APPLICATIONS OF BIOLOGY It is useful, theoretically at least, to distinguish applied biology from applied zoology and applied botany. When means are taken to check the spread of injurious insects, or the dissemination of malaria by mosquitoes and of sleeping sickness by tsetse flies, or the damage done by parasites such as the hook-worm in man or the Isle-of-Wight mite (Acarapis) in hive-bees, there is an appli cation of zoology to a practical problem. The success of the check often depends on a knowledge of the life-history and inter-rela tions of the animals involved. Similarly, there is an application of botany in the effort to check the diffusion of plant-diseases and plant-enemies. As regards man himself, as well as his domesti cated animals and cultivated plants, great results have rewarded applied botany and applied zoology. But applied biology is some what different ; it implies the application of general biological ideas, not the specialist's knowledge of this or that animal. Thus Mendelism (q.v.) applied to plants and animals is applied biology, and so is the general policy of hygiene and eugenics. An apprecia tion of the general biological idea of the web of life might have saved man from some of his short-sighted introductions and elim inations, and may assist him in his policy of more economically exploiting the life of land and sea. In coping with the bilharzia parasite in detail there is co-operation between medicine and zoology, but the idea of acting on a knowledge of the linkage between the man and his worm, on the one hand, and between water-lilies and aquatic birds on the other, comes as a suggestion from biology.
While the biologist has come to understand how certain kinds of variations or new departures may arise, e.g., by a shuffling of the hereditary cards contained in the chromosomes, or by the interpenetration of some potent environmental influence, it is not possible at present to give any clear account of the origin of a large mutation of a distinctly novel character, though H. G. Muller and others have succeeded in producing large mutations by X-ray irra diation. Yet the origin of the new is the central and inevitable problem of biology. Similarly, while the secure data of Men delian inheritance have grown in volume with remarkable rapidity, it does not appear to be possible at present to give any reason why one of two contrasted characters should be dominant and the other recessive. On another line, it may be said that some biologists who regard the evidence in favour of Lamarckism as altogether un convincing, are willing to admit the reality of certain puzzling phenomena which demand further inquiry and some fresh dis covery. But the whole subject of organic evolution bristles with unsolved problems! Returning to the concrete, we may illustrate the kind of un solved problem to which we specially refer by mentioning the way-finding capacities exhibited by migratory birds. Prolonged experiments with ants and bees seem to have proved that in the majority of cases at this level there is an individual learning of the topography around the hill or hive. But this does not apply to cases like the sooty and noddy terns of the Tortugas which are able in some cases to return to their nests after being transported in closed baskets for a thousand miles and liberated in seas pre viously unknown.
Life is a particular kind of activity exhibited by living crea tures. It includes many chemical and physical processes which become more clearly known every year. But these processes of oxidation and fermentation, of surface tension and osmosis, of heat-production and electric discharge, and so forth, are cor related, regulated, controlled and integrated; and it is this unifica tion, leading to effective behaviour, which seems at present to be indescribable in terms of chemical and physical concepts. These have been for the most part developed in reference to changes of matter and energy in circumstances not including life, and it is not to be expected that they should apply to the totality of reac tions exhibited in another order of facts, namely those of organ isms. It is not behaviour alone that stands by itself, but the capacity for growth, multiplication, development and enregistra tion. As W. K. Clifford said: "It is the peculiarity of living things not merely that they change under the influence of sur rounding circumstances, but that any change in them is not lost, but retained, and, as it were, built into the organism to serve as a foundation for future actions." Since the living organism appears to be a new synthesis, as compared with a stone or a star or a drop of colloidal matter, since it exhibits qualities that cannot be adequately described in terms of matter and energy, it seems good sense to claim some autonomy for biology. The organism is a new synthesis in which certain aspects of reality, previously un expressed, find expression, and these cannot be adequately de scribed without the use of special biological concepts, such as irritability and enregistration, growth and development, and effec tive behaviour.
Among birds and mammals there is abundant evidence of the intelligent control of behaviour in reference to a perceived pur pose. There is often more than a hint of judgment ; endeavour is undeniable; feeling is often strong. The biologist must recognize that he is dealing with psycho-biosis. A Robot theory of the higher animal does not work, and recent well-criticized observa tions and experiments on the highest apes show that the level of intelligence is higher than the most generous had supposed. On the other hand, there is not less abundant evidence that no small part of animal activity depends on automatic reactions, tropisms, enregistrations and reflexes, both unconditioned and conditioned. It may be said, indeed, that animal behaviour has evolved along two main lines. On the one hand, there is the evolution of the power of fresh adjustment, of making little experiments or tenta tives. This is the line of individual initiative and it has its climax in sheer intelligence. On the other hand, there is the evolution of the capacity for the neural enregistration of profitable modes of behaviour, so that they become parts of the inheritance, requiring no more than a liberating stimulus for their activation. In both cases there is inherited capacity, but among "big-brained types," as Sir Ray Lankester has called them, the inheritance is mainly a nimble, plastic, educable intelligence, while among "little brained types" the inheritance is mainly a stereotyped series of reactions. Now it is one of the major problems of biology to do justice to these two lines, a problem which is the more difficult since they sometimes intersect.
But the attempt to do this is likely to bring the biologist face to face with the still more difficult problem of the relation be tween body and mind. On the one hand, there is the bodily, the nervous, the physiological, the objective. On the other hand, cor related yet incommensurable, there is the mental, the psychical, the psychological, the subjective. How are these two aspects of reality to be thought of in relation to one another? When are we warranted in stressing the one, and when the other? It re mains a difficult problem for the biologist to trace the expressions of mentality backwards to their slender beginnings, both in the individual higher form and in the animal kingdom as a whole ; and to probe further back still to what may have corresponded to mind in the non-living materials out of which organisms may have evolved. It seems necessary to assume that a certain degree of organismal intricacy is necessary, both in ontogeny and in phylog eny, before emergence is possible for that aspect of reality which we call "mind," an aspect which is of such predominant impor tance in the development of The Sociosphere.
In the living body there are diverse processes of oxidation and reduction, hydration and dehydration, solution and fermenta tion and so forth, which can be taken separately and studied by the bio-chemist. Similarly there are phenomena of surface ten sion, capillarity, osmosis, leverage, hydrodynamics, thermody namics, electricity and so forth, which can be taken seriatim and studied by the biophysicist. Biophysical and biochemical methods have helped greatly towards a better understanding of the life of the body. They illustrate what Comte called a legitimate and necessary materialism. Biology cannot dispense with the assis tance of the more exact sciences. But, even if we had a complete ledger of all the biochemical and biophysical processes that occur when a swallow returns from the Gold Coast to the place of its birth in a Scotch farm-stead, we should not understand the bird's remarkable homing. For that requires distinctively biological con cepts. The concepts of chemistry and physics are indispensable in biology, but biology transcends them and requires concepts of its own. The organism transcends mechanism and is a "historic being." The inter-relation of "body" and "mind" is such as to justify the saying : nemo psycliologus nisi physiologus; but we sometimes for get to transpose this. An emotional storm stimulates the produc tion and distribution of adrenalin ; dyspepsia warps the judgment and dulls good feeling. A blot in the brain may mean a darkening of the eyes of the mind ; and the clinical biographies tell us how an eye-trouble may ruin a man's temper. Yet a merry heart is the life of the flesh and good news promotes digestion. Mental and bodily, psychical and neural, subjective and objective are so closely intertwined that it seems to many biologists that their science is really psycho-biology. Similarly, but more distantly, in regard to sociology, the biological foundations cannot be ignored without loss. The units in sociology are societary groups of some sort, but these consist of individuals with all the appetencies and limitations of organisms. There is a social aspect of heredity, of sex, of multiplication and of nutrition. Just as there can be no sound biology that does not keep continually in view the three sides of the prism, Organism, Functioning and Environment, so there can be no sound sociology that does not keep continually in view the social analogues of these : Leplay's "Famille, Travail, Lieu." Here the biologist and the sociologist join hands.
(See ZOOLOGY, BOTANY, PHYSIOLOGY, PALAEONTOLOGY, PALAEO BOTANY, EVOLUTION, SPECIES, etc.) BIBLIOGRAPHY.-J. A. Thomson, The Science of Life (Glasgow, Bibliography.-J. A. Thomson, The Science of Life (Glasgow, 1899), The System of Animal Nature (192o) and Everyday Biology (1923) ; Herbert Spencer, The Principles of Biology (1908) ; J. G. Needham, General Biology (Ithaca, 191o) ; K. Pearson, The Grammar of Science (191I) ; G. N. Calkins, Biology (1914) ; J. Loeb, The Organism as a Whole (1916) ; E. S. Russell, Form and Function (1916) and The Study of Living Things (1924) ; D'A W. Thompson, On Growth and Form (Cambridge, 1917) ; J. S. Haldane, The New Physiology (1919) ; L. L. Woodruff, Foundations of Biology (192 2) ; F. Bower, Botany of the Living Plant (1923) ; A. Dendy, Evolutionary Biology (1923) ; C. Lloyd Morgan, Emergent Evolution (1923) ; A. Shipley, Life (Cambridge, 1923) ; MacGregor Skene, The Biology of the Flowering Plant (1924) ; P. Geddes and J. A. Thomson, Biology (1925) ; C. Elton, Animal Ecology (1927) ; J. B. S. Haldane and J. S. Huxley, Animal Biology (Oxford, 1927) ; C. G. Rogers, Comparative Physiology (1927) ; J. von Uexkiill, Theoretical Biology (5927).
Biology, in the widest acceptance of the word, is used to cover all those studies which deal with the structure, nature and be haviour of living beings. It is thus in contrast to the word physics which is similarly used to cover the study of the structure, nature and properties of such matter as is neither living nor a necessary product of the activity of living things. It happens that certain of the studies classed as "biological" are intimately bound up with the study of medicine. Such are, for example, human anatomy, the physiology of the warm-blooded animals, bacteriol ogy and the like. The linking of these departments with medical study has had certain historical and practical results and they are sometimes tacitly excluded from what is called biology in cer tain narrowed academic uses of that term. As a matter of prac tical convenience these departments have been considered in the article MEDICINE, HISTORY OF. Here we shall only consider them incidentally.
The word biology was introduced by S. T. Treviranus (1776– 183 7) in his Biologie oder die Philosophic der lebenden Natur (Gottingen, 1802-22). It was adopted and popularized by J. B. de Lamarck (1744-1829, q.v.) in his Hydrogeologic (Paris, 1802) . It is probable that the first English use of the word in its modern sense was by Sir William Lawrence (1783-1867) in his work On the Physiology, Zoology and Natural History of Man (London, 1819) . There are, indeed, earlier uses of the word in English but they are in relation to biography.
Biology, like other sciences, can be traced to the Greeks. At a very early date, and particularly at the hands of Alcmaeon of Croton (c. 500 B.C. q.v.), we hear of independent investigations of the structure and habits of animals. Thus Alcmaeon described the optic nerves and tubes that lead from the nose to the ear (Eustachian tubes), and he made a beginning of the study of the development of the embryo. Moreover, the Hippocratic collec tion (see MEDICINE, HISTORY OF and HIPPOCRATES) provides evi dence, imbedded in a work on diet, of the existence of attempts to make a classification of animals as early as the 5th century B.C. All the early records of biological science before the 4th century B.C. are, however, either completely lost or too fragmen tary to permit of adequate reconstruction. Not until we get to Aristotle (384-322 B.c.) do we encounter any complete biological works. Moreover, as our knowledge of Greek biological science begins with Aristotle, so it may almost be said to end with him. The only surviving ancient works on living things, besides those of Aristotle, that were prepared without consideration of the application of the knowledge they set forth, are by his pupil, Theophrastus. A full account of the biological achievements of Aristotle and of Theophrastus would thus contain an almost complete account of our knowledge of pure biological science as it existed in antiquity.
There are matters in these works which come rather in the department of philosophy than in that of biology (see ARISTOTLE) but which must nevertheless of necessity be considered in any account of the history of biological thought which they have influenced throughout its course. Among these matters is Aris totle's conception of the nature of the living principle or psyche.
The oldest use of the word "psyche" is in the sense of breath, and breathing is the most obvious sign of life. It was, therefore, natural that from breath the word psyche came to mean life, then the soul and again the mind. Aristotle used this term for the principle that differentiates living from not-living substance When he began to examine different living things he reached the conclusion that there were different kinds or orders of psyche or soul. In the course of this investigation he came to distinguish between (a) the vegetative soul, (b) the animal soul, (c) the rational soul.
The first or lowest of these was the vegetative soul. Aristotle regarded plants as the lowest living forms and the qualities of life that he distinguished in plants he regarded as the only qual ities essential for this lowest form of soul. These qualities seemed to him to be nutrition. growth and the power of reproduction.
Aristotle considered that while animals had these qualities of the vegetative soul, they also had, of their nature, the power of movement, and the movements that they made seemed to him to correspond to what they felt. The animal soul thus possessed, as he thought, not only the qualities of the vegetative soul but also a second order of qualities which were responsible for the sensi tive and motive powers of animals.
Lastly, man had all these qualities exhibited in the lowest creation, both plants and animals, but he had also certain others. He could reason and his movements and actions were dictated by his thoughts. His soul was, therefore, equipped, in Aristotle's view, not only with the qualities of the vegetative and animal souls, but also with rational or intellectual powers.
It will thus be seen that Aristotle was, in the fullest and most definite sense, a "vitalist." Apart from the classification of kinds of soul Aristotle held certain definite views as to the relationship of this soul or psyche to the living body. This relationship was determined by the existence of an Entelechy, a term which may perhaps be translated for biological purposes as "an indwelling purposiveness." The nature of this Entelechy is perhaps best brought out by quotation from his work De Anima, from which it will be gathered that he held that the soul is neither independent of, nor is it identical with, the body.
"They are right," says Aristotle, "who hold the soul as not independent of the body and yet as not in itself anything of the nature of the body. It is not body, but something belonging to body. It, therefore, resides in body, and moreover, a particular soul to a particular body. They were wrong who sought to fit the soul into the body without regard to the nature and qualities of that body. For the Entelechy of each thing comes naturally to be developed in the potentiality of each thing, and it is manifest that soul is a certain Entelechy and notional form of that which has the capacity to be endowed with soul." This, then, is the basic thought in Aristotle's biological work, and in this sense Aristotle is a modern biologist, for it is the basic thought in much biological work at the present day. But besides Aristotle's finely wrought out biological theories, of which this is one, there is much in his biological writing that does not involve these high topics, but is restricted to the ordinary investi gations of the working biologist as we know him in our own time. Foremost among these investigations on the phenomenological level we may note Aristotle's magnificent observations on the habits of fishes, some of which, doubted for centuries, have been verified in our own time. No less remarkable are his observations on the breeding and development of the octopuses and their allies. His discourses on whales, porpoises and dolphins, on the develop ment of dog-fish, and on the habits of bees are also very note worthy. There is much in his writings to justify us in classing Aristotle as one of the best observing naturalists of all time.
The whole course of biology may be represented as the history of ideas on the classification of living things. Something must be said on this subject in relationship to Aristotle.
At first, Aristotle entirely separated man from the lower crea tures, distinguishing him among living things by the possession of a rational soul. As Aristotle's knowledge increased, he seems to have become less inclined to make this absolute distinction and he came to admit that animals in their degree share rationality with man. His final position seems to have been that the dis tinction between the animal and the rational soul cannot be con sistently maintained and that there is no fundamental distinction between life or soul and mind. This is precisely the attitude of an important school of modern biologists.
In ascribing reason to animals Aristotle seems to have been influenced by his advance towards something that we should nowadays call a belief in "Evolution." It cannot justly be said that he ever attained to a clear view of organic evolution. Never theless, it is evident that he was moving in that direction, that he was not far from reaching it and that had he lived a few years more it might well have been that he would have reached it. But whether we call him an evolutionist or whether we withhold that title from him, it is certainly easy to read an evolutionary meaning into much of his biological writings. Moreover, we see him groping at some natural manner of arranging the orders of animals. He is, in fact, striving towards what we should call a "classification." The mechanism that he actually adopted was to arrange living things in a sort of scale. This Scala Naturae of Aristotle is a subject of great interest and is worthy of all possible respect. He describes a particular part of this as follows: "Nature proceeds little by little from things lifeless to animal life in such a way that it is impossible to determine the exact line of demarcation, nor on which side thereof an intermediate form should lie. Thus next after lifeless things in the upward scale comes the plant. . . . Of plants one differs from another as to its amount of apparent vitality. In fact, the whole of plant kind, while devoid of life as compared with animals, is endowed with life as compared with other forms of matter. Therefore, there is in plants a continuous scale of ascent towards the animal, and of some, one is at a loss to say whether they be animal or plant. • • • Thus nature passes from lifeless objects to animals in unbroken sequence, so that scarcely any difference seems to exist between two neighbouring groups by reason of their close prox imity." As a working naturalist Aristotle excelled chiefly in his obser vations on the habits and lives of animals. He was less fortunate in his investigations of their structure, and less fortunate still in his consideration of the functions of parts. He was, in fact, far less an experimenter than an observer. This is not surprising since he had no exact body of knowledge of experimental physics and chemistry on which to build. Some of his successors among the Greeks, e.g., Galen, far excelled him in their experimental skill and ingenuity.
Theophrastus understood the value of developmental study, a conception derived from his master. "A plant," he says, "has the power of germination in all its parts for it has life in them all, wherefore we should regard them, not for what they are, but for what they are becoming." He lays much stress on the different modes of reproduction of plants. He distinguishes between the monocotyledons and the dicotyledons, and he has some interesting passages in which sex is discerned in plants, notably in the palms.
The works of Theophrastus are extremely valuable as perhaps the most complete biological treatises that have come down to us from antiquity. They contain many excellent observations, but are on the whole distinctly inferior in depth, range and insight to the biological works of Aristotle.
Pure biological investigation virtually came to an end with the death of Theophrastus. Biology was studied at the Alexandrian school, but chiefly in connection with medicine and has been con sidered elsewhere (see MEDICINE, HISTORY OF). There was one important development, however, in Alexandrian times to which we may refer. This was the practice of portraying the forms of plants exactly and artistically. It seems probable that science owes this most important accessory art to one Crateuas, a herb alist who practised in the 1st century B.C. There are reasons for believing that we have accurate copies of some of the drawings of this artist, and these copies are therefore of the utmost interest to biologists.
The Hellenistic investigator, whose writings have had most influence on the course of botany, and in particular on botanical terminology, is the physician Dioscorides of Anazarba in Asia Minor. Dioscorides served in the army of the emperor Nero, and a work by him on plants useful in medicine has come down to us in great completeness and in a very large number of manu scripts. Nevertheless, this work is ill arranged, almost devoid of general ideas and steeped in the errors that must always pursue those who follow purely practical ends without regard to theoreti cal considerations. The work of Dioscorides is essentially a drug collector's manual, and represents a very great deterioration from the Aristotelian standard.
Even lower in quality than the De materia medics of Dioscor ides is the Natural History of his contemporary, Pliny the elder (died A.D. 79). It is immensely interesting as a storehouse of folk-lore and as a mirror of the follies and superstitions of his age. It cannot be passed over in silence since it was perhaps more read during the middle ages than any work of antiquity except the Bible. From the point of view of a rational development of biological thought, however, Pliny's work is beneath contempt.
The only other important later figure in the biological thought of antiquity is Galen. The magnificent apparatus and achieve ments of this man have been considered elsewhere (see GALEN and MEDICINE, HISTORY OF). Though his interests were mainly medi cal, the vigour and independence with which he pursued his re searches give him a very important place in the history of biology.
After Galen, the history of biological thought is a dismal record of steady deterioration for many centuries. Even with the great scholastic and artistic revival of the 13th century, there is little evidence of any systematic firsthand observation. Still less is there any trace of independent biological thought. We do no grave injustice to any writer in passing direct to the revival of learning.
The great artists of the Renaissance period, Botticelli, Leonardo da Vinci, Diirer, Michelangelo and others, exhibited an interest in the exact portrayal of animal and plant forms as well as curios ity as to the structure of the human body. As well as being artists these great Renaissance figures were all of them curious as to the ways of nature, and it is not misusing words to speak of these artists as men of science, botanists, anatomists, physiologists and the like. The group of movements which came to flower with the beginning of the 16th century placed the student of nature in a peculiarly favourable position. He had the works of science of antiquity on which to start. The craft of printing was at his disposal. He had the scientific studies of the great artists before him. He had learnt to represent details of nature effectively. At last, also, the art of the wood-cutter was perfected, so that the figures of the artist could be transferred to the printed page.
It was in this happy collocation of circumstances that the first effective biological textbooks of modern times were produced. The movement began in Germany and it began with the botanists. It is the distinction of Otto Brunfels (1464-1534) that he pro duced the first printed work on plants which relied solely on observation. The drawings are firm and faithful and it is very interesting to compare them with those of a good modern text book. As Brunfels was the first, so Leonard Fuchs (15o r-66) was the greatest, of the German "fathers of botany." His work appeared in 1542 and is the landmark in the history of natural knowledge.
A part of the same movement illustrated by the "fathers of botany" is the new scientific interest in anatomy. Protagonists of that movement (see MEDICINE, HISTORY OF) are Andreas Vesalius and Bartolomeo Eustachio. More in the class of pure "naturalists" in the modern acceptance of that word were the two French observers, Belon and Rondelet.
Pierre Belon (1517-64) of Le Mans spent some years wander ing in the Near East. He kept careful notes of the natural history of the countries that he traversed, basing his observations on his reading of Aristotle. Later he produced two books on fishes and another on birds, which, though borrowing much from Aristotle.
show also much original observation. It is interesting to note the clearness with which Belon grasps the general principles of com parative anatomy, especially as applied to the skeleton. These principles had already been elucidated by Vesalius. More accurate as an observer, though less imbued with comparative principles was Guillaume Rondelet (15°7-66) of Montpellier, a friend of Rabelais. Rondelet's great work is a painstaking investigation of the fishes of the Mediterranean.
The learning of the time was liable to express itself in the form of encyclopaedias. These were mostly little but compilation. An exception must be made, however, for that of Conrad Gesner 0516-65), the great Swiss naturalist. His history of animals in five folio volumes covers the topics of quadrupeds, birds, fishes and snakes. Most of the matter is borrowed, but much also is original, notably the section on fishes which contains also figures of a large number of invertebrates. The work of Gesner is re garded by many as the starting point of modern zoology. To his contemporaries, Gesner was best known as a botanist, but his most important botanical works were not published until 200 years after his death.
Towards the end of the i6th century, following on the stimulus of the revival of art, of the new interest in natural history and of the re-institution of scientific anatomical studies, all the important departments of biology—anatomy, physiology, botany, zoology— were becoming differentiated and making considerable progress. These subjects were being taught especially in the universities of northern Italy. Nowhere were they prosecuted with greater en ergy and ability than at Padua, the old school of Vesalius. Of all the teachers of that school, Jerome Fabricius (1537-1619) of Aquapendente exercised most influence. Fabricius made extensive embryological investigations, and his works on the subject are the first to be illustrated with figures drawn from the object. He made many physiological researches. Thus he described the valves of the veins and was one of the first to give an accurate account of the structure of the eye. Other important Paduan teachers of the time were Realdo, Colombo, Sanctorio, Cesalpino and Casserio.
The Rebirth of the Physiological Study of Animals and Plants.—A remarkable pupil of Fabricius was the Englishman, William Harvey (1578-1657), the discoverer of the circulation of the blood. His work on that subject, published in 1628, gave the first rational explanation of the workings of the animal body. (See MEDICINE, HISTORY OF, and HARVEY, WILLIAM.) While Har vey was at work on the special researches which are associated with his name, optical instruments were being constructed which made it possible to examine the structure of animals more minutely. In 1610 the compound microscope was described by Galileo and through him passed into modern use. The first sys tematic investigation of living things with the new instrument was made by a group of young men who formed themselves into the first scientific society, under the name of the Academy of the Lynx, which usually met at Rome. The small company was accustomed to assemble at the house of its president, Prince Federigo Cesi, duke of Aquasparta. His early death in 1628 brought the academy to an end, and many of its works perished. We have, however, records of a few of its observations which are peculiarly interesting as the earliest for which the microscope was systematically employed. Prince Cesi himself worked on botanical topics and described and portrayed the spores of the fern. Other members of the academy applied themselves to animal forms and fine enlarged representations of the parts of the bee have come down to us from them.
With the collapse of the "Academy of the Lynx" systematic microscopical observation ceased for a generation. The micro scopic work between 1628 and 166o was desultory and of no great consequence. After that date, however, there arose a series of great microscopical observers who between them revolutionized the conception of the nature of living things. Of these "classical microscopists" two, Hooke and Grew, were English, two, Leeuwen hoek and Swammerdam, were Dutch, and one, Malpighi, was Italian. It is interesting to observe that the more important work of all of them, except Swammerdam, was published in England.
Marcello Malpighi (1628-94) supplemented Harvey's work by describing the capillary circulation which Harvey had not seen. Malpighi demonstrated it in the lung of the frog. He extended greatly the work of Fabricius and he especially investigated the early stages of the development of the embryo of the chick. He gave very accurate representations of the early stages, and not ably he showed that in the embryo there are paired branches of the aorta which reunite. These correspond, as we now know, to the vessels in the gills of a fish. Malpighi, who had no evolution ary leanings, had no conception of the nature of these vessels, but his description of them is very good. The bulkiest of Ma lpighi's contributions are his writings on the anatomy of plants. He gave excellent representations of the cell walls of plants, and he estab lished the broad outlines of the microscopic anatomy of the roots and stems of the higher plants.
In botanical anatomy even more accurate and systematic obser vations were made by Nehemiah Grew (1641-1712, q.v.). Grew placed the study of the anatomy of plants on a firm foundation. He is also remarkable for his statement as to the sexual character of flowers—an observation which he himself ascribes to Sir Thomas Milligan, Savilian professor of geometry at Oxford.
Jan Jacob Swammerdam (1637-8o, q.v.) was perhaps, the most accurate and remarkable as he was the most mentally un stable and shortlived of the "classical microscopists." His first work, A General History of Insects, deals chiefly with the modes of transformation of insects and brings out well the different modes of development of the major groups of insects. The text and figures are equally good, and the book itself obtained popu lar recognition. The early onset of a state of mind not far from insanity prevented much further publication. His magnificent Bible of Nature, which is probably the finest collection of micro scopical observations 'ever published, did not appear till long after his death. It is still in current use by naturalists.
Antony van Leeuwenhoek (1632-1723, q.v.) made the most impression on his contemporaries of all the "classical micro scopists." He published an immense number of observations of a desultory kind, nearly all of them in the Philosophical Transac tions of the Royal Society. These observations contain many shrewd judgments. Leeuwenhoek's portrayal of Bacteria in 1683 and of spermatozoa in 1677 are triumphs of observation with the optical means at his disposal. On several occasions he drew and described the structure of striated muscle. He investigated in his own peculiar fashion almost every department of animal and plant life. No one was more influential than Leeuwenhoek in drawing the attention of observers to the minute complexity and beauty of the structure of the animal body.
Of all the "classical microscopists" the most gifted was Robert Hooke (1635-17°3). He was, however, only to a very limited extent a biologist. His important work, Micrographia, appeared in London in 1665. In it he has a figure of the microscopic structure of cork showing the boundaries of the cell walls. He refers to these as cellulae, and the word "cell" in our modern biological nomenclature is probably derived from him. He shows also the cells on the surface of the stinging nettle, and he has a good account of its stinging apparatus. An importa,nt botanical obser vation by him is on leaf fungus, the development of which is well shown. He also gives accounts of the development of a mould and of the structure of moss, and of experiments on the sensitive plant. He gives the first figures of a polyzoan, and remarkable delineations of the compound eye of an insect, and of the larvae of a gnat, besides two gigantic figures of a flea and of a louse.
The work of the "classical microscopists" stands somewhat apart from that of other investigators and forms a peculiarly isolated chapter in the history of biology.
The first trace of any systematic arrangement of descriptions of plants in accordance with their structure is in the work of Matthias de l'Obel (1538-1616), a Dutchman who came to Eng land in his youth and dedicated his first book (15 70) to Queen Elizabeth. He was keeper of a botanic garden of an English peer and, later, botanist to James I. L'Obel attempted to group plants according to the form of their leaves. He succeeded fairly well with the grasses, less well with the monocotyledons and failed with the dicotyledons, with which he confused the ferns. More promising was the suggestion of the botanist Andrea Cesalpino (1519-1603) of Padua and Pisa, who attempted to class plants according to their flowers and fruits. The scheme formed on this basis was by far the best of the kind that had yet appeared. A small part of it was absorbed into the influential work of Cas par Bauhin of Basle (1550-1624 q.v.). For the most part, how ever, it fell on sterile ground and was little noticed till the time of Linnaeus.
So far as general arrangement is concerned Bauhin was dis tinctly inferior to Cesalpino. He gives, however, descriptions of about 6,000 plants. The great merit of his book is that in it for the first time the species of plants are placed together in small definite groups or genera. The modern conception of genus and species is in fact Bauhin's more than that of anybody else, and he and not Linnaeus is the true introducer of the binomial nomenclature which since Linnaeus has been in universal use.
Important steps in the direction of a systematic arrangement of living things were made by the two friends John Ray (1627– 1705) and Francis Willughby (1635-72). They formed a scheme for a systematic description of the whole organic world. Wil lughby was to undertake the animals, Ray the plants. Willughby died early and in the event Ray became the chief founder of the science of systematic biology. His early attempts on the flora of Cambridge and his treatise on birds were followed in 1682 by his important New System of Plants. In this the true nature of buds and used the divisions of flowering plants into dicotyledons and monocotyledons. He based his system largely upon the fruit, but also upon the leaf and other charac teristics and especially, following Cesalpino, upon the flowers. In doing this he succeeded in disentangling a number of the larger groupings of plants now known as families. His work in botany was completed by his Synopsis of British Plants and followed up by a Synopsis of Quadrupeds and Serpents (1693) . This con tains the first truly systematic arrangement of animals. It is based upon the fingers and toes and teeth of the animals concerned.
The systematic study of living things begun by Bauhin and Ray was continued by the Swede, Linnaeus (1707-78), the great est of the systematists. Linnaeus brought to bear upon his life work an enormous acquaintance with living things, especially plants, gained in the field. His prodigious industry and power of systematic arrangement would alone have given him a high place among naturalists. He profited from all the best teachers of the day, visiting many parts of Europe, including Holland, France and England. He was a most inspiring teacher and had numerous pupils, one of whom accompanied the English explorer, Captain Cook, and was for many years resident in London. Linnaeus be came a sort of biological dictator, and for a century after his time most of the biological work that was done in every country was in his spirit.
Linnaeus had a perfect passion for classification and succeeded in assigning to every known animal and plant a position in his system. This involved placing any specimen first in a class, then in an order, then in a genus, then in a species. The broad out line of his system of classification has remained, though its rigid framework has long ago been abandoned.
The chief service of Linnaeus to biology is his method—derived from Bauhin, and impressed upon his contemporaries—of arrang ing living things into genera and species, with his development of the "binomial" system. His system extended even to man, and he distinguished Homo sapiens from Homo troglodytes. His Sys tema Naturae went into many editions, the most highly prized being the tenth, to which naturalists still refer when they speak of Linnaean genera and species.
Linnaeus held that species are constant and invariable, a view in which he differed from John Ray. He assumed that all the members of a species were descended from a single pair that had been originally created. He afterwards modified this view and came to hold that it was the genera, not the species, which had issued from the Godhead.
The Beginning of the Study of Comparative Anatomy and Physiology.—The first animal whose naked eye structure was adequately explored was man himself. The anatomy of man was placed upon a sound basis by Vesalius in his wonderful mono graph of 1543. For certain organs of the body Vesalius had not any adequate access to human material. Thus his account of the eye and of the organ of voice are taken from the dog. He was aware of differences in structure between man and animals and he chose several opportunities in his work to adopt a comparative method. A similar device is invoked by Pierre Belon. During the century several other observers made dissections of animals and compared them to man. None was more exact than Ruini, a lawyer of Bologna, who published his monograph on the horse in 1598.
As the 17th century advanced there were a number of workers who further extended comparative studies. Of these the classical microscopists were by far the most important ; for the most part they worked upon invertebrates. Monographs on various verte brates were also prepared, as for instance that on the chameleon by the Italian Francesco Redi, and that on the chimpanzee or "pygmy" by the Englishman Edward Tyson. Monographs on invertebrates were prepared by Malpighi on the silkworm, by Swammerdam on the mayfly, the bee and the snail, and by Leeu wenhoek on the development of the flea.
With the great movement initiated by the work of Harvey, something in the nature of comparative physiology became pos sible. Harvey's masterpiece is in fact in large part a comparative study of the circulation. Of comparative physiology there has never been a greater exponent than the English country parson, the Rev. Stephen Hales (1677-1761). Hales practically began the study of the functional activity of plants and his work was the most important in that department until the 19th century. He measured the amount of water taken in by the roots and given off by the leaves, comparing this with the amount of moisture in the earth and showing the relationship of the one to the other. He made calculations of the rate at which water rises in the stems, and he showed that this has a relation with the rate at which it enters by the roots and transpires through the leaves. He meas ured also the force of suction in wood and roots, that is to say, "root pressure." He sought to show that these actions of living plants might be explained as the result of their structure. His most important contribution for botanical physiology was perhaps his demonstration that the air contributes something to the build ing up of the substance of plants, and in this respect he may be said to have been the discoverer of carbon dioxide. Following this up, he showed that air enters the plant not only through leaves but also through the rind. His experiments and conclusions in the physiology of animals were as important as in that of plants. Here he showed that there is a pressure of the blood within the ves sels which can be measured, and that it varies in different cir cumstances and differs in the arteries and the veins. He even estimated the rate of flow in the capillaries. It is specially characteristic of his work that in all his experiments he sought to give a quantitative expression to his results. In this sense Hales was among the first to adopt exact methods in biology.
The comparative attitude in combination with exact experiment in biology was peculiarly characteristic of the investigators of the 18th century and separates them from those of the previous period. None pursued the method with greater enthusiasm than that great surgeon, John Hunter (1728-1793, q.v.; see also MEDI CINE, HISTORY OF). At the time of his death Hunter had anatom ized over 500 species of animals, many of them a great many times, as well as a great number of species of plants. The general object of his work might be described as a systematic attempt to trace the different phases of life as exhibited in the structure of animals and plants. Both in precept and example Hunter was the greatest influence in connection with the establishment of natural history museums, the subsequent development of which has followed lines very similar to those which he suggested.
Hitherto comparative studies had been the preoccupation of individual workers. Georges Cuvier (1769-1832), by means of his immensely powerful position, was able to establish a complete and organized school of comparative investigators which may be said to have continued to our own time. His influence was very stimulating to research, but it cannot be said that he invariably exerted his power with the greatest wisdom. He believed strongly in the fixity of species and thus opposed the views of Lamarck q.v.) and of Etienne Geoffroy Saint-Hilaire (1772 1844). Nevertheless by the palaeontological school which he founded and which extended into every country, he did perhaps more than any other man to collect material on which the doctrine of the impermanence of species became formally founded in later times.
Cuvier's great work, Le Regne Animale, has formed one of the main foundations for comparative studies even to our own time. Among the specific achievements of Cuvier was firstly the crea tion of the science of palaeontology, secondly the exploration of the anatomy of the group Mollusca, and thirdly his systematic treatment of the vast class of fishes. The tradition of Cuvier was carried to England by Richard Owen (1804-92), who afterwards became director of the British Museum of Natural History.
While Cuvier and his school led in the comparative study of structure, the comparative study of function which had been expounded by Hales was established on a firmer basis by the great German physiologist, Johannes Muller (1801-58). (See