82 ELEMENTS OF APPLIED MICROSCOPY. 
35° south latitude, given proper soil and a uniform sup- 
ply of moisture. The United States, India, Egypt, 
China, and Brazil are the most important cotton-pro- 
ducing nations in the order named; though many other 
countries devote large areas to its cultivation. 
The most important process in the preparation of cot- 
ton for the market is ginning, or the separation of the 
fibre from the seed-cotton, which as picked contains 
two-thirds of its weight in seeds. The modern process, 
evolved from that which Eli Whitney was largely instru-. 
mental in developing in 1794, consists in exposing the 
cotton to the action of a series of fine-toothed circular 
saws: which tear off the fibre and carry it away through 
the grid in which they revolve. 
The fibre, as thus obtained, is a hollow ribbon (Fig. 
32) spirally twisted at frequent intervals with, the edges of. 
the ribbon so sharply marked off from the central canal 
that they appear like swollen cords.. The section of the: 
fibre is not, however, dumbbell-shaped, as this might, 
suggest, but elliptical or somewhat crescentic, the lumen 
of the canal following the outer contour. The canal is 
natrow in American and Egyptian cotton, and broader in 
that. from India. By following a single fibre carefully 
along, it will be noticed that it tapers to a somewhat 
blunt point at one end and at the other extremity is 
broken off. sharply where it was attached to the seed. 
The length of the cotton fibre varies from 20 to 40 
mm.,—its diameter, from 10 to 20 p. 
The cotton-fibre is mainly cellulose, covered with a fine 
cuticula of different composition. When treated with a 
