YERSIN, ALEXANDRE EMILE JOHN ), Swiss bacteriologist, was born at Rougemont, Switzerland, on Sept. 2 2, 1863, and studied at Lausanne, Marburg and Paris. He was associated with Roux in his researches on the diphtheria serum at the Pasteur institute, and then continued his researches in China and Indo-China, where he explored the Mois country and pre pared a series of maps of the region. He introduced the culture of rubber into Indo-China. The plague bacillus was discovered by him in Hongkong in 1894, Kitasato simultaneously making the same discovery. The next year Yersin prepared a serum to combat the disease. Under the auspices of the Chinese Government a branch of the Pasteur institute was founded by him at Canton. Yersin established a similar institution at Nha Nang, Annam, in the same year, of which he became director. Yersin was awarded le grand prix Leconte by the Paris Academie des Sciences in 1927.
YEW (Taxes baccata), a tree which belongs to a genus of Coniferae (see GYMNOSPERMS), in which the ordinarily woody cone of the pines and spruces is represented by a single seed sur rounded by a fleshy berry-like cup. Usually it forms a low-grow ing evergreen tree of very diverse habit, but generally with dense spreading branches, thickly covered with very dark green linear leaves, which are given off from all sides of the branch, but which, owing to a twist in the base of the leaf, become arranged in a single series on each side of it.
The trees are usually dioecious, the male flowers being borne on one individual and the female on another. The male and the female flowers are placed each separately in the axil of a leaf, and consist of a number of overlapping scales. In the female flower these scales surround a cup which is at first shallow, green and thin (the so-called aril), but which subsequently becomes fleshy and red, while it increases so much in length as almost entirely to conceal the single straight seed. It is clear that the structure of the female flower differs from that of most conifers, from which it is now separated in a distinct family, Taxaceae.
The poisonous properties, referred to by classical writers such as Caesar, Virgil and Livy, reside chiefly if not entirely in the foliage. This, if eaten by horses or cattle, especially when it has been cut and thrown in heaps so as to undergo a process of fer mentation, is very injurious. As a timber tree the yew is used for cabinet-work and axle-trees, where strength and durability are required. It was once largely used for the English long-bow.
The European yew, T. baccata, is a native of Europe, north Africa, and Asia as far as the Himalayas and the Amur region. The yew is wild in Great Britain, forming a characteristic feature of the chalk downs of the southern counties and of the vegetation of parts of the Lake District and elsewhere. The evidence of fossil remains, antiquities and place-names indicates that it was formerly more widely spread in Europe than at the present day. The varie ties grown in the United Kingdom are numerous, one of the most striking being that known as the Irish yew—a shrub with the py ramidal or columnar habit of a cypress.
The yew is a favourite evergreen tree, either for planting sepa rately or for hedges, for which its dense foliage renders it well suited. Its dense growth when pruned has led to its extensive use in topiary work, which was introduced by John Evelyn and became very prevalent at about the beginning of the 18th century.
In the United States and Canada the best known native yews are the American yew or ground-hemlock (T. canadensis), a low, straggling shrub rarely over 5 ft. high, found in woods from New foundland to Manitoba and southward to Virginia and Iowa, and the western or Pacific yew (T. brevifolia), a tree sometimes 5o ft. high, with a trunk diameter of 2 ft., which grows from Cali fornia to Alaska and eastward to Montana. The hard, heavy, very fine-grained, exceedingly durable wood of the Pacific yew, one of the best woods used by the Indians for making bows, is especially suitable for tool-handles and similar purposes. Two other North American species occur: the Florida yew (T. flori dana), a rare tree of western Florida, and the Mexican yew (T. globosa), found in the mountains of Mexico.
Numerous dwarf forms and leaf-colour variants of the Japa nese yew (T. cuspidata), a tree sometimes 5o ft. high, native to north-eastern Asia, are planted for ornament.