40 THE MICROSCOPE. 



generally the ends are square. Sometimes the cells are of nearly the 

 same length as their breadth, though generally much longer. The 

 secondary deposits on the cell wall are quite uneven, so that some 

 cells have a much larger central cavity than others, and occasionally 

 a cell wall will be e.xceedingly thickened. These layers of cellulose 

 peal off in strips giving a rough appearance to the surface. When 

 boiled in potasic hydrate or treated with the stronger acids faint 

 spiral markings appear on the cell walls. Jute, flax and hemp are 

 very similar though coarser than linen. 



The individual cells of jute are rather longer than those of 

 linen. Generally of a greyish-brown color appearing like dead 

 cellulose. Quite a prominent central cavity with smooth edges 

 is present, seeming to be perfectly empty. Much more uniform 

 than in linen. It is apt to break straight across when broken at the 

 ends of the cells, but breaks with a long fibrous fracture if broken 

 any where in the middle of the cell 



The fibres of silk are long, slender and rod-like, with occasion- 

 ally one. having a flattened side. When broken the ends separate 

 with a straight or a smooth fracture. They are solid having very 

 much the appearance of glass rods, no cells, no central opening, no 

 structure v.hatever. Averaging 1-1600 of an inch in diameter, 

 though some are even 1-800 of an inch in diameter. Their average 

 size is the smallest of the commercial fibres. They have a clear, 

 white color when unstained, and are semi-transparent, and highly 

 refractive. 



Wool fibres are either cylindrical or oval. The surface of the 

 fibre is covered by minute cells lying one upon another like shingles 

 on a roof, or like scales on a fish, though each scale is bordered by 

 a waving line. The value of wool for felting depends on the pro- 

 portion and size of these epidermal cells or scales. Wool fibres are 

 remarkable for their softness, fle.xibility and wavyness. These cells 

 are most beautifully seen in white hairs, that have been thoroughly 

 soaked in oil of turpentine, and mounted in Canada balsam. Soak- 

 ing wool fibres in a solution of soda will separate the epidermal cells 

 or scales from the rest of the fibre. Hairs of some animals polarize 

 light. An interesting object of this kind may be made by placing 

 two series of white hairs of a horse in Canada balsam so as to cross 

 each other at an angle and viewing them by polarized light. 



