Talk:Paper - A modification of the technique of wax plate construction (1939)

From Embryology




By C. S. HALLPIKE?! anp E. W. PEET? Ferens Institute of Otology, Middlesex Hospital, London, W.1

Fot.towinc the classical method of wax plate reconstruction devised by Born, the image of the histological preparation is projected downwards by means of a vertically disposed optical system on to a sheet of paper. It is viewed by reflection from the surface of the paper and is then traced in pencil by hand. The paper is incorporated with a wax plate, the thickness of which is arranged to correspond to the linear magnification of the image, and the enlarged reproduction of the histological section is finally cut out witha sharp knife. This procedure has been modified in the following way :

The image is projected by means of a horizontal photomicrographic apparatus of conventional design on to a plate glass screen. This is rigidly supported upon a



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Fig. 1.

sliding wooden frame-work. On the back of the plate glass a wax plate is laid and retained in position by means of spring clips. The plates may be obtained ready made to any specified dimensions from the Dental Manufacturing Company, and at a cost below that of the raw material required for their manufacture in the laboratory.

The image is focused upon the surface of the wax which is in contact with the plate glass, the wax thus acting as a ground glass surface. The optical arrangements are shown diagrammatically in the accompanying figure. The optical qualities of the image are closely comparable to those upon a fine-grain ground glass screen.

The cutting out process is carried out directly upon the wax plate, the image being viewed throughout by transmitted light. In order to avoid dazzle all excised pieces of wax are left in situ until the cutting out is complete. The advantages of the procedure described are as follows:

1. Use is made of a photomicrographic bench of conventional type. Such an apparatus is likely to be part of the standard equipment of any laboratory, and further to comprise the best optical system available therein.

1 Foulerton Research Fellow, Royal Society. 2 Bernhard Baron Research Student. 128 Anatomical notes

The necessity for an additional and in any case less perfect optical system is thus obviated.

2. The considerable labour and laboratory space required for the preparation of the wax plates is avoided by the use of ready-made plates. This involves no increase of cost.

8. The two operations of tracing and cutting out are reduced to one by direct cutting out of the image projected upon the wax plate. This reduces greatly expenditure of time, and increases accuracy.

4, Accuracy of working is greatly favoured by the optical and mechanical conditions which result from the use of transmitted light and of a rigidly supported screen of plate glass. In the conventional type of procedure the eye and hand of the operator are between the image and the light source. This necessitates considerable obliquity of the line of vision relative to the surface of the paper and leads to inaccuracy of working both for geometrical reasons and from the introduction of shadows.

By the use of transmitted light it is possible throughout to maintain the eye and the point of the cutting instrument at right angles to the plane of the image, and no shadows can be introduced. Accuracy of cutting is further facilitated by the use of a rigidly supported glass screen at the eye level of the operator in a comfortable sitting position.

Acknowledgements are made to Prof. Waterston for kindly informing one of us (E.W.P.) that ready-made wax plates are now commercially available.