plants breathe through the little stomata, or mouths, discovered by Grew (see p. 141). From the juices of plants Boerhaave next went on to those of animals, and he decomposed in a most beautiful and simple manner milk, blood, bile, and those fluids called chyle and lymph which convey nourishment to the blood. These he compared with the sap, gums, resins, and oils of plants, and showed that animal bodies are made up of altered vegetable matter, just as plants are in their turn composed of matter taken from the soil and the air; and he suggested that by careful experiments it would at last be possible to discover exactly the materials of which all living beings were made. Yet Boerhaave's analyses of organic substances were very rough and imperfect compared to those which are made now; for you must remember that the four gases, oxygen, hydrogen, nitrogen, and carbonic acid, which we now know are the chief constituents of plants, were not yet discovered. even these rough attempts were so interesting that students crowded round the doors of his lecture-room for hours before the lecture began, to secure admission; and there can be no doubt that his 'Elements of Chemistry,' published in 1732, contained the first steps in the study of the chemistry of living things. Boerhaave was also a celebrated botanist. He died in 1738, and deserves always to be remembered as one of the greatest teachers of the eighteenth century. Chief Works consulted.—Brewster's 'Encyclopædia ’—‘Boerhaave;' Cuvier, 'Hist. des Sciences Naturelles ;' Sprengel, 'Hist. de la Médicine,' 1815; Burton's 'Life and Writings of Boerhaave,' 1746; Boerhaave, Elements of Chemistry,' Englished by Dallowe, 1735; Miller's 'Chemistry; Hales' 'Essays concerning Vegetable Staticks,' 1759. ་ CH. XXIV. HALLER-ANATOMIST. 195 CHAPTER XXIV. SCIENCE OF THE EIGHTEENTH CENTURY (CONTINued). Childhood of Haller-Foundation of the University of Göttingen in 1736-Haller made Professor of Anatomy-Haller's Anatomical Plates-He discovers the power of Contraction of the MusclesRise of Comparative Anatomy-John Hunter's industry in Dissecting and comparing the Structures of different Animals - His Museum and the arrangement of his Collection--Bonnet's Experiments on Plants — Experiments upon Animals by Bonnet and Spallanzani-Regrowth of different parts when cut off-Bonnet's theory of Gradual Development of Plants and Animals-Anatomical Works of Haller-He discovers the power of the Muscles to con tract. - Haller, 1708–1777.-Among the pupils of Boerhaave there was one man who became, if possible, even more famous than his master. This was Albert von Haller, son of the Chancellor of Baden, who was born at Berne in 1708, and died in 1777. Haller seems to have been a most extraordinary child; at nine years of age it is said that he knew Latin and Greek, had made a Hebrew and Greek dictionary, a Chaldean grammar, and an historical dictionary! We are not told how good these books were; but how very few boys of nine years old would have been able to write them at all! At seventeen Haller went to Leyden to study under Boerhaave, and under Albinus, a famous anatomist; and at nineteen he was already a doctor of medicine. Having been driven out of Paris because the people were horrified at his dissecting dead bodies, he went to Berne, where he became professor of anatomy; and in 1736, when George II. of England, who was also Elector of Hanover, founded the University of Göttingen, he went there as professor of anatomy, surgery, and botany, and soon made that University as famous as Boerhaave had made Leyden. One of his first reforms was to turn the work of his pupils to good account. When medical students are going to pass their last examination they are required to write an essay, or thesis, as it is called, before they can receive their degree of doctor. Haller used always at these times to propose to each one of his students some difficult point in anatomy or physiology, in which he thought new discoveries might be made, and he then drew out a plan for them and showed them how to begin. By this means their essays were often full of new and useful information, and it was a great deal owing to the help of his pupils that Haller was able to publish 180 volumes on science, all more or less valuable. There was also a very good anatomical theatre at Göttingen, and from dissections made there Haller produced a set of most beautiful anatomical drawings, which he published between 1743 and 1753. You will remember that Vesalius published many fine engravings of parts of the human body (see p. 67), and since his time many others had been made, especially by Haller's master, Albinus. But Vesalius' drawings were coarse, because he had no microscope to help him, and Albinus had only drawn separate parts, such as a muscle, a nerve, or a vein. Haller's plates were the first which showed the different nerves and vessels attached in their right position, and to each plate he added a complete history of the function, or use of the parts drawn. He made these drawings so accurate, and spent so CH. XXIV. COMPARATIVE ANATOMY. 197 much time upon each minute structure, that in seventeen years, with all the help he had, he was not able to complete the description of the whole human body. Haller discovers the Power of the Muscles to Contract. -It was while he was at work at these dissections that he made one great discovery, which you must try to understand. If you clasp your right hand round your left arm, just above the elbow, and then bend your left arm, you will feel the part under your hand swell up and grow hard. The reason of this is that the muscle of your arm, called the biceps, has contracted, or grown shorter and thicker, in the process of bending your arm. If you open your arm again, the swelling will go down, because the muscle is stretched out. Now before Haller's time it was thought that the muscles could not contract of themselves, but were drawn up by the Haller discovered that this is not so, but that a muscle, if irritated, will draw itself together even when it is quite separated from the nerves, and this has since been proved to be true by a great number of experiments. So that though it is true that our nerves are the cause of our moving, because they excite the muscles and so make them contract, yet the real power of contraction is in the muscle itself. nerves. Comparative Anatomy, or the Comparison of Different Structures in Men and Animals.-John Hunter.-Another point in which Haller did good service to science was in comparing the same parts of the body of men and animals, and showing how far they are alike. This study, which is called the study of comparative anatomy, has now become very important, for by examining any organ, such as the heart for example, from the lower animals in which it is very simple, up to man in whom it is complicated, we can trace its gradual improvement, and understand it much more perfectly. Aristotle and Vesalius had both of them compared some of the parts of different animals, and so had other and later zoologists; but Haller was the first to make it a regular study, and John Hunter, who lived about the same time, devoted his whole life to it, and raised it to the rank of a separate science. John Hunter, who was born in the County of Lanark, in 1728, was the brother of a very eminent London physician, Dr. William Hunter, who was also a great anatomist. John, being delicate, had been allowed to grow up with very little education, and at twenty years of age he came up to London, a mere ignorant lad, to try and help his brother in his anatomical dissections. Here he soon showed that he had plenty of ability, for he learnt dissecting so rapidly that at the end of a year he was able to teach his brother's pupils, and before long he became one of the leading surgeons at St. George's Hospital, and had a large private practice. But though he made a great deal of money by his profession, he spent it all upon his favourite study of anatomy, to which he devoted every spare moment. His great wish was to compare thoroughly the different parts of men and animals, so as to show how the life of each one of them is carried on. For this purpose he dissected and preserved in different ways the bodies of all the animals he could lay his hands upon. He bought up all the wild beasts that died in the Tower, where they were then kept, and any which he could procure from travelling menageries, and he even kept foreign animals himself in a piece of ground at Earl's Court, Brompton, that he might watch their habits and dissect their dead bodies. As years went on and his specimens increased he built a |