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[Illustration: KARL ERNST von BAER (in old age), from the
picture by Hagen-Schwarz.
(_By permission of the Berlin Photographic Company, 133 New Bond
Street, London, W._)]
HISTORY OF
BIOLOGY
BY
L. C. MIALL, D.Sc., F.R.S.,
FORMERLY PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF LEEDS
[ISSUED FOR THE RATIONALIST PRESS ASSOCIATION, LIMITED]
London:
WATTS & CO.,
17 JOHNSON'S COURT, FLEET STREET, E.C.
1911
CONTENTS
PAGE
Introduction 1
Biology of the ancients. Extinction of scientific
inquiry. Revival of knowledge.
PERIOD I (1530-1660) 7
Characteristics of the period. The revival of
botany. The revival of zoology. Early notions of
system. The first English naturalists. The rise of
experimental physiology. The natural history of
distant lands (sixteenth century and earlier). Agriculture,
horticulture, and silk-culture in the sixteenth
century.
PERIOD II (1661-1740) 28
Characteristics of the period. The minute anatomists.
Early notions about the nature of fossils. Comparative
anatomy; the study of biological types. Adaptations
of plants and animals; natural theology.
Spontaneous generation. The natural history of
John Ray. The scale of nature. The sexes of
flowering plants.
PERIOD III (1741-1789) 49
Characteristics of the period. Systems of flowering
plants; Linnæus and the Jussieus. Réaumur and
the _History of Insects_. The budding-out of new
animals (Hydra); another form of propagation without
mating (aphids). The historical or comparative
method; Montesquieu and Buffon. Amateur students
of living animals. Intelligence and instinct in the
lower animals. The food of green plants. The
metamorphoses of plants. Early notions about the
lower plants.
PERIOD IV (1790-1858) 89
Characteristics of the period. Sprengel and the
fertilisation of flowers. Cuvier and the rise of
palæontology. Chamisso on the alternation of
generations in Salpa. Baer and the development of
animals. The cell-theory. The scientific investigation
of the higher cryptogams. The enrichment of
English gardens. Humboldt as a traveller and a
biologist. Premonitions of a biological theory of
evolution.
PERIOD V (1859 and Later) 124
Darwin on the _Origin of Species_. Pasteur's experimental
study of microbes.
Chronological Table 141
The Sub-Divisions of Biology 146
Bibliography 147
Index 149
LIST OF ILLUSTRATIONS
PAGE
Karl Ernst von Baer _Frontispiece_
Figure from Fuchs' "Historia Stirpium" 8
Leonhard Fuchs 10
Comparative Figures of Skeletons of Man and
Bird, from Belon's Book of Birds 14, 15
Marcello Malpighi 31
Antony van Leeuwenhoek 33
John Ray 42
Carolus Linnæus 53
Georges Louis Leclerc, Comte de Buffon 65
Georges Cuvier 99
INTRODUCTION
Four hundred years ago, say in the year 1500, Biology, the science
of life, was represented chiefly by a slight and inaccurate natural
history of plants and animals. Botany attracted more students than any
other branch, because it was recognised as a necessary aid to medical
practice. The zoology of the time, extracted from ancient books, was
most valued as a source from which preachers and moralists might draw
impressive emblems. Anatomy and physiology were taught out of Galen to
the more learned of physicians and surgeons. Some meagre notices of the
plants and animals of foreign countries, mingled with many childish
fables, eked out the scanty treatises of European natural history. It
was not yet generally admitted that fossil bones, teeth, and shells
were the remains of extinct animals.
It is the purpose of the following chapters to show how this
insignificant body of information expanded into the biology of the
twentieth century; how it became enriched by a multitude of new facts,
strengthened by new methods and animated by new ideas.
The Biology of the Ancients.
Long before the year 1500 there had been a short-lived science of
biology, and it is necessary to explain how it arose and how it became
quenched. Ancient books and the languages in which they are written
teach us that in very remote times men attended to the uses of
plants and the habits of animals, gave names to familiar species, and
recognised that while human life has much in common with the life of
animals, it has something in common with the life of plants. Abundant
traces of an interest in living things are to be found in the oldest
records of India, Palestine, and Egypt. Still more interesting, at
least to the inhabitants of Western Europe, is the biology of the
ancient Greeks. The Greeks were an open-air people, dwelling in a
singularly varied country nowhere far removed from the mountains or the
sea. Intellectually they were distinguished by curiosity, imagination,
and a strong taste for reasoning. Hence it is not to be wondered at
that natural knowledge should have been widely diffused among them,
nor that some of them should have excelled in science. Besides all the
rest, the Greeks were a literary people, who have left behind them a
copious record of their thoughts and experience. Greek science, and
Greek biology in particular, are therefore of peculiar interest and
value.
Greek naturalists in or before the age of Alexander the Great had
collected and methodised the lore of the farmer, gardener, hunter,
fisherman, herb-gatherer, and physician; the extant writings of
Aristotle and Theophrastus give us some notion of what had been
discovered down to that time.
Aristotle shows a wide knowledge of animals. He dwells upon peculiar
instincts, such as the migration of birds, the nest-building of the
fish Phycis, the capture of prey by the fish Lophius, the protective
discharge of ink by Sepia, and the economy of the hive-bee. He is fond
of combining many particular facts into general statements like these:
No animal which has wings is without legs; animals with paired horns
have cloven feet and a complex, ruminating stomach, and lack the
upper incisor teeth; hollow horns, supported by bony horn-cores, are
not shed, but solid horns are shed every year; birds which are armed
with spurs are never armed with lacerating claws; insects which bear a
sting in the head are always two-winged, but insects which bear their
sting behind are four-winged. He traces analogies between things which
are superficially unlike, such as plants and animals—the mouth of the
animal and the root of the plant. The systematic naturalist is prone to
attend chiefly to the differences between species; Aristotle is equally
interested in their resemblances. The systematic naturalist arranges
his descriptions under species, Aristotle under organs or functions; he
is the first of the comparative anatomists. His conception of biology
(the word but not the thing is modern) embraces both animals and
plants, anatomy, physiology, and system. That he possessed a zoological
system whose primary divisions were nearly as good as those of Linnæus
is clear from the names and distinctions which he employs; but no
formal system is set forth in his extant writings. His treatise on
plants has unfortunately been lost.
Aristotle, like all the Greeks, was unpractised in experiment. It had
not yet been discovered that an experiment may quickly and certainly
decide questions which might be argued at great length without result,
nor that an experiment devised to answer one question may suggest
others possibly more important than the first. Deliberate scientific
experiments are so rare among the Greeks that we can hardly point to
more than two—those on refraction of light, commonly attributed to
Ptolemy, and those by which Pythagoras is supposed to have ascertained
the numerical relations of the musical scale. Aristotle was the last
great man of science who lived and taught in Greece. His writings
disappeared from view for many centuries, and when they were recovered
they were not so much examined and corrected as idolised.
Greece lost her liberty at Chaeronea, and with liberty her fairest
hopes of continued intellectual development. Nevertheless, during
a great part of a thousand years the Greek and Semitic school of
Alexandria cultivated the sciences with diligence and success. We must
say nothing here about the geometry, astronomy, optics, or geography
there taught, but merely note that Herophilus and Erasistratus,
unimpeded by that repugnance to mutilation of the human body which had
been insurmountable at Athens, made notable advances in anatomy and
physiology. From this time a fair knowledge of the bodily structure of
man, decidedly superior to that which Aristotle had possessed, was at
the command of every educated biologist.
The genius of Rome applied itself to purposes remote from science. The
example of Alexandria had its influence, however, upon some inhabitants
of the Roman Empire. Galen of Pergamum in Asia Minor prosecuted the
study of human anatomy. His knowledge of the parts which can be
investigated by simple dissection was extensive, but he was unpractised
in experimental physiology. Hence his teaching, though full with
respect to the skeleton, the chief viscera, and the parts of the brain,
was faulty with respect to the flow of the blood through the heart and
body. Ages after his death the immense reputation of Galen, like that
of Aristotle, was used with great effect to discredit more searching
inquiries. Under the Roman Empire also flourished Dioscorides, who
wrote on the plants used in medicine, and the elder Pliny, who
compiled a vast, but wholly uncritical, encyclopædia of natural history.
We see from these facts how ancient nations, inhabiting the
Mediterranean basin and largely guided by Greek intelligence, had
not only striven to systematise that knowledge of plants and animals
which every energetic and observant race is sure to possess, but
had with still more determination laboured to create a science of
human anatomy which should be serviceable to the art of medicine.
The effort was renewed time after time during five or six centuries,
but was at last crushed under the conquests of a long succession of
foreign powers—Macedonians, Romans, Mohammedan Arabs, and northern
barbarians—each more hostile to knowledge than its predecessors.
Extinction of Scientific Inquiry.
The decline and fall of the Roman Empire brought with it the temporary
extinction of civilisation in a great part of Western Europe. Science
was during some centuries taught, if taught at all, out of little
manuals compiled from ancient authors. Geometry and astronomy were
supplanted by astrology and magic; medicine was rarely practised except
by Jews and the inmates of religious houses. Literature and the fine
arts died out almost everywhere.
No doubt the practical knowledge of the farmer and gardener, as well
as the lore of the country-side, was handed down from father to son
during all the ages of darkness, but the natural knowledge transmitted
by books suffered almost complete decay. The teaching ascribed to
Physiologus is a sufficient proof of this statement. Physiologus
is the name given in many languages during a thousand years to the
reputed author of popular treatises of zoology, which are also called
Bestiaries, or books of beasts. Here it was told how the lion sleeps
with open eyes, how the crocodile weeps when it has eaten a man, how
the elephant has but one joint in its leg and cannot lie down, how the
pelican brings her young back to life by sprinkling them with her own
blood. The emblems of the Bestiaries supplied ornaments to mediæval
sermons; as late as Shakespeare's day poetry drew from them no small
part of her imagery; they were carved on the benches, stalls, porches,
and gargoyles of the churches.
In the last years of the tenth century A.D. faint signs of revival
appeared, which became distinct in another hundred years. From that day
to our own the progress has been continuous.
Revival of Knowledge.
By the thirteenth century the rate of progress had become rapid. To
this age are ascribed the introduction of the mariner's compass,
gunpowder, reading glasses, the Arabic numerals, and decimal
arithmetic. In the fourteenth century trade with the East revived;
Central Asia and even the Far East were visited by Europeans;
universities were multiplied; the revival of learning, painting, and
sculpture was accomplished in Italy. Engraving on wood or copper
and printing from moveable types date from the fifteenth century.
The last decade of this century is often regarded as the close of
the Middle Ages; it really marks, not the beginning, but only an
extraordinary acceleration, of the new progressive movement, which
set in long before. To the years between 1490 and 1550 belong the
great geographical discoveries of the Spaniards in the West and of the
Portuguese in the East, as well as the Reformation and the revival of
science.
PERIOD I.
1530-1660
Characteristics of the Period.
This is the time of the revival of science; the revival of learning
had set in about two centuries earlier. Europe was now repeatedly
devastated by religious wars (the revolt of the Netherlands, the wars
of the League in France, the Thirty Years' war, the civil war in
England). Learning was still mainly classical and scholastic; nearly
every writer whom we shall have occasion to name had been educated at a
university, and was able to read and write Latin. Two great extensions
of knowledge helped to widen the thoughts of men. It became known for
the first time that our planet is an insignificant member of a great
solar system, and that Christendom is both in extent and population but
a small fraction of the habitable globe.
The Revival of Botany.
Botany was among the first of the sciences to revive. Its comparatively
early start was due to close association with the lucrative profession
of medicine. Medicine itself was slow to shake off the unscientific
tradition of the Middle Ages, and its backwardness favoured, as
it happened, the progress of botany. In the sixteenth century the
physician was above all things the prescriber of drugs, and since
nine-tenths of the drugs were got from plants, botanical knowledge was
reckoned as one of his chief qualifications. All physicians professed
to be botanists, and every botanist was thought fit to practise
medicine.
[Illustration:
POLYGONATVM
LATIFOLIVM
FIGURE OF SOLOMON'S SEAL.
From Fuchs' _Historia Stirpium_, 1542. The original occupies a folio
page.]
Three Germans, who were at once botanists and physicians—Brunfels,
Bock, and Fuchs—led the way by publishing herbals, in which the plants
of Germany were described and figured from nature. Their first editions
appeared in the years 1530, 1539, and 1542. Illustrated herbals were
then no novelty, but whereas they had hitherto supplied figures which
had been copied time after time until they had often ceased to be
recognisable, Brunfels set a pattern of better things by producing what
he called "herbarum vivæ eicones," life-like figures of the plants.
Each of the three new herbals contained hundreds of large woodcuts.
Those engraved for Fuchs are probably of higher artistic quality than
any that have appeared since. Each plant, drawn in clear outline
without shading, fills a folio page, upon which the text is not allowed
to encroach. The botanist will, however, remark that enlarged figures
are hardly ever given, so that minute flowers show as mere dots, and
that the details of the foliage are not so scrupulously delineated
as in modern figures. The text of Brunfels and Fuchs is of little
interest, being largely occupied with traditional pharmacy. Bock,
whose figures are inferior to those of Brunfels and Fuchs, makes up
for this deficiency by his graphic and sometimes amusing descriptions.
He delights in natural contrivances, such as the hooks on the twining
stem of the hop, or the elastic membrane which throws out the seeds of
wood-sorrel. Brunfels has no intelligible sequence of species; Fuchs
abandons the attempt to discover a natural succession, and adopts the
alphabetical order; Bock aims at bringing together plants which show
mutual affinity ("Gewächs einander verwandt"), though such natural
groups as he recognises are neither named nor named nor defined.
[Illustration: LEONHARD FUCHS
From his _Historia Stirpium_, 1742.]
These three German herbals really deserve to be called scientific. To
figure the plants of Germany from the life, to exclude such as existed
only in books, and to strive after a natural grouping, was a first
step towards a fruitful knowledge of plant-life. It is worth while to
dwell for a moment upon the place where these herbals were produced.
Along the Rhine civilisation and industry had for many years flourished
together. Here and in the country to the east of the great river had
sprung up that powerful union of seventy cities known in the thirteenth
century as the Confederation of the Rhine; four universities, three of
them on the banks of the Rhine, had been founded; here printing and
wood-engraving had established themselves in their infancy; here, too,
the Reformation found many early supporters. There were historical,
economic, and moral reasons why the first printed books on natural
history, illustrated by woodcuts drawn from the life, should have been
produced in the Rhineland, and why all their authors should have been
Protestants. Nearly every sixteenth-century botanist held the same
faith.
The success of the first German herbalists brought a crowd of
botanists into the field, among whom were several whose names are
still remembered with honour. Gesner of Zurich made elaborate studies
for a great history of plants, which he did not live to complete.
It was he who first pointed out that the flower and fruit give the
best indications of the natural relationships of plants, and his
many beautiful enlarged drawings set an example which has done much
for scientific botany. Botanists began to understand what natural
grouping means, and to recognise that truly natural groups are not
to be invented, but discovered. The almost accidental succession
adopted by Brunfels, the alphabetical succession of Fuchs, the division
according to uses (kitchen-herbs, coronary or garland-flowers, etc.),
and the logical, but too formal, method of Cesalpini, in which, as
in modern classification, much use was made of the divisions in the
ovary—all these were left behind. L'Obel separated, unconsciously
and imperfectly, the Monocotyledons from the Dicotyledons, recognised
several easily distinguished families of flowering plants (grasses,
umbellifers, labiates, etc.), and framed the first synoptic tables of
genera.
The Revival of Zoology.
While the physicians of the Rhineland were describing and figuring
their native plants, the study of animals began to revive. Two
very different methods of work were tried by the zoologists of the
sixteenth century. One set of men, who may be called the Encyclopædic
Naturalists, were convinced that books, and especially the books of
the ancients, constituted the chief source of information concerning
animals and most other things. They extracted whatever they could from
Aristotle, Ælian, and Pliny, adding all that was to be learned from the
narratives of recent travellers, or from the collectors of skins and
shells. The books on which they chiefly depended, being for the most
part written by men who had not grappled with practical natural history
and its problems, were unfortunately altogether inadequate. Many of
the statements brought together by the encyclopædic naturalists were
ill-attested; some were even ridiculously improbable. If inferences
from the facts were attempted—and this was rare—they were more
often propositions of morality or natural theology than the pregnant
thoughts which suggest new inquiries. Hence the encyclopædic plan,
even when pursued by men of knowledge and capacity, such as Gesner and
Aldrovandi, yielded no results proportional to the labour bestowed upon
it; the true path of biological progress had been missed. Naturalists
of another school described and figured the animals of their own
country, or at least animals which they had closely studied. Rondelet
described from personal observation the fishes of the Mediterranean;
Belon described the fishes and birds that he had met with in France and
the Levant. His _Book of Birds_ (1555) is a folio volume in which some
two hundred species are described and figured. The "naturel" (natural
history of the species) contains many curious observations. Perhaps the
best things in the book are two figures placed opposite one another and
lettered in correspondence; one shows the skeleton of a bird, the other
that of a man. The example of Rondelet and Belon was followed by other
zoological monographers, who did more for zoology than all the learning
of the encyclopædists.
Early Notions of System.
Simple-minded people, who do not feel the need of precision in matters
of natural history, have in all ages divided animals into four-footed
beasts which walk on the earth, birds which fly, fishes which swim,
and perhaps reptiles which creep. This is the classification found in
the Babylonian and Hebrew narratives of the great flood. Plants they
naturally divide into trees and herbs. It was not very long, however,
before close observers became discontented with so simple a grouping.
They discovered that the bat is no bird, though it flies; that the
whale is no fish, though it swims; that the snake comes nearer in
all essentials to the four-footed lizard, and even to the beast of
the field, than to the creeping earthworm. At a much later time they
discovered that pod-bearing or rose-like herbs may resemble pod-bearing
or rose-like trees more closely than all trees resemble each other.
Moreover, a multitude of animals became known which cannot be classed
as either beasts, birds, fishes, or reptiles, and a multitude of plants
which cannot be classed as either trees or herbs.
[Illustration: BIRD'S SKELETON.
For comparison with human skeleton (opposite), lettered to show the
answerable bones. From Belon's _Book of Birds_, 1555.]
[Illustration: HUMAN SKELETON.
For comparison with bird's skeleton (opposite), lettered to show the
answerable bones. From Belon's _Book of Birds_, 1555.]
Aristotle found himself obliged to rectify the traditional
classification of animals in order to remove gross anomalies. When
learning decayed the traditional classification came back. Thus the
_Ortus Sanitatis_ (first published in 1475, and often reprinted)
adopts the division into (1) animals and things which creep on the earth;
(2) birds and things which fly; (3) fishes and things which swim. No
consistent primary division of plants was proposed by Greek or Roman,
nor by anyone else until the seventeenth century A.D.
This conflict of systems should have raised questions concerning the
nature of classification and the relative value of characters. Some
of the most striking resemblances found among animals and plants are
only superficial; others, though far less obvious, are fundamental.
Whence this difference? Why should scientific zoology make so little of
the place of abode and the mode of locomotion; so much of the mode of
reproduction and the nature of the skeleton? The answers were vague,
and even the questions were rare and indistinct. But a metaphorical
term came into use which was henceforth more and more definitely
associated with fundamental, as distinguished from adaptive, likeness.
Such likeness was called _affinity_,[1] though no attempt was made
to explain in what sense the term was to be understood. As late as the
year 1835 one of the first botanists in Europe (Elias Fries) could
say no more about affinity between species than that it was _quoddam
supernaturale_, a supernatural property.
A tolerable outline of a classification of animals was attained much
earlier than a tolerable classification of plants. The characters
available for the classification of plants are, to begin with,
less obvious than those which the zoologist can employ. Moreover,
the botanists were restricted to a narrower view of their subject.
Zoologists, though they were expected to bestow the best part of their
time upon vertebrates, were encouraged to study all animals more
or less. Botanists, on the other hand, were practically obliged to
concentrate their attention upon the classification of the flowering
plants. The physician, herb-collector, and gardener cared nothing
about any plants except such as bear flowers and fruit; but of these
they expected full descriptions, and were clamorous for a system which
would enable even a tyro to make out every species with certainty
and ease. The task set before the botanist was comparable in respect
of difficulty with the construction of a detailed and completely
satisfactory classification of birds, which zoology has never yet been
able to produce, while for the sake of this long-unattainable object
almost everything else in botany was neglected.
The First English Naturalists.
During the greater part of three centuries (1300 to 1600), while the
revival of learning and science was proceeding actively in Italy,
France, Switzerland, and the Rhineland, England lagged behind. Humanist
studies were indeed pursued with eminent success in the England of Sir
Thomas More, but there was little else for national pride to dwell
upon. The re-opening of ancient literature, the outpouring of printed
books, the Reformation, the new mathematics and astronomy, the new
botany and zoology, were mainly the work of foreigners. Before the
seventeenth century no Englishman was recognised as the founder of a
scientific school.
Passing over Edward Wotton (1492-1555), who recast the zoology of
Aristotle with very little effect upon the progress of biology, we may
head the list of English naturalists with the name of William Turner
(_d._ 1568), who wrote on the plants and birds of Britain. Turner
was a Reformed preacher, who had been the college friend of Ridley and
Latimer. Being banished for preaching without licence, he studied
medicine and botany in Italy, at Basle and at Cologne. Under Edward
VI. he returned to England and was made Dean of Wells, fled again to
the Continent on Mary's accession, was re-instated by Elizabeth, was
suspended for non-conformity, and died not long after. Turner's herbal
(1551-63) cannot be said to have done much for English botany. The
arrangement is alphabetical, the properties and virtues of the plants
are described out of ancient authors, and most of the figures are
borrowed. Still, it was something to have the common plants of England
examined by a man who had studied under Luke Ghini, had botanised along
the Rhine, and was the pupil, friend, and correspondent of Conrad
Gesner, the most learned naturalist in Europe. Turner's _History_
_of Birds_ (_Historia Avium_) was published in Latin at Cologne
in 1544,[2] and is therefore earlier than Belon's book of birds. The
history contains here and there among passages culled from the ancients
a sprightly description of the feeding or nest-building of some
English bird, and furnishes evidence of the breeding in our islands of
birds which, like the crane, have long been known to us only as rare
visitants. Of the kite Turner says that in the cities of England it
used to snatch the meat out of the hands of children. In his day the
osprey was better known to Englishmen than they liked, for it emptied
their fishponds; anglers used to mix their bait with its fat. Turner
shows not a little of that spirit of close observation which in a later
and more tranquil age shone forth in Gilbert White.
Dr. John Caius (the name is supposed to be a Latinised form of Kay),
the second founder of a great Cambridge college, was physician in
succession to Edward VI., Mary, and Elizabeth; in his youth he had
studied under Vesalius at Padua. Like Turner he was a friend and
correspondent of Gesner, for whom he wrote an account of the dogs of
Britain (_De Canibus Britannicis_, printed in Latin in 1570), which
attempts to classify all the breeds, and to give some account of the
uses to which each was put. The list contains no bull-dog, pointer,
or modern retriever. There is a water-spaniel, however, and dogs had
already been trained to retrieve game. The turnspit, which was not a
distinct breed (Caius calls it a mongrel), has long been superseded.
Curious antiquarian information, such as mention of the weapons
formerly used by sportsmen, and obsolete names of dogs, reward the
reader of this short tract.
Thomas Moufet wrote (for Gesner again) a book on insects, which
incorporated the notes of Penny and Wotton. None of the three lived to
see the printed book, which was at last put forth by Sir Thomas Mayerne
in 1634. It is uncritical, confused, and illustrated by the rudest
possible woodcuts.
John Gerarde's _Herbal_ (1597) and Parkinson's two books of plants
are more amusing than valuable. Both authors were guilty of unscrupulous
plagiarism, a vice which cannot be atoned for by curious figures and
bits of folk-lore, nor even by command of Shakespearean English. Thomas
Johnson's edition of Gerarde (1633) is a far better book than the
original; Ray called it "Gerarde emaculatus"—_i.e._, freed from
its stains.
The succession of influential English naturalists may be said to begin
with Ray, Willughby, and Martin Lister, all of whom belong to the last
half of the seventeenth century.
The Rise of Experimental Physiology.
1543 is a memorable year in the history of science. Then appeared the
treatise of Copernicus on the _Revolutions of the Heavenly Bodies_,
completed long before, but kept back for fear of the cry of novelty
and absurdity which, as he explains in his preface, dull men, ignorant
of mathematics, were sure to raise. The aged astronomer, paralysed and
dying, was able to hold his book in his hands before he passed away.
In the same year Vesalius, a young Belgian anatomist, published his
_Structure of the Human Body_, a volume rich in facts ascertained
by dissection. Some of these facts were held to contradict the teaching
of Galen. Next year Vesalius was driven by the hostility of the medical
profession to burn his manuscripts and relinquish original work; he was
not yet thirty years of age.
Galen had taught that there are two sets of vessels in the body
(arteries and veins), and that in each set there is an ebb and flow.
Knowing nothing of communications between the ultimate branches of
the arteries and veins, and shrinking from the supposition that the
arteries and veins are entirely separate and distinct, Galen had taught
that the blood passes from one set of vessels to the other in the
heart. The septum between the ventricles must be porous and allow the
blood to soak through. Vesalius did not venture openly to challenge the
physiology of Galen, but he significantly admired the "handiwork of
the Almighty," which enables the blood to pass from the right to the
left ventricle through a dense septum in which the eye can perceive no
openings. Fabricius of Acquapendente in 1574 demonstrated the valves of
the veins, though he never arrived at a true notion of their action.
His celebrated pupil, William Harvey, who had been anticipated on
important points by the Spaniard Michael Servetus and Realdo Columbo
of Cremona, published in 1628 a clear account, supported by adequate
experimental evidence, of the double circulation through the body and
the lungs, and of the communications between the arteries and the veins
in the tissues—communications which it was reserved for the next
generation to demonstrate by the microscope.
Aselli of Cremona rediscovered the lacteals in 1622; they had been
known ages before to Erasistratus, but forgotten. Opening the abdomen
of a dog, he saw a multitude of fine white threads scattered over the
mesentery, and observed that when one of them was pricked a liquid
resembling milk gushed out. Further examination showed him that these
vessels, like the veins, possess valves which permit flow in one
direction only. Pecquet, a French physician, announced in 1651 that
the lacteals open into a thoracic duct, which joins the venous system.
In 1653 Rudbeck of Upsala described yet another set of vessels, the
lymphatics; these again are provided with valves, and open into the
thoracic duct, but are filled with a clear liquid.
The effect of these discoveries upon physiology and medicine was
very great, but it did not end there; the whole circle of biological
students and a still wider circle of men who pursued other sciences
were thereby encouraged to follow the experimental path to knowledge.
Wallis, in describing the meetings of scientific men held in London
in 1645 and following years, mentions the circulation of the blood,
the valves in the veins, the lacteals, and the lymphatic vessels among
the subjects which had stirred their curiosity; while the naturalist
Ray thanked God for permitting him to see the vain philosophy which
had pervaded the University in his youth replaced by a new philosophy
based upon experiment—a philosophy which had established the weight
and spring of the air, invented the telescope and the microscope,
and demonstrated the circulation of the blood, the lacteals, and the
thoracic duct.
The Natural History of Distant Lands (Sixteenth Century and Earlier).
Travel and commerce had made the ancient world familiar with many
products of distant countries. Well-established trade routes kept
Europe in communication with Arabia, the Persian Gulf, and India.
Egyptians, Phœnicians, and Greeks explored every known sea, and
brought to Mediterranean ports a variety of foreign wares. Under the
Roman empire strange animals were imported to amuse the populace; silk,
pearls, gay plumage, dyes, and drugs to gratify the luxury of the rich.
Long after the fall of the empire foreign trade was kept up along the
coasts of the Mediterranean. Constantinople was still a great emporium.
Silk was not only imported from the East, but cultivated around
Constantinople in the sixth century. The cotton plant, the sugarcane,
the orange tree, and the lemon tree gradually spread northward and
westward until they became established in Italy, Spain, and the islands
of the Mediterranean.
Western Europe had during many centuries little share in this commerce.
The large and conspicuous animals of Africa and Asia, such as the
elephant, camel, camelopard, ostrich, pelican, parrot, and crocodile,
would have passed out of knowledge altogether but for chance mention
in the Bible and the Bestiaries. Little was done to supplement native
food-plants and drugs by imported products, and the knowledge of
foreign vegetation became as indistinct as that of foreign animals.
In the thirteenth century communication between Western Europe and the
far East was restored. China was thrown open by the Tartar conquest,
and Marco Polo was able to reach the court of Khan Kublai. Pilgrims
from the Holy Land brought back information which, however scanty it
might be, was eagerly received. One of the earliest printed books
(1486) contains the travels of Bernard of Breydenbach, a canon of
Mainz, whose narrative is adorned by curious woodcuts, in which we can
make out a giraffe and a long-tailed macaque.
The geographical discoveries of the sixteenth century gave men for the
first time a fairly complete notion of the planet which they inhabit.
Circumnavigators proved that it is really a globe. Maps of the world,
wonderfully exact considering the novelty of the information which they
embodied, were engraved as early as 1507. The explorers of America
busied themselves not only with the preparation of charts, the conquest
of Mexico and Peru, the search for gold, and the spread of the true
faith, but also with the strange animals and plants which they saw; and
the news which they brought back was eagerly received in Europe. Queen
Isabella charged Columbus, when he set out for his second voyage, to
bring her a collection of bird-skins; but this may be rather a proof
of her love of millinery than of her interest in natural history. Pope
Leo X. liked to read to his sister and the cardinals the Decades of
Peter Martyr Anglerius,[3] in which the productions of the New World
are described. The opossum, sloth, and ant-eater, the humming-bird,
macaw, and toucan, the boa, monitor, and iguana, were made known for
the first time. Potatoes and maize began to be cultivated in the south
of Europe, the tomato was a well-known garden plant, the prickly pear
was spreading along the shores of the Mediterranean, and tobacco was
largely imported. By the end of the seventeenth century Mirabilis and
the garden Tropæolum had been brought from Peru, the so-called African
marigold from Mexico, and sunflowers from North America. More than a
hundred years had still to run before the evening primrose, the passion
flower, and the lobelias of America were to become familiar to European
gardeners, ipecacuanha and cinchona to European physicians.
Agriculture, Horticulture, and Silk-Culture in the Sixteenth Century.
During the darkest parts of the Middle Ages agriculture and
horticulture were regularly practised. Tyranny, the greed of settlers,
the inroads of barbarians, private war, and superstition may destroy
all that brightens human life, but they hardly ever exterminate the
population of large districts,[4] and so long as men live they must
till the soil.
The age of Charlemagne was one of cruel hardship to the inhabitants of
Western Europe, but the cartularies of the great king show that the
improvement of horticulture was a matter of much concern with him. The
nobles and the religious houses kept trim gardens, which are delineated
in mediæval paintings. We know less about the state of the peasantry,
but it is clear that they ploughed, sowed, reaped, and dug their little
gardens, however uncertain the prospect of enjoying the produce of
their labour.
The progressive Middle Ages (about 1000 to 1500 A.D.) greatly
increased the comfort of the wealthy and alleviated the miseries of the
poor. We now hear of countries (England, the Low Countries, the western
half of Germany, the northern half of Italy) where freemen cultivated
their own land, or grew rich by trade, and these men were not content
barely to support life.
Under the later Plantagenets the wool-growers of that upland country
which stretches from Lincolnshire to the Bristol Channel showed
their wealth by building a profusion of manor-houses and beautiful
perpendicular churches, many of which still remain. There can be little
doubt that they were attentive to the rural industries which are so
great a source of comfort and pleasure.
In the sixteenth and seventeenth centuries the Flemings, a laborious
and enterprising people, inhabiting a fertile country, excelled the
rest of Europe in agriculture and horticulture. L'Obel, himself a
Fleming, speaks with pride of the live plants imported into Flanders
from Southern Europe, Asia, Africa, and America. By the close of the
sixteenth century, or a few years later, the lilac, lavender, marigold,
sun-flower, tulip, and crown-imperial, the cucumber and garden rhubarb,
besides many improved varieties of native vegetables, were sent out
from Flanders to all parts of Western Europe. During many generations
English agriculture and horticulture, and not these alone, but English
ship-building, navigation, engineering, and commerce as well, looked
to the Low Countries as the chief schools of invention and the chief
markets from which new products were to be obtained.
Late in the sixteenth century a gentleman of the Vivarais (the modern
Ardèche), named Olivier de Serres, wrote a book on the management of
land,[5] which leaves a strong impression of the zeal for improvement
which then pervaded Europe. De Serres was above all things intent upon
extending silk-culture in France.
On this topic he wrote with full knowledge, having reared silkworms for
thirty-five years. The King, Henri Quatre, shared his hopes, and gave
him practical encouragement. It is well known that a great industry was
thus started; by 1780 the annual yield of silk-cocoons in France was
valued at near a million sterling, while in 1848 it had risen to four
millions. De Serres sought to promote the cultivation of the mulberry
tree, not only because its leaves are the food of the silkworm, but
because he believed that the fibres of the bast would be serviceable
in the manufacture of cordage and cloth. He also tried to revive the
ancient practice of hatching eggs by artificial heat. We learn from him
that the turkey, recently introduced from Mexico, had already become
an important addition to the poultry-yard, while maize from Mexico and
beetroot from the Mediterranean coasts were profitable crops. Among
the new appliances De Serres mentions artificial meadows, wind and
water-mills, cisterns not hewn from stone, and greenhouses.
[1] Aristotle, Cesalpini, Gesner, and Ray are among the writers who use
this word or some synonym.
[2] It has now been made accessible to all readers by the reprint and
translation of Mr. A. H. Evans.
[3] Letter of Peter Martyr, Dec. 26, 1515.
[4] The extermination of the red man in North America is the most
conspicuous case recorded in history. Australia and Tasmania furnish
examples on a smaller scale.
[5] _Le Théâtre d'Agriculture_, 1600.
PERIOD II.
1661-1740
Characteristics of the Period.
In Western Europe this was a time of consolidation succeeding to one
of violent change. Religious wars gave place to dynastic and political
wars. In France the tumults of the preceding hundred years sank to rest
under the rule of a strong monarchy; order and refinement became the
paramount aims of the governing classes; literature, the fine arts, and
the sciences were patronised by the Court. Other nations imitated as
well as they could the example of France. Learning was still largely
classical, but the anti-scholastic revolt, which had first made itself
felt three hundred years earlier, steadily gained ground; Descartes,
Newton, and Locke were now more influential than the Aristotelians.
This was an age of new scientific societies (Royal Society, Academy of
Sciences of Paris, Academia Naturæ Curiosorum, etc.).
The Minute Anatomists.
Magnifying glasses are of considerable antiquity. Seneca mentions the
use of a glass globe filled with water in making small letters larger
and clearer. Roger Bacon (1276) describes crystal lenses which might
be used in reading by old men or those whose sight was impaired. As
soon as Galileo had constructed his first telescopes, he perceived that
a similar instrument might be caused to enlarge minute objects, and
made a microscope which revealed the structure of an insect's eye.
Within twenty years of this date the working opticians of Holland,
Paris, and London sold compound microscopes, which, though cumbrous
as well as optically defective, revealed many natural wonders to the
curious. Simple lenses, sometimes of high power, came before long to
be preferred by working naturalists, and it was with them that all the
best work of the seventeenth and eighteenth centuries was done.
The power of the microscope as an instrument of biological research was
in some measure revealed by Hooke's _Micrographia_ (1665). Robert
Hooke was a man of extraordinary ingenuity and scientific fertility, who
took a leading part in the early work of the Royal Society. He opens
his book with an account of the simple and the compound microscope of
his own day, and then goes on to explain, with the help of large and
elaborate engraved plates, the structure of a number of minute objects.
The most interesting are: A Foraminiferous shell, snow-crystals, a
thin section of cork showing its component cells, moulds, a bit of
Flustra, the under side of a nettle-leaf with its epidermic cells and
stinging-hairs, the structure of a feather, the foot of a fly, the
scales of a moth's wing, the eye of a fly, a gnat-larva, and a flea.
The beauty of the plates and the acuteness of some of the explanations
are remarkable, but lack of connection between the topics discussed
hinders the _Micrographia_ from rising to a very high scientific
level.
Swammerdam treated the microscope as an instrument of continuous
biological research. In his eyes it was a sacred duty to explore with
the utmost faithfulness the minute works of the Creator. Insects
yielded him an inexhaustible supply of natural contrivances, in which
closer scrutiny always brought to view still more exquisite adaptations
to the conditions of life. He was able to throw a beam of steady light
upon the perplexed question of insect-transformation, and swept from
his path the sophistries with which the philosophy of the schools had
obscured the change of the caterpillar into a moth, or of the tadpole
into a frog. He demonstrated the gradual progress of the apparently
sudden transformation of certain insects by dipping into boiling water
a full-fed caterpillar, and then exposing the parts of the moth or
butterfly, which had almost attained their complete form beneath the
larval skin; after this it was easy to discover the same parts in the
pupa.
There is no more valuable chapter in Swammerdam's great work, the
_Biblia Naturæ_, or Book of Nature, than that devoted to the
hive-bee. This insect had long been a favourite study, but only those
who were armed with a microscope and skilled in minute anatomy could
solve the many difficult questions with which it was involved. Aristotle
and other ancient naturalists had spoken of the _king_ of the bees,
which some bee-masters of the seventeenth century had been inclined to
call the queen. Was it really true that the queen was a female, perhaps
the only female in the hive? This question Swammerdam decided by the
clearest anatomical proof—viz., by dissecting out her ovaries. He
pointed out the resemblances between the queen and the workers, such
as the possession of a sting by both, but did not discover the reduced
reproductive organs of the workers, and wrongly declared that they
never lay eggs. He proved by elaborate dissections that the drones are
the males of the community. How and when the queen is fertilised he
could not make out.
[Illustration: MARCELLO MALPIGHI
From an engraving of the oil-painting by A. M. Tobar, presented
to the Royal Society by Malpighi.]
The dissection of the sting, the proboscis, and the compound eye
of the bee was a task after Swammerdam's own heart, but so intricate
that all his patience and skill could not save him from occasional
slips. He bequeathed to his successors many noble examples of the way
in which life-histories ought to be investigated.