The Identification of Animal Fibres

Download The Identification of Animal Fibres

Post on 02-Jul-2016

212 views

Category:

Documents

0 download

TRANSCRIPT

  • The Identification of Animal Fibres A. B. WILDMAN

    Chief Biologist, W o o l Industries Research Association, Torridon, Leeds, England The following is largely a short review of the present position of that branch

    of science concerned with the identification of, particularly animal, fibres. The author's experience in this type of work has not been as a forensic scientist but has developed in response to a demand for reports on the identities and amounts of different kinds of fibres in mixtures used in the textile industry. The variety of fibres used in textiles is perhaps greater than many realise, and the gradual development over many years of a section in the biology depart- ment of the Wool Industries Research Association for work on the identification and estimation of fibres in mixtures as well as the detection of adulterants and contaminants, has developed our interest in the structure of all mammalian fibres ; we have a t times been engaged on problems of forensic interest.

    Here in outline are the principles which, in my opinion, should be followed when attempting to identify animal fibres and the fallacies which still persist and are evident in some literature. A brief indication of the several techniques available and their relative value will be given together with suggestions about the use of simple classifications of certain structural features of animal fibres. The correct interpretation of observations on fibre structure is stressed.

    The article is confined then to the subject of the structure and identification of different animal fibres ; it does not presume to advise on the collection of hairs a t the scenes of crimes nor on the examination of human hairs from different sites on the body ; the article is not concerned with materials sometimes present on fibres but extraneous to the fibre itself, and does not include such matters as types of dyes used or the "matching up" of dyed places on fibres extracted from fabrics or garments. These particular subjects are adequately discussed in existing literature (Kirk 1960, Nickolls 1956, Smith and Fiddes 1949, Glaister 1957 and others). The Principles of Fibre Identification

    First, although books and photographs are useful as guides, there is no reliable short-cut method for identifying animal fibres by simply 'matching up' the microscopical appearance of an unknown fibre with a photomicrograph ; the observer should have had experience in the examination and interpretation of diagnostic features of a variety of fibres. Secondly, and contrary to sug- gestions made in some publications, no measurement method, such as for example the measurement of distances between successive external scale margins or the measurement of fibre diameter, will itself reveal the precise origin of a fibre. Thirdly, chemical tests do not distinguish between animal fibres, since all animal fibres consist of the same substance, namely keratin. The only satisfactory procedure is to use the method of microscopy with a sound knowledge of fibre morphology and careful interpretation of the observations made.

    Variation in Fibre Structure, its Interpretation and the Type of Sample Because mammalian fibres-hair and wool-are tissues which are of course

    biological in origin, they show a wide variety in their types of cuticular-scale patterns, thickness of cuticle, form and disposition of pigment, kinds of medullae and other features recognised by examination through the microscope ; for the same reason, i.e., their biological origin, fibres from nearly related animals, for example from different breeds of sheep, often show the same kind of structure, including cuticular-scale pattern, that is if similar fundamental fibre types are compared such as a fine fibre from each breed or kemp fibres from each breed (figs. 1 and 2). Again, although the growth, shedding and replacement of fibres

  • may show different patterns in different groups or orders of mammal, the growth and shedding mechanisms are similar in many ways and therefore the root ends of shed fibres from different mammals often have a similar appearance. The investigator then should reject the false assumption that because hairs have been grown by different individual animals or different breeds or varieties of animals they are necessarily different in structure in all their parts. Fibres are, of course, often presented to the microscopist in one of a variety of forms, and if they are in assemblies such as tufts, yarn, slivers, or cloth as distinct from single fibres or fragments, care should be taken to makc sure that the sub- samples prepared for examination are truly representative of the original sample. Fibres may have suffered during wear or reprocessing when scale margins are difficult to see, and care must be taken in recognising this condition ; a suggested procedure for dealing with this kind of fibre is given below. The foregoing is perhaps sufficient to show that when attempting to distinguish between or compare animal fibres or their fragments care in making prepar- ations and objective accuracy in observation and interpretation of observations is essential. Without, I hope, being unduly righteous in this, I would say it is evident that these precepts are frequently not followed by several who claim to be experts in fibre identification.

    I t has been written, for example, that whilst the hairs of antelope and those of deer appear similar superficially, the scales of antelope hairs are 'spindle- shaped' and arranged in diagonal rows whilst scales on deer hairs are shaped like fish scales and are not arranged in rows ; a careful comparison of hairs from these two groups of animals shows however that whilst a fair length of the coarse hair of the deer has cuticular scales, the external margins of which suggest a 'fish-scale' appearance, as the tip is approached the scale pattern changes and becomes similar to that along the length of some coarse antelope hair, i.e., the scales appear to be 'spindle-shaped' and in rows (Appleyard 1960). Fragments of tip regions of some deer hairs therefore could hardly be dis- tinguished from fragments of some antelope hairs by observing their scale patterns, both would exhibit what is termed in my classification (Wildman 1954) an irregular-waved mosaic pattern. Here, as in several publications, there is evidence of a failure to recognise the fact that scale pattern often varies in form along the length of the fibres : here also examination of deer and antelope hair shows that coarse hairs from deer can be distinguished from the coarse hairs of several antelopes more by their appearance in cross-sections, and not always by the form of the cuticular-scale pattern.

    Lack of attention to the details of variation in fibres as shown by authentic samples of a wide range of types may result in the reporting and even publi- cation of features of certain fibres as characteristics for those fibres alone when in fact they may have little or no diagnostic value. When the microcopist is asked to identify fibres, it is important that he should decide from preliminary observations which type of preparation, whether a simple scale cast or rolled impression of the cuticular surface, whole mount or cross-section is likely to provide the best diagnostic criteria for identification and, if the sample is large enough, to make all these kinds of preparations. The interpretation of obser- vations on structural features of animal fibres has already been discussed briefly.

    Casts from surface of kemp fibres, x400. FIG. 1.

    Coarse fibre from Scots black-lace sheep : (a) towards the root ; (b) tip half of the same fibre. FIG. 2.

    Coarse fibre from an Indian breed of sheep : (a) towards the root ; (b) tip half of the same fibre.

    Note the similarity of the scale patterns of fibres from both breeds. 116

  • Figure 1 Figure 2

  • Before outlining techniques available and the classification of fibre characters it may be relevant to draw attention to the fact that many books on forensic medicine and forensic science have extremely sketchy sections on hair identi- fication, some, even recent publications, are inadequate and out of date in this respect ; these give little account of many useful techniques which are available and they rarely give a clear lead to students and others on the correct approach to the subject of animal fibre identification. A Brief Outline of the Most Useful Preparations to Make and the Techniques Available

    Fuller details of these are given in some of the publications listed. The kind of sample, e.g., whether a single fibre or many fibres, fragments, yam or cloth, will of course determine the procedure adopted prior to preparing the fibres for examination under the microscope.

    Whole Mounts Whole mounts of fibres are best made in a medium, such as liquid paraffin

    which has a refractive index (1.47) rather lower than that of keratin (1.548) so that whilst such features as medulla and pigmentation can be easily seen, the scale margins on the surface of the fibre are also distinguishable. If the fibres are heavily dyed, the dye should first be partially stripped from the fibres. Some fibres, if in good condition, may be identified by examination of these whole mounts. Fine camel hair, for example, with its extremely regular fibre diameter, non-projecting scales and waved-mosaic scale pattern is often easily distinguished from wool and other animal fibres : rodent and some carnivore hairs are also often readily identified from whole mounts ; if there is any difficulty, scale casts can be made and cross-sections cut.

    Scale Casts and Impressions of Cuticz~lar-Scale Patterns Sometimes, for example when fibres have been abraded or heavily re-

    processed (fig. 3), the scales are worn, projecting hardly at all from the fibre, and their margins are not easily seen in whole mount preparations : from fibres in this condition casts of the scale margins can be made in various media : polyvinyl acetate in the form of a thin film on one of two slides with the fibres stretched between and a weight on top, makes excellent casts. The slides are warmed to the melting point of the P.V.A. and then allowed to cool, the slides separated and the fibres peeled out leaving the casts. A large range of fibres gives good casts of scale patterns in this way providing valuable aids to identi- fication. However several, such as rodent fibres and those from many carnivores, have complicated patterns which change round the fibre and the only satis- factory preparations for revealing their patterns are rolled impressions (fig. 4).

    FIG. 3. Fibre taken from woollen rags and mounted in liquid paraffin. The surface of the fibre

    has been worn during reprocessing so that the scales cannot be seen. x400.

    FIG. 4. Kolled impression of the cuticular surface of part of a fine fur fibre from a rabbit. Each

    repeat of the pattern corresponds to one complete revolution of the fibre as the impression is being made. A simple whole mount or cast of such a fibre does not reveal the whole true scale pattern. x400.

    FIG. 5. Cast of the cuticular surface of a fine merino wool fibre. This photomicrograph and all

    profile preparations of this and similar fibres suggest that occasional scales are coronal : the rolled impression in fig. 6 of the same fibre disproves this conception. x400.

    FIG. 6. Rolled impression from the same fibre as that used for the cast shown in fig. 5. Nowhere

    between each pattern repeat is there only one scale : no scales on this part of the fibre are coronal. x400. W.I.R.A.

    117

  • Details of rolled impressions and their preparation are provided in other publi- cations (Wildman 1954). In this 1954 publication thcre is a classification of scale patterns and other features and when this is consulted any fibre can be classified easily and accurately. In older classifications all based on fibre- profile examinations in which the whole of the surface of the fibre is not seen and which do not always reveal the whole scale pattern, terms are used some- times mistakenly, because the fibre structure was incompletely understood, and in a confusing way : terms such as "coronal" and "annular scale pattern" have been used, and perpetuated in some quite recent publications. In fact it is extremely rare for a scale to encircle completely the fibre cortex (figs. 5 and 6) ; these terms have little value when applied to fibre profiles, because the appear- ance of the scale in profile only, is dependent upon the position in which the fibre is mounted. The term "imbricate" merely means "overlapping" but it is frequently used with no diagnostic value or accuracy in descriptions of scale patterns. Could not therefore those who describe fibres for forensic and other purposes often give simpler and more accurate accounts by using really significant and pertinent descriptive terms taken from a careful fibre classification ?

    T h e Use of Cross Sections As stated above, some fibres and samples may be identified directly from

    features seen in whole mounts, such as regularity of diameter, type of medulla, pigment type and situation and relative smoothness of the cuticle. Frequently however it is at this stage that we have a definite pointer or clue to the identity of the fibres but need further preparations to amplify or qualify the initial diagnosis. I t is in these instances that the examination of cross-sections of fibres can be a powerful aid to identification : in mixtures containing fibres from animals of the llama and alpaca tribe for example, cross-sections enable an experienced observer to identify these instantly (fig. 7). From cross-sections we can see the shape of fibre and medulla outlines when cut across, the relative thicknesses of medulla, cortex and cuticle, type of aggregations of pigment granules and where situated and the precise structure of the medulla : in such fibres as llama and alpaca, coarse camel fibres, rabbit and white calf fibres, horse hair and hog bristles, these features are quite distinct and characteristic and many fibres cannot be identified without the aid of cross-sections.

    Some form of Hardy tongue and slot microtome (Hardy 1935) is by far the best instrument to use for giving good quality sections quickly of fibres cut strictly in a plane at right angles to their long axes and not obliquely ; it is difficult to understand why so many persist in using slow, primitive and un- satisfactory methods such as the plate method when a tongue and slot device gives quickly so much better quality sections.

    Cross-sections are often invaluable for the detection of relatively cheap fibres used in textile blends or as adulterants in a variety of fabrics and brushes. They will speedily reveal the presence of various man-made and cellulose fibres which may have been used to cheapen the production of what may at first sight appear to be an all-wool fabric. Adulteration of horse hair, used in making some brushes, by the relatively cheap cow-tail hair can be detected from cross- sections ; the cow-tail hair, used as an adulterant can be detected in cross- sectional outline by several structural features and by the ring of dye near the periphery of the section, the cow-tail hair having been dyed to resemble horse

    FIG. 7. Cross-sections of brown alpaca fibres, obtained from a Hardy microtome. Characteristic

    pigment distribution with a sub-cuticular zone free from pigment. Characteristic medullae, particularly in the coarser fibres. x200. FIG. 8.

    Cross sections of horse hairs and adulterant cow-tail hairs. The peripheral zone of dye used to make the cow-tail hairs resemble horse hairs is shown. The two kinds of fibres are easily distinguished in cross-section. x100.

    W.I.R.A. 118

  • Figure 7

    7'

    Figure 8

  • hair (fig. 8). Adulteration of expensive hog bristle used in high quality brushes can also be readily detected by the examination of cross-sections.

    The value to the fibre microscopist of a permanent collection of authentic samples of fibres cannot be over emphasised. The samples should be drawn as far as possible from the live animals, and preferably in the pulled and/or shed state so that the whole fibres are obtained. The body sites from which the samples are taken, particulars of sex, age, time of year and other information should be carefully recorded. Such samples may be obtained from zoological gardens and othcr animal owncrs of good will. These should be supplemented by others from commercial sources, that is from the various industries which may process the fibres, and notes made of the stages in processing which the fibres have endured. Samples from other available sources, e.g., those collected for criminologists, should be added to the collection whenever possible. Careful study of the morphology of these fibres is essential to provide the necessary experience for any microscopist seeking to be genuinely expert in the irlenti- fication of mammalian fibres.

    References APPLEYARD, H. M., "Guide to the Identification of Animal Fibres "

    Wool Industries Research Association, Leeds, 1960 GLAISTER, J., " Medical Jurisprudence and Toxicology "

    E. and S. Livingstone Ltd., London, 1957 HARDY, J. I., "A Practical Laboratory Method of Making Thin Cross-sections

    of Fibres," U.S. Dept. Agric. Cir. No. 378, 1935 KIRK, P. L., "Crime Investigation-Physical Evidence and the Police Labora-

    tory." Interscience Publishers Inc. New York, 1960 NICKOLLS, L. C., " The Scientific Investigation of Crime"

    Buttenvorth and Co. (Publishers) Ltd., London, 1956 SMITH, Sydney, and FIDDES, F. S., " Forensic Medicine "

    J. and A. Churchill Ltd., London, 1949 WILDMAN, A. B., " The Microscopy of Animal Textile Fibres "

    Wool Industries Research Association, Leeds, 1954