With regard to the consumption, it was estimated that in 1907 Europe used some twenty-five million pounds, and the United States fifteen million pounds of raw silk, which, at an average price of nearly $5.50 per pound, amounted to over two hundred and eighteen million dollars. =Origin and Varieties of Silk.=—Silk has been defined as a “smooth, lustrous, elastic fibre of small diameter and of animal origin.” As is well known, ordinary commercial silk is secreted or “spun” by the silkworm, the caterpillar form of a moth known as _Bombyx Mori_, the moth of the mulberry tree. These silkworms have been cultivated for thousands of years, but there exist in different parts of the world, notably in India and Japan, wild or uncultivated silkworms, derived from nearly related, but not identical, families of moths, and whose silk is collected in the forests by the natives, forming what is known in commerce as wild or tussah silk. Of course, the silk from silkworms, cultivated and wild, is the only one yet produced on a commercial scale. But silk can also be obtained from other animals, notably from spiders and from a peculiar shellfish, the pinna, found in the waters of the Mediterranean. Silk from the silkworm can be divided into two classes, according to whether the silkworms are the cultivated or the wild varieties. In each case the silk is produced by the caterpillar spinning a covering or shroud, the so-called cocoon, around itself to protect it when in the form of the chrysalis or pupa, awaiting its transformation into the moth. The ordinary or cultivated silk of commerce comes from worms fed almost exclusively upon the leaves of the white mulberry tree, and cannot be produced successfully without that particular plant. The somewhat similar worms that produce the wild or tussah silks live upon the leaves of the oak, elm, ailanthus, castor oil plant, and others. While the two varieties resemble each other greatly in their chemical properties, they can always be distinguished, because cultivated silk is much more lustrous than the other, but is decidedly less strong. _Tussah Silk, Pongee, Shantung._—The tussah silks, when woven, are commonly known under the general name of pongee. Of late years this name has been applied to imitation goods possessing the characteristic dull color, and even the feel of the real article, but far less strong. These are generally made out of spun silk, derived from “Shappe,” i.e., the by-products of the silk industry, spoilt cocoons, waste from the spinning machines and the dyehouses, and the like—silk, to be sure, but silk of very inferior quality. Accordingly, it is now customary to call real pongee by the name Shantung, after the Chinese province from which much of the wild silk is brought.