Cocoons to be used for silk manufacture must be submitted to heat soon after they are completed, in order to kill the chrysalis and prevent it from forcing its way out, thus breaking the fibres. A certain proportion of the cocoons of each crop, however, is allowed to go through the natural process, for reproductive purposes. There is an active market in these breeding cocoons, particularly in Japan and China, and a large quantity are exported annually to Europe and the Near East. [Sidenote: _Construction of the Silk Thread_] The female cocoon is oval and the male cocoon is peanut shaped. The silk itself consists of two parts: fibroin (the silk fibre) and sericin (the gum). The thread is made up of two strands of fibre held together by the gum, and the length of thread in a single cocoon varies from three hundred to fourteen hundred yards. The cocoons are white, yellowish, or greenish, but after the boiling process the color of the _Bombyx mori_ silk is pure white. [Illustration: _Japanese Cocoon Market_] [Sidenote: _Tussah and Wild Silk_] The preceding description is concerned more particularly with the latter type, from which the largest proportion of the world’s silk supply is derived, but in a general way it applies to the other types also. The most important of these are the Tussah silk of India and China and the Japanese wild silk. The products are coarser and harsher than those of the _Bombyx mori_, and the natural color is brown. [Illustration: _A Japanese Filature_] CHAPTER II REELING 1. HISTORY OF THE FILATURE [Sidenote: _Early Reeling and Twisting_] [Sidenote: _Vaucanson’s Filature_] [Sidenote: _Silk Manufacture in Europe_]