Gossypium, B.P. Cotton.
Cotton (Gossypium Purificatum, U.S.P., Purified Cotton) consists of the hairs of the seeds of Gossypium barbadense,Linn. (N.O. Malvaceae), and other species of Gossypium. The plants are cultivated in tropical and sub-tropical countries. After removal from the seeds, the hairs are separated from impurities, and freed from fatty matter by boiling for half an hour with a 5 per cent. solution of potassium or sodium hydroxide. The cotton is then washed thoroughly with water, bleached by immersing in a 5 per cent. solution of chlorinated lime, again washed, and transferred to an acid bath. After further washing with water the bleached cotton is immersed in a weak alkaline bath for twenty minutes, again washed, dried, and the fibres mechanically loosened and separated in order to make a fleecy, absorbent "wool." Cotton occurs in soft, white filaments, from 2 to 5 centimetres long, each being a single hair from the seed. When examined under the microscope, the hairs appear as flattened twisted bands with slightly thickened edges. Cotton should be inodorous and tasteless, and readily absorb water, indicating absence of fatty matter, and should have neither an acid nor alkaline reaction.
Constituents.—Cotton consists chiefly of cellulose with traces of inorganic and protein matter. Prepared as described above, it absorbs water readily and is peculiarly suitable for the preparation of surgical dressings, the best variety for that purpose occurring in long, soft, white filaments. Derivatives of cellulose prepared from cotton are dinitrocellulose (pyroxylin) and trinitrocellulose (gun-cotton). The latter substance, one of the most powerful explosives, is not soluble in a mixture of alcohol and ether.
Uses.—Purified cotton is used largely as an absorbent or protective agent, and for applying various medicaments to the surface or cavities of the body. Used as a dressing to wounds, it takes up discharge, protects the part from external irritation and from cold, and excludes germs. For warmth, it is applied to the chest and back in sheets, and to gouty and rheumatic joints. The different kinds of medicated antiseptic cotton are much used in surgery as dressings for operation wounds. They are distinctively coloured to facilitate identification. Discharges usually bleach the colouring matter, and thus become obvious. Cotton is also used to plug the orifices of sterilised vessels, bacteriological culture tubes, etc. Absorbent gauze tissue, also known under the trade-name "Gamgee Tissue," consists of a thick layer of absorbent cotton, enclosed in absorbent gauze. It is used in large sheets as a protective, or absorbent of liquids (as in accouchement), or may be cut into pads and swabs of various sizes and shapes for use in surgery. A similar absorbent dressing is prepared from wood fibre; in loose pieces it is styled "Cellulose Wadding"; when prepared in sheets enclosed in absorbent gauze it is called "Cellulose Tissue."