RECOKSTRGCTION r N rJow MELIEF ON SHEET CELLULOID OR GELATIN H. D. SENIOR Department of Aimtomy, Belleme Medical College, New Pork 17niaer.Tity It is usual for more reconstructions to accumulate during the course of a morphogenctic study than it is desirable to reproduce. This appears to be inevitable, but the time spent in purely technical work and the perishability of plastic reconstructions are serious disadvantages. I have tried during the past two years t o reduce these disadvantages to a minimum bv using a modificatioii of the glass-plate technique, in which sheet celluloid or sheet gelatin is substituted for glass. Eecoiistructions made with these materials share with those made on glass the limitation of requiring to be viewed perpendicularly to the plane of section in which the embryo has been cut. Their comparative lack of depth does not interfere seriously with their intelligibility and for purposes of reproduction it is a positive advantage, for the outlines can readily be traced. Provision for viewing the reconstruction in its true proportion may be made by alternating drawings on the thinner material with glass plates of appropriate thickness, although I have never found it necessary to use such a proccdure. In order that the edges of the glass plates used in an ordinary glass reconstruction may coincide exactly, a preliminary drawing is required to be made on paper and subsequently oriented and traced. The comparative simplicity of registering consecutive drawings made directly on sheet celluloid OF gelatin, which, if necessary, can be trimmed afterward with scissors, reduces the technical procedure to a minimum. A series of drawings made on such sheets and attached in serial 115 116 H. D. SENIOll ordcr constitutes a reconstruction more quickly madc and as insti*uctivefor many purposes as those prepared by the currently used plastic and graphic. methods. The reconstructions are casily stored and are practically imperishable. Sheet celluloid may be bought from the Eastmaii Kodak Co. 8 s Transparent Kodaloid no. 1,in sheets 0.002 inch thick. Similar material 0.005 iiicli or thicker is supplied by tlie same firm, but bechomes too opaque when many sheets are used. It may be used conveniently for many othcr purposes, however, wliich do iiot entail superimposing too many sheets. The expense of the thinner material (twenty-five cents per square foot) led me to invcstigatc the qualities of the thin sheet gelatin commoiily used f o r wrapping candy boxes. This is iiifcrior to celluloid in that it tears rathcr easily and that wetting it must be avoided. Rut with ordinary precautions it gives vcrp satisfactory results. METIIOD A cwwatcly rectangular sheets of celluloid or gelatin are first cut to the required size. F o r this pnrpose, I place the matcrinl over a large piece of ‘beaver board,’ markcd with conveniently spaced lincs aiid cut with a sharp kiiifc guided by a metal squarc. The ordinary cardcutter is.apt to let tlic material slip, thus distorting the angles. India ink does not mark well on a greasy surface, and sheets fiiigercd in cutting should be wiped with cz cloth moisteiied in 95 per cent alcohol. Trouhle in this regard may he avoided by wearing cotton gloves while cutting. For drawing, a projection microscope is most coiiveniciit. The first section is centcred and a sheet of the material placed 011 a drawing-board small enough to bc moved easily within tlie space available. The drawing-board is then moved until the projected image of the section falls in the correct position oil the sheet. To hold tlie sheet firmly on tlic board, fiat lead ~, below with pieces ~veightsof various sizes are I ~ R C C covered of inner tire-tube. Sheet lead and rubber map 1)c made to adliere by means of tlie thick sliellac commoiily used in R E C O N S T R U C T I O N IN CELLULOID OR GELATITS 117 garages. The required structures in the first section are now drawn upon the sheet in India ink with a thin pen, and the projected image of a second section is accurately superimposed upon the drawing of the first. This can quickly be done by moving the drawing-board until the drawing of the first section fits the projected image of the second. A small metal square is then fitted around two adjacent sides of the first sheet, which is numbered, removed, and replaced exactly by a second sheet. After the projected image of the second section has been traced on the second sheet, the image of a third section is made to fit the drawing of the second, \vhich, in its turn, is numbered and removed; the procedure being repeated until the drawings have been finished. It will be found convenient to arrange the section numbers on the sheets with a view to their simultaneous visibility after the drawings have been superimposed in order. The section to be placed at the bottom of the finished reconstruction is now put on a white sheet of paper. The drawing of the next section of the series is then oriented carefully upon it, and the two sheets attached along one edge so that they may remain separate like the pages of a book. Another sheet of paper is placed between the drawings and a third section oriented on the second, and so on, until the entire series of sheets has been attached in one or several batches. For attaching celluloid sheets, amyl acetate or acetone are more easily controllable when thickened with collodion and cause less wrinkling of the sheets. To attach gelatin sheets, I lap a moistened strip of paper (of the required length and about inch wide) along one edge of the lower sheet during the orientation of the second drawing. The paper is then removed and the part of the upper sheet over the place it previously occupied is pressed down upon the first. This method causes wrinkling of the gelatin, and some of the sheets are apt to separate when dry. To avoid subsequent separation, the moist edges of the whole batch of united sheets should be clamped tightly together while drying. There is room for improvement in the present method f o r attaching sheets. 118 H. L). SENIOIt 1)ifiercntial coloring, jf desired, is preferably finished or well started before the sheets are attached, though it is often convenient to finish it afterwml. The collodion paints on tlic market, such as Duco or Valspar lacquer, dry quickly a i d have no tendciicy to peel. Transparerit water colors wrinkle gelatin slieets aiid, sooner or later, peel off celluloid, as do the oommercial colored inks unless applied in thin lines with a pen. Brnshcs used for coloring ma)- he passed through the corks of small vials of acetone or amyl acetate far enough to Beep their bristles immersed. These can be withdrawn from the vials and dipped into paint as required, a separate brush being used for each color. Several variations of the different steps of the method liavc been tried. I n its present form and as applied 10 celluloid, it was demonstrated at the Ann Arbor meeting of the American Association of A11atomists, in April, 1928.