GENERAL MICROSCOPY 



The scale layer, a layer of flat overlapping The scale cells can best be examined with 



elements. The scales also have a fibrillary the semi-embedding methods discussed under 



structure. They consist of macro-fibrils which Surface Examination (p. 345) or by making 



can be seen in isolated scales with a phase a rephca. If the hair is pigmented it must 



microscope and micro-fibrils observable only first be bleached in hydrogen peroxide, 



with an electron microscope. In between The cortex cells. The course of the cortex 



these fibrils is the scale cement. layer can most suitably be examined with 



This heterogeneous structure of the scales normal glycerin preparations. The individual 



has led some authors to classify them as en- cortex cells can be examined by disintegrat- 



docuticula and exocuticula. But this distinc- ing the hair in caustic potash or by the 



tion has no significance in practice. trypsin-sulfuric acid method. 



The scales play an important part in the The caustic potash treatment is effected 



occurrence of crimp. Outside a curve the in 5% KOH for 2-3 hours at 50°C. The 



scales are thicker than inside and there is drawback is that the cells swell greatly, 



also more matter there. Shape and size are rather uncertain. 



Chemicals and dyes can penetrate better The better way is first to dissolve the 



into the scales inside the curve than into cement substance by the trypsin treatment 



those on the outside. and then to make a preparation in sulfuric 



The epicuticula, a membrane about 100 A acid. 



thick completely enveloping the wool hair „ . , ^. « ^r ^ • ^ no 



^ '^ r- o Trypsin solution: 0.75 g trypsin and 0.3 g so- 

 on the outside. It is very resistant to attack ^ium bicarbonate are dissolved in 100 cc distilled 

 by acids and bases. Its composition, however, water. (The sodium bicarbonate must be very 

 does not differ fundamentally from normal pure). The solution is fully active for only one 

 keratin hour. The hair is defatted properly in petroleum 



ri ,1 J. . . 1 X J.T- • ±- ^ • ether or benzene, dried, washed and cut in 0.5-1 



Some authors state that the epicuticula is . n on en u • m .^ • i 



^ mm pieces, rer 30-50 mg hair, 10 cc trypsin solu- 



the cortex cell membrane. Kassenbeck tion is used. The suspension is left standing for 3 



showed in ultra-thin sections with an electron hours in a closed Erlenmeyer flask at 40°C ± 3°C. 



microscope (1) that the scale edges which are Sulfuric acid: 85 parts analytically pure sulfuric 



visible under the normal microscope are ^^.i^, s.g. 1.84 and 15 parts distilled water are 

 ridges on the actual scales which envelop the 



fiber like a cuff ; (2) that the epicuticula was The cortex mantle can best be prepared by 



membrane enveloping the scale. treating the wool fibers with 1.6% peracetic 



acid followed by extraction with 0.1 iV am- 



Methods of Examining the Various Fiber j^onium hydroxide. The insoluble portion is 



Elements 7-10% of the fibers. A cross-section shows 



The epicuticula. The structure of the epi- that besides the cortex mantle the cell mem- 



cuticula can be examined with Von All- brane of the cortex cells can also be seen, 



worden's reaction. The defatted wool is while in phase contrast part of the scales is 



placed in saturated bromine solution and is also found to be present, 



examined through a microscope until the The medullary sheath. The size and course 



first blisters occur. Water is then sucked of the medullary canal can best be studied 



through, the blisters usually increasing in from a longitudinal preparation. To study 



size. The blisters may be stained with 0.1% the size and shape properly, the air in it 



methylene blue. The time elapsing before the must be expelled. 



first bhsters occur and the shape and size of The most effective way to do this by lay- 



these bhsters are important and may be used ing short pieces in KOH or turpentine. A 



as important characteristics to detect dam- 17 % KOH solution at room temperature is 



age. mostly used. If the 17% KOH solution is 



352 



