362 EMBRYOLOGY 



of lithographic gelatin. Woodworth {Zeit. wiss. Mik., xiv, 1897, 

 p. 15) proceeds as follows : (1) Draw an axial line of the length of 

 the object multiplied by the magnification employed. (2) Measure 

 with a micrometer the greatest diameter of each section. (3) Plot 

 these diameters down transversely on the axial line at distances 

 corresponding to the thickness of the sections multiplied by the 

 magnification. (4) Join the extremities of these diameters ; this 

 will give you an outline of the object. (5) Measure off on each 

 section the nearest and farthest limits (from the margin) of the 

 organs to be filled in, and plot them down on the transverse lines 

 (3), and join the points as before, i.e. from section to section ; this 

 will give you the outlines of the organs. 



This process is best applicable to reconstruction from transverse 

 sections, but it can be applied to reconstruction from sections in 

 any plane if the object can be provided with a plane of definition 

 at right angles to the plane of section. This may be established 

 by cutting off one end of the object, or the like (see also Orientation, 

 §§ 162, 164). 



To make a simple plastic reconstruction, camera drawings (or 

 photographs) of the sections (all made at the same magnification) 

 are pasted on pieces of cardboard of a thickness equal to that of 

 the sections multiplied by the magnification employed. Then the 

 parts of the drawings representing the cavities of the objects are 

 cut out with a knife or fretsaw, cutting through the cardboard ; 

 and the pieces of fretwork thus obtained are pasted together. 



Many useful modifications of this method have been devised. 

 Cardboard is rather hard to cut, and not conveniently got of the 

 required thickness. The late Professor Arthur Thompson, of 

 Oxford, used numbers of sheets of blotting paper to the required 

 thickness, soaked in beeswax ; this makes a very tough substance, 

 and the models, when made, can be handled without chance of 

 injury ; other workers use beeswax plates alone, drawing the 

 outline with some sharp instrument and cutting out with a hot 

 knife. 



Mr. Pittock, of the Embryological Laboratory, University 

 College, London, uses a modification of K. Peter's method {vide 

 infra). Rather thin paper is used for drawing the outline of the 

 object. In this laboratory (Professor J. P. Hill), special rolls of 

 paper are used, so that the diagram of each of hundreds of sections 

 may be safely rolled vip in order till wanted. A large flat stone is 

 used for the manufacture of the wax plates, with two brass gauges 

 of the required thickness placed at a distance which will accom- 

 modate in between them the square of paper with the drawing. 

 Instead of treating the paper with turpentine, according to Mr. 

 Pittock's method, the drawing is rapidly floated over the surface 

 of a dish of water, drawing side down, then laid upon the stone, 

 between the metal gauge, and the supcrflvious nioisture smoothed 



