Every chemist knows that cotton is chiefly composed of cellulose, C_{6}H_{10}O_{5}, with some other substances in smaller quantities. This, although the usual opinion, is only true in a partial sense, as the author found on investigating samples of cotton from various sources. Thus, while mere cellulose contains carbon 44.44 per cent. and hydrogen 6.173, he found in Surat cotton 7.6 per cent. of hydrogen, in American cotton 6.3 per cent., and in Egyptian cotton 7.2 per cent. The fact is that along with cellulose in ordinary cotton there are a number of celluloid bodies derived from the inspissated juices of the cotton plant. In order to gain information on this subject, the author has grown cotton under glass, and analyzed it at various stages of its life history. In the early stage of unripeness he has found an astringent substance in the fiber. This substance disappears as the plant ripens, and seems to closely resemble some forms of tannin. Doubtless the presence of this body in cotton put upon the market in an unripe condition may account for certain dark stains sometimes appearing in the finished calicoes. The tannin matter forms dark stains with any compound or salt of iron, and is a great bugbear to the manufacturer. Some years ago there was quite a panic because of the prevalence of these stains, and people in Yorkshire began to think the spinners were using some new or inferior kind of oil. Dr. Bowman made inquiries, and found that in Egypt during that year the season had been very foggy and unfavorable to the ripening of the cotton, and it seemed probable that these tannin-like matters were present in the fiber, and led to the disastrous results.