Chapter I: Part 1

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1. Typographical errors have been silently corrected.

2. Variations of spelling and hyphenation are as in the original.

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(_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.

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.

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.

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.

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.

Malpighi of Bologna may be called the first of the histologists, for as early as the second half of the seventeenth century he unravelled the tissues of many animals and plants. His work on plant-tissues was so closely accompanied by the similar researches of an Englishman, Nehemiah Grew, that it is not easy to assign the priority to either. Malpighi was the first to demonstrate the capillaries which connect the arteries with the veins, the first to investigate the glands of the human body and the sensory papillæ of the skin. At the request of our Royal Society he drew up an account of the structure and life-history of the silkworm, which is memorable as the earliest anatomical study of any insect. Malpighi also applied his microscope to the chick-embryo, and figured its chief stages. His exposition of the formation of the heart and vessels of the chick is a marvellous example of the quick appreciation of novel structures.

If we suppose the _Micrographia_ of Hooke to be greatly enlarged, so as to become, instead of the passing occupation of a man busied with a hundred other interests, the main pursuit of a long and laborious life, we shall get a rough notion of the microscopic revelations of Leeuwenhoek. His researches were desultory, though not quite so desultory as Hooke's; he must have often spent months upon an investigation which Hooke would have dismissed in as many weeks. Both travelled over the whole realm of nature, and lacked that concentration which made the work of Swammerdam so productive and so lasting.

Leeuwenhoek worked with simple lenses, ground and mounted by his own hands. It was easy to make lenses of high magnifying power, but hard to correct their optical defects, to bring a sufficiently strong light to bear upon the object, and to focus the lens. When he wished to send out his preparations for examination by others, he found it best to fix the objects in the focus, and to provide each with a separate lens. With such microscopes he managed to study and figure very minute objects, such as blood-corpuscles, spermatozoa, and bacteria. The spermatozoa were brought under his notice by a young Dutch physician named Hamm; but it was Leeuwenhoek's account of them, and his daring theory of their physiological _rôle_, which gave them such celebrity. To Leeuwenhoek we owe the first discovery of the rotifers, the infusoria, Hydra, the yeast-cell, the bacteria, and the generation of aphids without male parents.

The tradition of the minute anatomists has never been lost, though we shall be unable to pursue it in these pages. Lyonet (see p. 61) even surpassed Swammerdam in the elaborate finish of some of his insect-dissections.

Early Notions about the Nature of Fossils.

Throughout the sixteenth century naturalists held animated debates about the shells which are found far from the sea, and even on the top of high hills. Had they ever formed part of living animals or not? Such a question could hardly have been seriously discussed among simple-minded people; but the learned men of the sixteenth century were rarely simple-minded. They had been trained to argue, and argument could make it plausible that such shapes as these were generated by fermentation or by the influence of the stars. So prevalent were these doctrines that it entitles any early philosopher to the respect of later generations that he should have taken shells, bones, and teeth to be evidences of animal life. In this singular roll of honour we find the names of Cesalpini, Palissy, Scilla, Stenson, Hooke, and Woodward.

In England the struggle between philosophy and common-sense was long kept up. Dr. Ralph Cudworth of Cambridge taught that there is in nature a subordinate creative force of limited power and wisdom, to whose imperfections may be attributed the "errors and bungles" which now and then mar the work. To this subordinate creative force he gave the name of "vegetative soul," or "plastic nature." None but Cambridge men, it would appear, felt the weight of Cudworth's reasoning; but several of these, and especially John Ray[6] and Martin Lister, defended his conclusions in published treatises. Lister, in a chapter devoted to "cochlites," or shell-shaped stones, pointed out that they differ from true shells in being of larger size, in occurring far from the sea, in being formed of mere stony substance, and in being often imperfect. Some naturalists had conjectured that the living animals of the cochlites still exist at great depths in the sea, but Lister evidently thought otherwise.

In the eighteenth century the belief that fossils are the remains of actual animals and plants more and more prevailed, the death and sealing up of the organisms being generally attributed to Noah's flood. The occurrence of fossils on high mountains seemed so strong a confirmation of the Biblical narrative that Voltaire was driven to invent puerile explanations in order to dispel an inference so unwelcome to him. By the end of the century most naturalists accepted the doctrine that the great majority of fossils are the remains of organisms now extinct—a doctrine which was enforced by the remarkable discoveries of Cuvier (see p. 93). Nearly at the same time William Smith established the important truth that almost every fossil marks with considerable precision a particular stage in the earth's history.

Comparative Anatomy: the Study of Biological Types.

Between 1660 and 1740 the scope of natural history became sensibly enlarged. System had been hitherto predominant, but the systems had been partial, treating the vertebrate animals and the flowering plants with as much detail as the state of knowledge allowed, but almost ignoring the invertebrates and the cryptogams. System was now studied more eagerly than ever by such naturalists as Ray and Linnæus, but new aspects of natural history were considered, new methods practised, new groups of organisms included. Many remarkable vertebrates were anatomically examined for the first time. Claude Perrault and his colleagues of the Académie des Sciences dissected animals which had died in the royal menagerie, and compared the parts and organs of one animal with those of another; Duverney compared the paw of the lion with the human hand; in England Tyson studied the anatomy of the chimpanzee, porpoise, opossum, and rattlesnake, searching everywhere for the transitions which he believed to connect all organisms, and to form "Nature's Clew in this wonderful labyrinth of the Creation." The new microscopes helped to bring the lower and smaller animals into notice. From 1669, when Malpighi described the anatomy and life-history of the silkworm, a succession of what we now call biological types were studied; among these were many invertebrates. Edmund King and John Master contributed to Willis's treatise _De Anima Brutorum_ (1672) the anatomies of the oyster, crayfish, and earthworm, all illustrated by clear and useful plates. Heide (1683) wrote an account of the structure of the edible mussel (Mytilus), in which mention is made of the ciliary motion in the gill; Poupart (1706) and Méry (1710) wrote accounts of the pond-mussel (Anodon). Swammerdam's elaborate studies of insects and their transformations were followed up by a long succession of memoirs by Frisch in Germany, Réaumur in France, and (shortly after the close of the period now under discussion) De Geer in Sweden. The extraordinary diligence and power of Swammerdam and Réaumur give a very prominent place in the biology of the seventeenth and eighteenth centuries to the structure and life-histories of insects. The great generalisations of comparative anatomy do not belong to this period; nevertheless, sagacious and luminous remarks are not wanting.

Adaptations of Plants and Animals: Natural Theology.

Natural adaptations and some of the problems which they suggest were much studied during this period. Bock and Cesalpini had discussed still earlier the mechanisms of climbing plants, aquatic plants, and plants which throw their seeds to a distance. Swammerdam figured, not for the first time, the sporangia and spores of a fern; Hooke the peristome of a moss. The early volumes of the Académie des Sciences contain many studies of natural contrivances. Perrault described the retractile claw of the lion, the pointed papillæ on its tongue, the ruminant stomach and the spiral valve of a shark's intestine. He improved upon Hooke's account of the structure of a feather, and his magnified figures of a bit of an ordinary quill and of a bit of an ostrich-plume might be inserted into any modern treatise on animal structure.[7] Poupart followed the later stages of the development of a feather. Méry gave a minute yet animated description of the wood-pecker's tongue, explaining how it is rendered effective for the picking up of insects, how it is protruded and retracted, how it is stowed away when not in use. Tournefort figured the oblique fibres of a leguminous pod, which he called _muscles_, and showed how they twist the valves and squeeze out the seeds.