the writer’s views were contradicted by the facts of
palæontology. But, in fact, Mr. Darwin made no such admission. What he
says in effect is, not that palæontological evidence is against him,
but that it is not distinctly in his favour; and, without attempting
to attenuate the fact, he accounts for it by the scantiness and the
imperfection of that evidence.
What is the state of the case now, when, as we have seen, the amount
of our knowledge respecting the mammalia of the Tertiary epoch
is increased fifty-fold, and in some directions even approaches
completeness?
Simply this, that, if the doctrine of evolution had not existed,
palæontologists must have invented it, so irresistibly is it forced
upon the mind by the study of the remains of the Tertiary mammalia
which have been brought to light since 1859.
Among the fossils of Pikermi, Gaudry found the successive stages
by which the ancient civets passed into the more modern hyænas;
through the Tertiary deposits of Western America, Marsh tracked the
successive forms by which the ancient stock of the horse has passed
into its present form; and innumerable less complete indications of
the mode of evolution of other groups of the higher mammalia have been
obtained. In the remarkable memoir on the phosphorites of Quercy, to
which I have referred, M. Filhol describes no fewer than seventeen
varieties of the genus _Cynodictis_, which fill up all the interval
between the viverine animals and the bear-like dog _Amphicyon_; nor
do I know any solid ground of objection to the supposition that, in
this _Cynodictis-Amphicyon_ group, we have the stock whence all the
Viveridæ, Felidæ, Hyænidæ, Canidæ, and perhaps the Procyonidæ and
Ursidæ, of the present fauna have been evolved. On the contrary, there
is a great deal to be said in favour.
In the course of summing up his results, M. Filhol observes:—
“During the epoch of the phosphorites, great changes took
place in animal forms, and almost the same types as those
which now exist became defined from one another.
“Under the influence of natural conditions of which
we have no exact knowledge, though traces of them are
discoverable, species have been modified in a thousand
ways: races have arisen which, becoming fixed, have thus
produced a corresponding number of secondary species.”
In 1859, language of which this is an unintentional paraphrase,
occurring in the “Origin of Species,” was scouted as wild speculation;
at present, it is a sober statement of the conclusions to which an
acute and critically-minded investigator is led by large and patient
study of the facts of palæontology. I venture to repeat what I have
said before, that, so far as the animal world is concerned, evolution
is no longer a speculation, but a statement of historical fact. It
takes its place alongside of those accepted truths which must be
reckoned with by philosophers of all schools.
Thus when, on the first day of October next, the “Origin of Species”
comes of age, the promise of its youth will be amply fulfilled; and we
shall be prepared to congratulate the venerated author of the book, not
only that the greatness of his achievement and its enduring influence
upon the progress of knowledge have won him a place beside our Harvey;
but, still more, that, like Harvey, he has lived long enough to outlast
detraction and opposition, and to see the stone that the builders
rejected become the head-stone of the corner.
XIII.
THE CONNECTION OF THE BIOLOGICAL SCIENCES WITH MEDICINE.
The great body of theoretical and practical knowledge which has been
accumulated by the labours of some eighty generations, since the dawn
of scientific thought in Europe, has no collective English name to
which an objection may not be raised; and I use the term “medicine” as
that which is least likely to be misunderstood; though, as every one
knows, the name is commonly applied, in a narrower sense, to one of the
chief divisions of the totality of medical science.
Taken in this broad sense, “medicine” not merely denotes a kind
of knowledge, but it comprehends the various applications of that
knowledge to the alleviation of the sufferings, the repair of the
injuries, and the conservation of the health, of living beings. In
fact, the practical aspect of medicine so far dominates over every
other, that the “Healing Art” is one of its most widely-received
synonyms. It is so difficult to think of medicine otherwise than as
something which is necessarily connected with curative treatment, that
we are apt to forget that there must be, and is, such a thing as a
pure science of medicine—a “pathology” which has no more necessary
subservience to practical ends than has zoology or botany.
The logical connection between this purely scientific doctrine of
disease, or pathology, and ordinary biology, is easily traced.
Living matter is characterised by its innate tendency to exhibit a
definite series of the morphological and physiological phenomena which
constitute organisation and life. Given a certain range of conditions,
and these phenomena remain the same, within narrow limits, for each
kind of living thing. They furnish the normal and typical character
of the species, and, as such, they are the subject-matter of ordinary
biology.
Outside the range of these conditions, the normal course of the
cycle of vital phenomena is disturbed; abnormal structure makes its
appearance, or the proper character and mutual adjustment of the
functions cease to be preserved. The extent and the importance of these
deviations from the typical life may vary indefinitely. They may have
no noticeable influence on the general well-being of the economy, or
they may favour it. On the other hand, they may be of such a nature
as to impede the activities of the organism, or even to involve its
destruction.
In the first case, these perturbations are ranged under the wide and
somewhat vague category of “variations;” in the second, they are called
lesions, states of poisoning, or diseases; and, as morbid states, they
lie within the province of pathology. No sharp line of demarcation can
be drawn between the two classes of phenomena. No one can say where
anatomical variations end and tumours begin, nor where modification
of function, which may at first promote health, passes into disease.
All that can be said is, that whatever change of structure or function
is hurtful belongs to pathology. Hence it is obvious that pathology
is a branch of biology; it is the morphology, the physiology, the
distribution, the ætiology of abnormal life.
However obvious this conclusion may be now, it was nowise apparent
in the infancy of medicine. For it is a peculiarity of the physical
sciences, that they are independent in proportion as they are
imperfect; and it is only as they advance that the bonds which really
unite them all become apparent. Astronomy had no manifest connection
with terrestrial physics before the publication of the “Principia;”
that of chemistry with physics is of still more modern revelation;
that of physics and chemistry with physiology, has been stoutly denied
within the recollection of most of us, and perhaps still may be.
Or, to take a case which affords a closer parallel with that of
medicine. Agriculture has been cultivated from the earliest times,
and, from a remote antiquity, men have attained considerable practical
skill in the cultivation of the useful plants, and have empirically
established many scientific truths concerning the conditions under
which they flourish. But, it is within the memory of many of us, that
chemistry on the one hand, and vegetable physiology on the other,
attained a stage of development such that they were able to furnish
a sound basis for scientific agriculture. Similarly, medicine took
its rise in the practical needs of mankind. At first, studied without
reference to any other branch of knowledge, it long maintained, indeed
still to some extent maintains, that independence. Historically, its
connection with the biological sciences has been slowly established,
and the full extent and intimacy of that connection are only now
beginning to be apparent. I trust I have not been mistaken in supposing
that an attempt to give a brief sketch of the steps by which a
philosophical necessity has become an historical reality, may not be
devoid of interest, possibly of instruction, to the members of this
great Congress, profoundly interested as all are in the scientific
development of medicine.
The history of medicine is more complete and fuller than that of any
other science, except, perhaps, astronomy; and, if we follow back the
long record as far as clear evidence lights us, we find ourselves taken
to the early stages of the civilisation of Greece. The oldest hospitals
were the temples of Æsculapius; to these Asclepeia, always erected on
healthy sites, hard by fresh springs and surrounded by shady groves,
the sick and the maimed resorted to seek the aid of the god of health.
Votive tablets or inscriptions recorded the symptoms, no less than the
gratitude, of those who were healed; and, from these primitive clinical
records, the half-priestly, half-philosophic caste of the Asclepiads
compiled the data upon which the earliest generalisations of medicine,
as an inductive science, were based.
In this state, pathology, like all the inductive sciences at their
origin, was merely natural history; it registered the phenomena of
disease, classified them, and ventured upon a prognosis, wherever
the observation of constant co-existences and sequences suggested a
rational expectation of the like recurrence under similar circumstances.
Further than this it hardly went. In fact, in the then state of
knowledge, and in the condition of philosophical speculation at that
time, neither the causes of the morbid state, nor the _rationale_ of
treatment, were likely to be sought for as we seek for them now. The
anger of a god was a sufficient reason for the existence of a malady,
and a dream ample warranty for therapeutic measures; that a physical
phenomenon must needs have a physical cause was not the implied or
expressed axiom that it is to us moderns.
The great man whose name is inseparately connected with the foundation
of medicine, Hippocrates, certainly knew very little, indeed
practically nothing, of anatomy or physiology; and he would, probably,
have been perplexed, even to imagine the possibility of a connection
between the zoological studies of his contemporary Democritus and
medicine. Nevertheless, in so far as he, and those who worked before
and after him, in the same spirit, ascertained, as matters of
experience, that a wound, or a luxation, or a fever, presented such
and such symptoms, and that the return of the patient to health was
facilitated by such and such measures, they established laws of
nature, and began the construction of the science of pathology. All
true science begins with empiricism—though all true science is such
exactly, in so far as it strives to pass out of the empirical stage
into that of the deduction of empirical from more general truths.
Thus, it is not wonderful, that the early physicians had little or
nothing to do with the development of biological science; and, on the
other hand, that the early biologists did not much concern themselves
with medicine. There is nothing to show that the Asclepiads took any
prominent share in the work of founding anatomy, physiology, zoology,
and botany. Rather do these seem to have sprung from the early
philosophers, who were essentially natural philosophers, animated by
the characteristically Greek thirst for knowledge as such. Pythagoras,
Alcmeon, Democritus, Diogenes of Apollonia, are all credited with
anatomical and physiological investigations; and, though Aristotle is
said to have belonged to an Asclepiad family, and not improbably owed
his taste for anatomical and zoological inquiries to the teachings of
his father, the physician Nicomachus, the “Historia Animalium,” and
the treatise “De Partibus Animalium,” are as free from any allusion to
medicine as if they had issued from a modern biological laboratory.
It may be added, that it is not easy to see in what way it could have
benefited a physician of Alexander’s time to know all that Aristotle
knew on these subjects. His human anatomy was too rough to avail
much in diagnosis; his physiology was too erroneous to supply data
for pathological reasoning. But when the Alexandrian school, with
Erasistratus and Herophilus at their head, turned to account the
opportunities of studying human structure, afforded to them by the
Ptolemies, the value of the large amount of accurate knowledge thus
obtained to the surgeon for his operations, and to the physician for
his diagnosis of internal disorders, became obvious, and a connection
was established between anatomy and medicine, which has ever become
closer and closer. Since the revival of learning, surgery, medical
diagnosis, and anatomy have gone hand in hand. Morgagni called his
great work, “De sedibus et causis morborum per anatomen indagatis,” and
not only showed the way to search out the localities and the causes
of disease by anatomy, but himself travelled wonderfully far upon the
road. Bichat, discriminating the grosser constituents of the organs and
parts of the body, one from another, pointed out the direction which
modern research must take; until, at length, histology, a science of
yesterday, as it seems to many of us, has carried the work of Morgagni
as far as the microscope can take us, and has extended the realm of
pathological anatomy to the limits of the invisible world.
Thanks to the intimate alliance of morphology with medicine, the
natural history of disease has, at the present day, attained a
high degree of perfection. Accurate regional anatomy has rendered
practicable the exploration of the most hidden parts of the organism,
and the determination, during life, of morbid changes in them;
anatomical and histological postmortem investigations have supplied
physicians with a clear basis upon which to rest the classification
of diseases, and with unerring tests of the accuracy or inaccuracy of
their diagnoses.
If men could be satisfied with pure knowledge, the extreme precision
with which, in these days, a sufferer may be told what is happening,
and what is likely to happen, even in the most recondite parts of
his bodily frame, should be as satisfactory to the patient as it is
to the scientific pathologist who gives him the information. But I
am afraid it is not; and even the practising physician, while nowise
underestimating the regulative value of accurate diagnosis, must often
lament that so much of his knowledge rather prevents him from doing
wrong than helps him to do right.
A scorner of physic once said that nature and disease may be compared
to two men fighting, the doctor to a blind man with a club, who strikes
into the _melée_, sometimes hitting the disease, and sometimes hitting
nature. The matter is not mended if you suppose the blind man’s hearing
to be so acute that he can register every stage of the struggle, and
pretty clearly predict how it will end. He had better not meddle at
all, until his eyes are opened—until he can see the exact position of
the antagonists, and make sure of the effect of his blows. But that
which it behoves the physician to see, not, indeed, with his bodily
eye, but with clear, intellectual vision, is a process, and the chain
of causation involved in that process. Disease, as we have seen, is
a perturbation of the normal activities of a living body, and it is,
and must remain, unintelligible, so long as we are ignorant of the
nature of these normal activities. In other words, there could be no
real science of pathology until the science of physiology had reached a
degree of perfection unattained, and indeed unattainable, until quite
recent times.
So far as medicine is concerned, I am not sure that physiology, such
as it was down to the time of Harvey, might as well not have existed.
Nay, it is perhaps no exaggeration to say that, within the memory of
living men, justly renowned practitioners of medicine and surgery knew
less physiology than is now to be learned from the most elementary
text-book; and, beyond a few broad facts, regarded what they did know
as of extremely little practical importance. Nor am I disposed to
blame them for this conclusion; physiology must be useless, or worse
than useless, to pathology, so long as its fundamental conceptions are
erroneous.
Harvey is often said to be the founder of modern physiology; and there
can be no question that the elucidations of the function of the heart,
of the nature of the pulse, and of the course of the blood, put forth
in the ever-memorable little essay, “De motu cordis,” directly worked
a revolution in men’s views of the nature and of the concatenation of
some of the most important physiological processes among the higher
animals; while, indirectly, their influence was perhaps even more
remarkable.
But, though Harvey made this signal and perennially important
contribution to the physiology of the moderns, his general conception
of vital processes was essentially identical with that of the ancients;
and, in the “Exercitationes de generatione,” and notably in the
singular chapter “De calido innato,” he shows himself a true son of
Galen and of Aristotle.
For Harvey, the blood possesses powers superior to those of the
elements; it is the seat of a soul which is not only vegetative, but
also sensitive and motor. The blood maintains and fashions all parts of
the body, “idque summâ cum providentiâ et intellectu in finem certum
agens, quasi ratiocinio quodam uteretur.”
Here is the doctrine of the “pneuma,” the product of the philosophical
mould into which the animism of primitive men ran in Greece, in full
force. Nor did its strength abate for long after Harvey’s time. The
same ingrained tendency of the human mind to suppose that a process
is explained when it is ascribed to a power of which nothing is known
except that it is the hypothetical agent of the process, gave rise, in
the next century, to the animism of Stahl; and, later, to the doctrine
of a vital principle, that “asylum ignorantiæ” of physiologists, which
has so easily accounted for everything and explained nothing, down to
our own times.
Now the essence of modern, as contrasted with ancient, physiological
science appears to me to lie in its antagonism to animistic hypotheses
and animistic phraseology. It offers physical explanations of vital
phenomena, or frankly confesses that it has none to offer. And, so far
as I know, the first person who gave expression to this modern view
of physiology, who was bold enough to enunciate the proposition that
vital phenomena, like all the other phenomena of the physical world,
are, in ultimate analysis, resolvable into matter and motion, was René
Descartes.
The fifty-four years of life of this most original and powerful thinker
are widely overlapped, on both sides, by the eighty of Harvey, who
survived his younger contemporary by seven years, and takes pleasure
in acknowledging the French philosopher’s appreciation of his great
discovery.
In fact, Descartes accepted the doctrine of the circulation as
propounded by “Harvæus médecin d’Angleterre,” and gave a full account
of it in his first work, the famous “Discours de la Méthode,” which
was published in 1637, only nine years after the exercitation “De motu
cordis;” and, though differing from Harvey on some important points
(in which it may be noted, in passing, Descartes was wrong and Harvey
right), he always speaks of him with great respect. And so important
does the subject seem to Descartes, that he returns to it in the
“Traité des Passions,” and in the “Traité de l’Homme.”