82 ELEMENTS OF /IPPLlED 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 modem 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 

 narrow 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 /^. U Vj" -j^ 



The cotton-fibre is mainly cellulose, covered with a fine 

 cuticula of different composition. | When treated with a 



