Cooper, Robert M.

Kirk, Paul L.

English

Northwestern University Illinois, School of Law: Scholarly Commons

Journal of Criminal Law and CriminologyVolume 44 | Issue 1 Article 141953An Improved Technique for Sectioning HairsRobert M. CooperPaul L. KirkFollow this and additional works at: https://scholarlycommons.law.northwestern.edu/jclcPart of the Criminal Law Commons, Criminology Commons, and the Criminology and CriminalJustice CommonsThis Criminology is brought to you for free and open access by Northwestern University School of Law Scholarly Commons. It has been accepted forinclusion in Journal of Criminal Law and Criminology by an authorized editor of Northwestern University School of Law Scholarly Commons.Recommended CitationRobert M. Cooper, Paul L. Kirk, An Improved Technique for Sectioning Hairs, 44 J. Crim. L. Criminology & Police Sci. 124(1953-1954)AN IMPROVED TECHNIQUE FOR SECTIONING HAIRS*Robert M. Cooper and Paul L. KirkPaul L. Kirk, Ph.D., is Professor of Criminalistics, School of Criminology,University of California, Berkeley, and a member of the editorial board of thisJournal. His latest text, Crime In'vestigation, which deals laboratory methods inthe police field, has recently been published.Robert M. Cooper is a graduate student in the School of Criminology, Universityof California, Berkeley.-Editor.While most of the morphological features of hair, both animaland human, can be distinguished by an experienced microscopist withoutpreparation of either transverse or longitudinal sections, it is some,times necessary and usually desirable to observe the hair at least incross section. This becomes especially true when dealing with animalhairs, the transverse aspect of which is often highly diagnostic of afamily with modifications in the genera. Many techniques have beendescribed for this operation, but in practice much difficulty is encoun-tered in embedding the hair so that it gives a true cross section whichis representative. Embedding in paraffin' alone ordinarily allowsthe hair to bend ahead of the cutting edge, leading to an angularsection which, when observed transforms a circular form into anapparent elliptical shape thereby distorting the true contour of thefiber. Embedding in collodion 2 is somewhat more successful, but thecollodion coated hair must ordinarily be mounted secondarily in paraf-fin in order to make it rigid. One is thereby confronted with the sameproblem of bending and distortion. In addition, these procedures areexcessively time consuming, and the fibers are not observable duringthe cutting process. A small microtome has been developed by Hardy3with which a person, after some experience, can make a cross sectionin a very short period of time. However, the instrument, being intendedprimarily for the study of fibers in the textile industry, requires theuse of a comparatively large bundle of fibers from which a great manysections are obtained. Of course, such an instrument is unsuited foruse in a criminalistics laboratory where the quantity of material avail-able for study is always limited.Mathiak4 described a method of embedding hairs in a celluloid-Aided by a grant from the Research Committee of the University of California.1. Smith, S., and Glaister, J., Recent A4dance in Forensic Medicine, Philadelphia, P.Blakiston's Son and Co., 1931, p. 87; Roberts, J.A.F., "A Method of Preparing Sectionsof Mammalian Hair," Textile Institute Journal, 14, T 114, 1923.2. Hotte, G.H., "The Fiber Candle Improved to Permit Quicker and Better Preparationof Specimens for Microscope," Textile World, 85, 1063, 1935.3. Hardy, J.I., "A Practical Laboratory Method of Making Thin Cross Sections ofFibers," Circular No. 378, U.S. Dept. Agr., 1935.4. Mathiak, H.A., "A Rapid Method of Cross Sectioning Mammalian Hairs," Journal ofWildlife Management, 2, 162, 1938.TECHNIQUE FOR SECTIONING HAIRSacetone medium on a strip of balsa wood. After adequate drying, asection was cut freehand through the cellulose acetate layer, hair, andwood base, all of which was then mounted on a slide. The extraneouswood material has been found to be of no particular value as claimedby Mathiak but, in fact, led to the difficulty of separating the hairsections from the balsa fibers. Sectioning of various regions of thesame hair was difficult as the wood block was cut in pieces with everyinitial cut of a series. Freehand cutting was also not desirable becauseof the thickness and lack of reproducibility of the resulting sections.It was said that sections varied from 0.3-1.0 mm. in thickness.The wood, on the other hand, provided an excellent, firm supportfor the hair and was conducive to true right angle cuts. The techniquedescribed here combines embedding on a wood base with use of ahand microtome which allows sections of 0.01-0.015 mm. in thickness,or thicker, to be obtained consistently even by the novice. Woodis eliminated from the initially cut material, and sections may be maderapidly from proximal, medial, or distal regions of the same hairwhich is always visible. Furthermore, the continuity of the whole isnot destroyed by cutting of the balsa block.EXPERIMENTALStrips of balsa wood 1 cm. wide and 3 inches long are cut from Yinch thick balsa planks. On oie of the centimeter-wide surfaces asingle layer of cellulose-acetate glue is applied and spread out evenlyto cover completely the wood strip in its central portion. Slow drying"Comet" model airplane cement has been found to be readily avail-able, convenient to use, and quite satisfactory as an embedding medium.While the film of cement is still wet the hair or hairs to be sectionedare laid on it parallel to the long axis of the balsa base. Then, as thefilm becomes tacky, a second layer of the embedding medium is appliedand spread to completely cover the hairs. The block, labeled on thereverse side, can then be placed in a closed container, such as a smallbox,- to- dry slowly.Two precautions should be observed in the embedding procedure.-No more than the necessary two layers of cement are to be appliedbecause thicker films are much more difficult to cut. Also, it hasbeen found advisable not to accelerate the drying process since numer-ous and abnormally large bubbles are thereby formed which if theysurround the hair, tend to decrease the tenacity with which it is held.Upon drying, small bubbles are seen throughout the embedding medium,1953]ROBERT M. COOPER AND PAUL L. KIRKbut they do not ordinarily interfere with the quality of the final sec-tions. Sections may be cut within 2 hour if necessary, but they arethick and wedge-shaped since the embedding cement is not completelydry, tending to yield in front of the cutting edge. At least twelvehours, or over night, is recommended as a satisfactory drying time toinsure the film being completely dry and hard.The hair to be sectioned must be clean and dry before embedding.This is achieved by thorough washing in acetone or alcohol-ethermixture and drying on filter paper in the open air for a short while.The process need not take longer than a few minutes. If a numberof hairs of a known source are to be embedded on the same block,they may be oriented, while drying, so all proximal or distal extremitiesare in the same direction. This procedure facilitates handling of thespecimens while being affixed to the block.After thorough drying, the wood strip carrying the embedded hairis placed in the specimen clamp of a table model hand microtome,e.g. American Optical Model 900. The microtome is then adjusteduntil the portion of the hair that is desired for sectioning is even withthe blade holder guides. A razor blade holder, designed for the instru-ment, is used always with a fresh, sharp blade. The cut is made, witha short slicing motion, through the embedding layers and hair, but onlyas far as the underlying wood base. The next cut is made in thesame fashion after' advancing the blok the amount desired. As mknycuts may be made successively as required.In the event that another portion of the hair must be sectioned,the block is adjusted to the region of interest and the cutting processis repeated. As the fiber is always in view through the cellulose-acetatelayer it is very convenient, for example, to obtain sections close to thednds, in the center, or any other area of the hair. The severed butunsectioned parts of the hair remain attached to the uncut block intheir original relative position and may be recovered by dissolvingaway the lacquer with acetone. The block has suffered little damageand may be resurfaced with sand paper and used repeatedly.The hair sections, set in a slide of cellulose-acetate 0.5-1.0 m.m. deepand 1 cm. wide, are lifted from the block with a pair of fine-tippedforceps and placed in a small evaporating dish. The lacquer is dis-solved with 1-2 ml.. of acetone. Upon evaporation of the acetone itwill be noticed that the resolidified celloulose acetate has migrated upthe sides of the dish leaving, the clean, free sections in the bottom.While they are under observation with a stereoscopic binocular micro-[Vol. 44TECHNIQUE FOR SECTIONING H.41RSscope, the sections are transferred to a previously albumized slideby touching each with the tip of a sharpened dissecting needle, towhich they cling, and then depositing them on the slide. The slideshould be inspected briefly under the stereoscopic binocular micro-scope, and any sections which are observed to be standing on edgecan be gently teased into their transverse plane with a needle. Analternate and slightly faster procedure is to separate the lacquer slicesand mount them on a slide. However, the lacquer slice surroundingthe hair sections interferes somewhat with definition of the contourof the hair.A permanent mounting medium and cover slip is then applied tothe preparation by standard techniques. Clarite "X" dissolved inXyol has been found to be excellent for the purpose. In addition toits mounting properties the medium infiltrates the hair and clears itnicely for observation.SUMMARYThe described method of cross sectioning hairs has been found to bewell adapted to the requirements of the criminalist. Hitherto, thisaspect of hair examination was often avoided because of the lengthyprocedures required for embedding and the uncertain results obtainedtherefrom. This technique, requiring only an hour for sectioningand mounting after embedding, is rapid, simple, and results are con-sistently reproducible. Material§ required are few and readily obtain-able, the most expensive item being the microtome. The type utilized,however, is one of the least expensive presently on the market. It is feltthat the more extensive use of transverse sections will, in many cases,lead to more positive identifications and comparisons of both humanand animal hairs.19531

An Improved Technique for Sectioning Hairs

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An Improved Technique for Sectioning Hairs

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