The career of Pasteur exhibits a striking unity. His first research, which dealt with a subject so remote from the ordinary studies of the biologist as the crystalline forms of tartrates, made him acquainted with activities, hitherto unsuspected, of minute forms of life. The hope of aiding the industries of Lille, Orleans, and France kept him long engaged upon ferments. If he turned aside to examine the superstition of spontaneous generation, it was to protect his methods from misconstruction. An apparent break in his programme of work was forced upon him by the silkworm pestilence. It proved to be no real break, for pébrine and flacherie were both bacterial diseases. At a comparatively early date (1863) he wrote that his chief ambition was to throw light on the spread of contagious diseases; he could not then foresee that he was destined, not only to elucidate, but in a measure to control them. Around his tomb are inscribed words, each of which commemorates a signal service to his fellow-men: "1848, Molecular dissymetry. 1857, Fermentations. 1862, Spontaneous generation. 1863, Studies of wine. 1865, Silkworm diseases. 1871, Studies on beer. 1877, Contagious diseases of animals. 1880, Vaccination against contagious diseases. 1885, Prevention of hydrophobia." These manifold researches form a continuous chain, each being linked to what precedes and follows. The devotion by which all were inspired, beginning with devotion to science and the fatherland, ended by embracing all mankind. * * * * * Biology, which in the sixteenth century sent out only a few feeble shoots, has now become a mighty tree with innumerable fruit-laden branches. The vigour of its latest outgrowths encourages confident hopes of future expansion. [44] Titius of Wittenberg, who published in 1766 what is commonly called Bode's law of planetary distances, objected to the Linnean system on the ground that it multiplied the principle of division. (_De divisione animalium generali_, 1760.) [45] _Origin of Species_, chap. xiii. [46] _Geol. Survey Memoirs_, 1846. [47] By a curious and no doubt accidental coincidence, Darwin employs the same remarkable metaphor which had occurred to Iordanes in the sixth century A.D. Iordanes calls the north the _officina gentium_. [48] Introduction to _Entomology_, Introductory Letter. [49] _Life and Letters_, Vol. I., chap. ii. [50] Darwin, _Variation of Plants and Animals under Domestication_, Concluding Remarks. CHRONOLOGICAL TABLE 1200-1850 (The date of a discovery is the date of first publication, where this is known.) 1202. Arabic numeration introduced into Europe by Leonardo of Pisa (Liber Abaci); it spread slowly, and did not become universal till the middle of the seventeenth century. 1214-1294. Roger Bacon. 1265-1321. Dante. 1271-1295. Travels of Marco Polo. 1304~1374. Petrarch. 1324?-1384. Wycliffe.