Fibroin is insoluble in water, acids and alkalies; silk-glue resembles gelatin in its solubility, but it is less readily gelatinized.
Typical albuminoids are gelatin, keratin, elastin, fibroin, spongin and conchiolin.
"Fibroin " and silk-glue or sericin occur in natural silk fibres.
Silk fibre consists essentially of a centre or core of fibroin, with a covering of sericin or silk albumen, and a little waxy and colouring matter.
Fibroin, which is analogous to horn, hair and like dermal products, constitutes about 75 to 82% of the entire mass, and has a composition represented by the formula C15H23 506.
According to P. Bolley, the glands of the silkworm contain semi-liquid fibroin alone, and it is on exposure to the air that FIG.
All silk produced by the worm is composed of two substancesfibroin, the true thread, and sericin, which is a hard, gummy coating of the " fibroin."