evidence in favor of organic evolution together with a plausible explanation of the mechanism (natural selection) of its operation. To this we shall return. In a century so rich and so varied in its achievements in natural science as was the nineteenth, we can obviously only touch- and that very briefly and that very briefly — upon a few of the more important and fundamental.

Of the remarkable progress of all the sciences during the Victorian era, Huxley has given the best brief and general account in his essay entitled Advance of Science in the Last Half Century (1887), prepared in celebration of the first fifty years of the reign of Queen Victoria.

PROGRESS IN ZOOLOGY.-The work of Buffon and Linnæus in the field of biology and of Werner and Hutton and Smith in that of geology has been referred to in Chapter XIV. Of these only Werner (d. 1817) and Smith (d. 1839) lived on into the nineteenth century.

The return of the astronomers and the geologists to ancient ideas of gradual development or, as this is now called, evolution, for the lifeless earth, was foreshadowed for the living world with Bonnet (1720-1793) who in 1764, in his Contemplation de la nature, advanced the theory that living things form a gradual and natural "scale" (ladder), rising from lowest to highest without any break in continuity. Buffon, in his great work on natural history, which. was published between 1749-1804 in 44 quarto volumes, had Idealt with the animal world very much as Linnæus had dealt with plants, Buffon excelling in description, Linnæus both in description and in classification and holding firmly to the idea of the fixity as well as the definite demarcation of species.

Meantime, epoch-making work in zoölogy was being done by three investigators - Lamarck, Cuvier, and St. Hilaire — at the Museum of Natural History in Paris. In 1778 Lamarck (17441829) published a small book on botany. In 1801 appeared his great work On the Organization of Living Bodies, which is now a landmark in the history of biology and of the doctrine of organic evolution. In this work and in his Philosophie zoologique, Lamarck boldly proposes to substitute for special creation

the current theory of cosmogony - the idea of gradual development or evolution, an ancient idea thenceforward made the keynote of his speculations. Systematic zoölogy and comparative anatomy, the latter already well begun by Hunter in the ' eighteenth century, were immensely advanced by Cuvier (17691832), who however clung tenaciously to the theory of special creation; while Geoffroy St. Hilaire (1772-1844) also a comparative anatomist, but one whose interests lay rather in the functional than in the anatomical resemblances of the parts of animals, and who is therefore regarded as "the father of homology" on the whole opposed Cuvier's and favored Lamarck's ideas. His Philosophie anatomique appeared in 1818-1822.

Nature, said St. Hilaire, has formed all living beings on one plan, essentially the same in principle, but varied in a thousand ways in all the minor parts; all the differences are only a complication and modification of the same organs.

This similarity of structure, or homology as it is called, which runs through all animals, was thus first clearly stated by St. Hilaire, and has now been carefully worked out and confirmed. . Yet Cuvier opposed it to the last, for his mind was full of another idea which is equally true; namely, how perfectly each part of an animal is made to fit all the other parts; and it seemed to him impossible that this could be, unless each part was created expressly for the work it had to do.

The discussion between the two friends became so animated that all Europe was excited by it. It is said that Goethe, then an old man of eighty-one, meeting a friend, exclaimed, 'Well, what do you think of this great event? the volcano has burst forth, all is in flames.' His friend thought he spoke of the French Revolution of July, 1830, which had just occurred, and he answered accordingly. "You do not understand me,' said Goethe, 'I speak of the discussion between Cuvier and St. Hilaire: the matter is of the highest importance. The method of looking at nature which St. Hilaire has introduced can now never be lost sight of.' — Arabella Buckley Fisher.

The history of zoölogy in the first half of the nineteenth century is chiefly that of the work of Cuvier, St. Hilaire, Lamarck, Agassiz and their disciples.

PROGRESS IN BOTANY. - The Linnæan system of classification for the higher plants was a purely empirical system, based largely upon the number of stamens and not involving any ideas of relationship through descent. B. de Jussieu (1699–1767), a friend and pupil of Linnæus, had proposed a different system of classification in which weight is given to the totality of resemblances of whatever kind, and this, which almost inevitably led to the close association of related forms, was an important step toward a natural classification, i.e. one based avowedly upon relationship, common ancestry, or descent. De Jussieu's nephew Antoine de Jussieu continued and extended his uncle's work. A. de Candolle (1778-1841) later adopted and extended de Jussieu's system which, with his own, now forms the basis of our present natural system. It is noteworthy that this change of opinion in regard to the relationship of the species of plants was ultimately effected without theological protest.1

The discovery by Goethe of the homologies of the parts, and by Linnæus of the organs of sex, of the flower, were important steps toward the modern theory of the evolution of plant life.

PROGRESS IN MICROSCOPY. THE ACHROMATIC OBJECTIVE.— Compound microscopes, i.e. microscopes consisting of two lenses, an objective and an eyepiece, were probably invented at about the same time as telescopes, which likewise consist of two lenses or systems of lenses. But because of their imperfections, in respect especially to spherical and chromatic aberration, such microscopes were often inferior for use to the best simple microscopes. It was not until about 1835 that the compound microscope, though invented in the seventeenth century, became the superior instrument that it is to-day, through the accumulated improvements of a number of workers, — especially Amici, Lilly, Lister, and Chevalier — resulting in the achromatic objective, free from both spherical and chromatic aberration.

Almost immediately thereafter, with the new microscopy, began a rich harvest of discoveries, in what Pasteur has called the

1 For an account of Linnæus' attitude to the doctrine of the fixity of species see A. D. White, Warfare of Science, Vol. I, pp. 47, 59, 60.

world of the infinitely little, similar to that reaped after the introduction of the telescope by Galileo, and his exploration of the stars, in the world of the infinitely great. The cell theory of Schleiden and Schwann appeared in 1839 and yeast was rediscovered (see p. 378) in 1837. The first contagious disease (Muscardine) traced to a fungus parasite was worked out by Bassi in 1837, the first contagious disease (Favus) of man due to a fungus, by Schoenlein in 1839. Protoplasm was first described in 1846. Ehrenberg, in 1838, made numerous and important studies on microscopic plants and animals.

EMBRYOLOGY. —If in 1828 one sharp boundary which had always been supposed to stand between the organic and the inorganic world was broken down by Wöhler's discovery that urea, a substance hitherto exclusively of animal origin, could be obtained in the laboratory by heating an inorganic substance, ammonium cyanate, another well-defined boundary believed to exist between the higher and the lower animals had been broken down a year earlier, when a Russian zoölogist, Karl Ernst von Baer (1792-1876), announced that mammals, including man himself, reproduce by eggs, precisely as do the lower animals. In 1828 von Baer published our first important work on comparative embryology, — of which science he thus became the founder.

The discovery by von Baer of the human ovum overthrew completely the "animalculists" who for centuries had contended that within the earliest embryo of man the future offspring existed completely formed, but only in miniature. This theory, because it assumed for development a mere unfolding, was known as embryologic evolution. Harvey, on the other hand, had propounded a theory of epigenesis, i.e. development comprising growth and differentiation out of an originally minute, simple, and undifferentiated body. This "body"- the human ovum - was now described by von Baer as inch in diameter and nowise different in appearance from other animal eggs in their earliest stages. Comparative anatomy had already shown that Linnæus was right in placing man among the animals, and now embryology confirmed and strengthened this view of man's place in nature.

PROGRESS IN PHYSIOLOGY. JOHANNES MÜLLER. CLAUDE BERNARD. To the work upon physiology of Harvey in the seventeenth century and of Haller and Bichat and others in the eighteenth was now added that of Johannes Müller (1801-1858) whose "Elements of Physiology," appearing between 1837 and 1840, put the whole subject on a fresh and thoroughly scientific basis. Müller has been called the founder of modern physiology. Fortunate in his pupils - DuBois Reymond, Helmholtz, Ludwig, Volkmann, and Vierordt these were no less fortunate in their master, for Müller was a great teacher, and for the rest of the century the teachings of Johannes Müller and his disciples furnished a powerful stimulus and a safe guide to physiological research, especially in Germany.

In France, also, physiology won renown and recognition through the researches of Claude Bernard (1813-1878), a pupil of Magendie, whose assistant he became in 1841 and whom he succeeded as assistant professor in 1847 and as professor in 1855. Bernard was the first occupant of the newly established chair of physiology at the Sorbonne. The laboratory was attached to his professorship until 1864. On his death in 1878 he was accorded by the State the honor of a public funeral, the first ever bestowed by France upon a man of science and only 84 years after the public guillotining of Lavoisier. By his discovery of the significance of the pancreatic secretion and especially of the glycogenic function of the liver Bernard opened up the vast field of "internal secretions," the study of which has yielded, and is still yielding, some of the most fruitful results of physiological research hitherto obtained. Before Bernard, each organ seemed to have one function and only one, but since his time this simple, mechanical concept has given way to a realization of correlations and complexities within the animal mechanism such as had not then been dreamt of.

A great step forward in this dark field was taken in 1843 by the French physiologist, Claude Bernard, a man whose name should be remembered for his striking discoveries, ingenious and skillful experiments, his clear thoughts, lofty imagination and the beautiful,