730 Chemistry: Boyle. Van Helmont. Sylvius woven with the progress of Chemistry that it will be better to consider the two together. During the latter part of the sixteenth and earlier part of the seventeenth century, though the day of alchemy was past, there was great activity in the preparation of new chemical substances: this was due partly to natural curiosity, partly to the demand for new remedies and for new industrial materials. And these preparations were conducted to a very large extent by the method of exact measurement which in Physics was proving so fruitful. But there was no corresponding progress in chemical theory; "chemists," said Boyle, "have been much more happy in finding experiments than the causes of them, or in assigning the principles by which they may best be explained." Chemists continued to accept the three "elements" or "principles " of Paracelsus, or rather of Valentine, namely, sulphur, mercury, and salt that is to say, the classification of substances into those which were combustible and were lost by combustion, those which were volatile and recovered after combustion, and those which remained after combustion. Nicolas Lefèvre (d. 1674) and others, it is true, speaking of "oil" instead of sulphur, of "spirit" instead of mercury, added to the three active two passive principles -"water" or "phlegm " and " earth "; but this implied no great change. - Later in the seventeenth century, Boyle laid the foundations of modern Chemistry by severely criticising in his Sceptical Chemist (1661) those "principles " or " elements," and propounding the pregnant idea, that all matter was made up of minute "corpuscles" capable of arranging themselves in groups, small and simple, or large and complex; that each such group constituted a chemical substance; and that chemical change was a rearrangement of groups, a chemical compound being a union of the constituents and capable of differing in qualities from either of them; and he attained to far-seeing views as to the part played by heat in determining the arrangement of the corpuscles. But his conceptions were slow in making way. Two other men had a much more immediate effect on the chemical learning of the century. Jean-Baptiste van Helmont (1577-1644), in whom the exact quantitative observer and experimentalist was strangely joined to the visionary, besides discovering many new chemical substances, laid hold of some important truths. He introduced the idea of "gas "as something distinct from either air or vapour, and recognised as gas sylvestre what we now know as carbonic acid gas. He developed in detail a doctrine of fermentations, and applied it to Physiology. His description of the chemical processes of the living body as a series of six "fermentative concoctions," by which the dead food is converted into blood, first venous, then arterial, and subsequently into the living active tissues though marred by his spiritualistic ideas and his ignoring all that Harvey had done contains much that is interesting. A very different man was Francis Sylvius (de La Boé) (1614-72), a zealous exponent of Harvey's teaching, and of all the new views in The iatro-chemical and iatro-physical schools 731 Physiology and in Physics, who, while vigorously endeavouring to extend purely chemical knowledge (he was the first to have a Laboratorium), strove also to apply it to the problems of living beings and so became at the same time the great teacher of the day in both Chemistry and Medicine. Taking up the work of Johann Rudolf Glauber (1603–68), who in discovering his sal mirabile, sodium sulphate, since and even still known as "Glauber's salt," had considered it to be a compound of an acid with an alkali; and, assisted by the labours of his pupil Otto Tachenius (d. 1670 c.), who even more clearly recognised that all salts were similarly compounds of acids and bases, and who thus gained a general conception of chemical affinity, Sylvius drew the distinction between. acidum and lixivium or alkalinum-the basis of a classification of chemical substances; he strove, indeed, to explain many if not all chemical phenomena, both in the living body and elsewhere, as the results of the actions of acids and alkalis. The bubbles rising up in the fermenting vat were according to him brought about in the same way as the bubbles which came when oil of vitriol was thrown upon chalk; fermentation was to him the same thing as effervescence. He used the two terms indifferently and strove to explain, not only digestion in which the discoveries of Stensen, Wharton, and his own pupil Regnier de Graaf (1641-73), led him to attach great importance to saliva and pancreatic juice, the one in his view being alkaline, the other acid, but most of the changes in the body as a series of" effervescences," aided by " precipitations." Nowhere did he find need to appeal to any spiritualistic forces; chemical action was adequate to explain all the phenomena of the living body; and the chemical actions met with there he regarded as identical with the chemical actions seen in the beakers and retorts of the laboratory. Thus he became the chief exponent of what was called the "iatro-chemical" school. Meanwhile, Borelli was in like manner explaining everything from a mechanical-physical standpoint, teaching, for instance, that digestion in the stomach was a mere mechanical crushing of the food by muscular action into minutest fragments, and that secretion was a sifting through the sieve of the secreting organ of particles whose size and shape allowed them to pass through adaptive minute pores. Thus he in turn became the founder of the "iatro-physical" school. Both schools did much, and the English school previously mentioned perhaps even more, to advance knowledge; but the close of the century witnessed a remarkable development of chemical conceptions, which turned biological doctrines aside from the line which they had seemed to be taking. The exact part played by heat or fire in chemical actions had from quite early times been the subject of great discussion, Boyle (as we have seen) having had much to say about it; and now a wholly new notion was started. Johann Joachim Becher (1635-82) in attempting to revive Valentine's old "elements" in the form that all things consisted of three earths, "terra lapidea, improperly called salt, terra fluida, 732 The phlogiston theory improperly called mercury, and terra pinguis, improperly called sulphur," maintained that, when a substance was burnt, the terra pinguis previously contained in it escaped; indeed that this escape of terra pinguis was the essential feature of combustion. Taking up this idea, George Ernest Stahl (1660-1734) developed it more fully into what became known as the phlogiston theory. By phlogiston Stahl meant, not fire itself, but "the material and principle of fire"; and this he regarded as a material substance working in the following way. Everything which can burn does so by virtue of its holding phlogiston, and the act of burning is the giving out or loss of it. That which holds no phlogiston cannot of itself burn; but it may support combustion by taking in the phlogiston given out by the burning body. Thus, air which is to a large extent free from phlogiston is a great supporter of combustion; and many other things also free from it can bring about combustion. The phlogiston theory was so powerfully advocated and proved so attractive that though it argued burning to be a loss, and though it was thus in direct contradiction to the teaching of Boyle and Mayowwho showed that certain things, metals for instance, increased in weight by burning the theory not only gained immediate and general acceptance, but also remained dominant during the whole of the century. Stahl by his phlogiston theory not only profoundly influenced Chemistry and thus indirectly Physiology, but also exercised a most powerful effect on all biological enquiry by his earnest advocacy of spiritualistic conceptions. He put forward and brilliantly maintained the conception that all the chemical events of the living body, even though they might superficially resemble them, were at the bottom wholly different from the chemical changes taking place in the laboratory, since in the living body all chemical changes were directly governed by the sensitive soul (anima sensitiva) which pervaded all parts and presided over all events. The pendulum swung back from the somewhat crude materialism of Sylvius; in the views of the eighteenth century Stahl's "sensitive soul" was dominant, and under the weaker title of "vital force " is powerful even at the present day. In the seventeenth century some at least of the modern doctrines of the nervous system began also to take shape. In the Galenic teaching the "animal spirits" were concocted in the ventricles of the brain by a mingling of the vital spirits, brought by the arterial blood, with air drawn in directly from without through the pores of the ethmoid bone. Within the several ventricles these animal spirits carried out the various func tions of the soul, which they supplied with sensations by flowing upwards along the nerves. Flowing downward along the nerves, they entered the fibres, the tendinous part of a muscle, and, by swelling these up, brought about enlargement or contraction of the muscle, the fleshy part of which played a wholly passive part, and so gave rise to movement. Nicolaus Stensen was the first to show, in 1664, that the fleshy part of the muscle-the fleshy fibres, and not the tendinous part-was the active contracting part, the contraction of the whole muscle being the result of the contraction of the individual fibres; and he came very near to quite recent views of the essential nature of muscular contraction. Borelli, profiting by Stensen's discoveries and applying to the subject his exact Mechanics and Physics, brought, at one stride as it were, the knowledge of muscular mechanics almost up to the knowledge of to-day. On one point he failed to free himself from the old Galenic views; he maintained that contraction was essentially an inflation, an increase in bulk. The nerves in his view were occupied not by animal spirits, but by a fluid, the succus nerveus, a "highly subtle and spirituous," yet still a strictly physical, fluid, incapable of acting at a distance. Sensation and movement were, according to him, brought about not by this succus flowing to and fro, but by means of "concussions" passing along it. He admitted that the mere advent of a concussion to the substance of a muscle could not of itself cause an inflation and contraction; he supposed that it excited in the muscle some change possibly of a "fermentative," that is to say, of a chemical, nature. An important advance was made by Francis Glisson (1597-1677), who on the one hand introduced the idea and the word "irritability," as applied to muscular and other tissues, to denote the faculty of being irritated a conception destined to play so important a part in physi ology and pathology, and on the other hand made and described the experiment which still remains as a classic lecture experiment, that a muscle in contracting does not displace water, showing that contraction is a change of form only, not of bulk. In this experiment the old Galenic teaching received its last and fatal blow. While this remarkable progress was taking place in the so to speak lower regions of Nervous Physiology, there was no corresponding advance in the higher regions. Solid additions to our knowledge of the anatomy, of the brain were, it is true, furnished by Thomas Willis (1621), the ~ (1621-75) chief merit of whose work rumours of the time however attributed to Richard Lower, who assisted him in it; but, when we turn to the functions of the brain, we find nothing much beyond fanciful speculations. Descartes, ignoring Harvey's work and making use of the old Galenic doctrines, expounded the body of man, including the nervous system, as a machine capable of being explained by the new mechanical-physical learning with the help of various assumptions, as, for instance, that the nerves were tubes along which the flow of animal spirits was regulated by valves; this body however, though capable of doing much by itself, especially by what we now call reflex actions, was governed by the "rational soul" hovering around the pineal gland. Van Helmont taught the existence of an anima sensitiva motivaque, which, though residing in the pylorus of the stomach, carried out by means of the brain and nervous system the psychical work as well as the sensations and movements of 734 Higher Nervous Physiology. Botany the body; this soul however was mortal, though it contained within itself, after the fashion of a kernel, the "immortal mind." Stahl, as we have seen, carried on van Helmont's idea of anima sensitiva, though stripped of its fanciful wrappings. And Willis, though his experience as a physician led him to associate the corpora striata with movement and sensation, and the optic thalami with vision, both however acting as instruments of the higher cortex, revelled in conceptions at least as fanciful as those just mentioned. He likened the vital spirits in the blood to flame, and the animal spirits in the nervous system to light; and, while he explained all the actions of the nervous system as the functions of a corporeal and mortal soul present in brutes no less than in man, he claimed for man the possession also of a rational immortal soul, which performed all the higher psychical functions. About all these higher functions of the nervous system and the nature of the soul the exact observers Malpighi, Borelli, Lower, Sylvius and the rest were silent. Only one of these spoke on the subject, and then with a few words, mostly negative. In a lecture delivered at Paris on the anatomy of the brain (1669), Stensen, after criticising severely the views of Descartes and of Willis, on the ground that it is impossible to explain the movements of a machine, so long as we remain ignorant of the structure of its parts, and after explaining the great difficulties met with in studying the structure of the brain, anticipated modern discoveries by the suggestion that its fibres were arranged "according to some definite pattern, on which doubtless depends the diversity of sensations and movements.' Partly owing to the use of herbs as remedies, partly to natural curiosity and the love of beautiful flowers, the sixteenth century was very active in the recognition and description of plants. From the middle of the century onwards Botanic Gardens were established at Padua, Pisa, Bologna, Leyden, and elsewhere; and during the latter half of the sixteenth and beginning of the seventeenth century a number of elaborate, sometimes highly illustrated descriptions of plants, often known as "herbals," were published by men, many of whose names are in common use as names of plants, such as Fuchs, Gesner, Dodoens, de L'Écluse (Clusius), de L'Obel (Lobelius), and Bauhin. These descrip tions naturally implied a study of the organs of plants, and various methods of naming them, as well as attempts at classification. The most important, perhaps, and one of the earliest of such classifications was that by Caesalpinus (1583), drawn up however more from an à priori philosophical than from a direct natural history point of view. A classi fication introduced later by Joachim Jung (1587-1657) published after his death in 1678, as well as one by Robert Morison (1620-83), appear to have been used. John Ray (1628-1705), who in his Historia Plantarum, published between 1686 and 1704, proposed an arrangement |