Structural Details of Natural Fibers as Observed 

 with the Electron Microscope 



C. Maertens, G. Raes, and G. Vandermeerssche 



Laboiatoire de Technologie des Matieres Textiles de /' Uiiiversite de Gaiid 

 and Centre de Microscopie Electionique, Medical, Industrie! et Agricole. Brii.xelles-Uccle 



Most studies with the electron microscope on the 

 fine structure of natural fibers have been limited to 

 the suspension and to the replica techniques. This 

 is mainly due to the fact that cellulose fibers are very 

 hard to cut with the usual glass knives and that no 

 quite appropriate staining techniques for cellulose 

 have been found. At the Conference of Barcelona in 

 1954 (4) and at the Conference of Brussels in 1955 

 (2) we have mentioned already our first attempts 

 of making ultra-thin sections of cotton fibers. 



Several staining methods had been tried and three 

 of those had given good results: osmic acid, ferri- 

 alum and iodine zinc chloride. 



A still better specific electron staining has been 

 found by Saara Asunmaa ( 1 ) who has made ultra- 

 thin sections of cellulose fibers after treatment with 

 thallous ethylate. The contrast obtained by this 

 method is excellent but unfortunately the method 

 of staining is quite long and elaborate. We have 

 been able to obtain equally well stained sections of 

 cellulose fibers by a very simple treatment with 

 silver nitrate. 



The fibers under investigation were dipped into a 

 20 % silver nitrate solution for a couple of hours and then 

 washed, dehydrated and embedded in the usual way as 

 described in our previous work (2). A mixture of 6/4 

 butyl-methyl-methacrylate has been found most suitable. 

 The microtome used was the Porter Blum model and the 

 sections obtained were on the average about 250 A thick. 

 The electron microscope used was the Philips type EM 

 75. 



Cotton fibers of different types and different origin 



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have been tried. Also flax fibers of different types 

 and at different stages of its treatment in the hackling 

 machine have been investigated. 



The reason for trying these many types of cellulose 

 fibers is to check in how far a particular structural 

 aspect can be considered as a possible artefact or as 

 a structure due to the drying out of the fresh fibers. 



When our first cotton sections were shown (2) 

 the question arose as to what extent certain struc- 

 tural details could have been considered as artefacts. 

 Several of the cotton sections showed indeed a kind 

 of "detachment"' of some of the layers of which the 

 secondary wall is built up. This "detachment" 

 which had never been observed before, was called 

 a "kind of secondary lumen" or "artificial lumen". 



This particular aspect of certain cotton fibers is of 

 the greatest importance because it might help in 

 explaining certain discrepancies which exist in meas- 

 urements done in different laboratories with the 

 arealometer (of Dr. Hertel). 



Fig. 1 shows such "detachments" in cotton fibers 

 which have been fixed and embedded in the same 

 way as described earlier (2). We have therefore made 

 comparisons of a whole series of fixation and staining 

 methods in order to improve our previous method. 



From these tests we may conclude that almost all 

 the fixatives used gave almost identical results in 

 so far as the shape of the fibers is concerned. As 

 regards the contrast, we have found that the treat- 

 ment with a silver nitrate solution gave by far the best 

 result. 



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Fig. 1. Transverse section of cotton fibers, fixed in OsOj. Magnification 4000. 

 Fig. 2. Transverse section of flax-fiber. AgNOg fixation. Magnification 4000. 

 Fig. 3. Longitudinal section of flax fiber. AgNOj fixation. Magnification 12,000. 



