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.