With the subsequent decline of the Roman Empire, a long period of scientific inactivity, or perhaps rather retrogression, took place. The Arabian Empire then rose, and seats of learning were established and encouraged at Bagdad, Cordova, Toledo, etc. The Arabians acted chiefly as the transmitters of Greek and Roman knowledge, adding comparatively little of their own. The most important of their writers were Geber, Rhazes, Avicenna, and Ibn Baitar.

Geber (a.d. 850 ?), who studied at Cordova, wrote chiefly concerning salts of which a considerable number were known to him.

Rhazes (a.d. 875 ?) studied medicine in Bagdad, and with him a period of independent investigation began. He was acquainted with asafetida, aloes, dandelion, henbane, stavesacre, and numerous other drugs; he prepared extracts by evaporating infusions and made them into pills, which he coated with psyllium mucilage in order to render them less unpleasant to take.

Avicenna (a.d. 980) was perhaps the most gifted of the Arabian physicians and a very prolific writer. His ' Canon Medicinae ' served as the chief source of medical knowledge down to the fifteenth century.

Ibn Baitar (a.d. 1197-1248) devoted himself chiefly to botanical work in which he excelled, his ' Corpus Simplicium Medicamentorum,' containing descriptions of about 2,000 drugs, of which 1,700 were of vegetable origin.

The Arabian school was followed by that of Salerno, near Naples, where a school of medicine, established in the twelfth century or possibly earlier, was instrumental in continuing scientific work until the dawn of science in Europe in the fifteenth century. During this period the knowledge at least of indigenous medicinal plants was kept alive and added to in the gardens attached to the convents and monasteries of Central Europe.

The beginning of the sixteenth century witnessed a revival in the study of drugs, which was stimulated by the discovery of America, of the West Indies, and of the sea route to India. Matthiolus (1501-1577), who studied in Italy, published a commentary on Dioscorides, which enjoyed a great reputation; he also collected and dried plants for pharmacognostical purposes and prepared careful illustrations. Monardes (1493-1578) collected drugs and other products brought from America, forming thus what was probably the first museum of materia medica. Clusius (1526-1609) also collected drugs from drug merchants and examined them; his ' Rarium Plantarum Historia ' (1601) contains no fewer than 1,146 illustrations, many of which are of great excellence.

After the lapse of a considerable time, during which little of note was published, Pomet wrote his excellent and well-illustrated ' Histoire Generale des Drogues' (Paris, 1694), which was closely followed by Lemery's ' Traite Universel des Drogues Simples ' (Paris, 1697) and ' Dictionnaire des Drogues Simples' (4th ed., Paris, 1727), and later by Geoffroy's ' Tractatus de Materia Medica ' (Paris, 1741).

The period of modern pharmacognosy may be said to open with Guibourt's admirable ' Histoire Abregee des Drogues Simples' (Paris, 1820), of which several editions were published. Guibourt relied largely on his own observations, and treated the subject from a purely pharmacognostical point of view. This was not the case with Pereira, whose classical ' Elements of Materia Medica and Therapeutics' (London, 1839) embraced, as its title indicates, both pharmacognosy and therapeutics. Schleiden was the first to employ the microscope to distinguish drugs by differences in their structure, a departure which was rapidly advanced by Berg and Schmidt ('Anatomischer Atlas,' Berlin, 1865), Vogl, and Moeller. Hanbury studied chiefly the botany aud commerce of drugs, while Fluckiger devoted himself chiefly to the chemistry and history, the collaboration of these two celebrated pharmacognosists resulting in the publication of the classical ' Pharmacographia ' (London, 1874). Meyer (' Wissen-schaftliche Droguen-Kunde,' Berlin, 1891) followed the.morphological development of drugs, Tschirch (' Anatomischer Atlas,' Leipzig, 1900) their structural development, and E. M. Holmes their botanical origin.

By these and other workers a mass of material has been accumulated, the systematical arrangement of which has been attempted by Tschirch in his 'Handbuch der Pharmakognosie.'

Commerce

The oldest records of commercial intercourse between different peoples indicate that several thousand years before the

Christian era a considerable trade existed in ancient Bactria, the modern Bokhara. At a very early period the Bactrians had undoubtedly made considerable progress in civilisation. The country was extremely fertile, and its position rendered it a convenient centre for the caravans that brought the spices and other products of India and China to Persia and Egypt. From Attock, near Peshawar, in the extreme north-west of India, caravan tracks led through Kabul to Bactria, and from China a northerly track had the same objective. From Attock similar routes passed through Assyria to the Black Sea, through Syria to the Mediterranean, and through Palestine to Egypt. During this period commerce was carried on almost entirely by caravans, the courses of the various routes being determined partly by the physical nature of the country to be traversed and partly by the presence of populous cities at which intermediate markets might be found; thus the routes from Bactria to Syria passed through Herat, Ecbatana, Nineveh, Babylon, and Palmyra.

During the rise of the Babylonian Empire (2000-1000 B.C.), at the time therefore at which the papyrus of Ebers was written, a considerable commerce existed between India, China, Syria (and the countries bordering on and even beyond the Mediterranean), and Egypt. In this commerce Arabia, favoured by its situation, took a very considerable part. Boats and rafts were used for descending the rivers, beasts of burden carrying the exchange back. Coasting vessels navigated the Persian Gulf, the Bed Sea, and the coasts of Arabia and India. Probably it was by one of these routes that cassia and other spices travelled from China to Egypt, and frankincense from Somaliland.