CHAPTER XXV. 261 



(in any way except with chromic acid) the ova are brought through 

 graduated alcohols up to that of 80 per cent., in which they are 

 hardened. They are then brought down again through successive 

 alcohols into water acidified lightly with any acid (except chromic 

 acid), and the albumen is found to become transparent and 

 dissolve. 



583. Reconstruction of Embryos from Sections. To facilitate 

 the study of series of sections, recourse may be had to graphic or 

 plastic reconstruction of the objects. 



In simple cases it may be sufficient to adopt the plan described 

 by SCHAFFER (Zeit. wiss. Mik., vii, 1890, p. 342). Careful outlines 

 of the sections to be constructed are drawn on tracing paper 

 with the aid of the camera lucida, superposed, and held up against 

 the light for examination by transparence. VOSMAER (Anat. Anz., 

 xvi, 1899, p. 269) draws on plates of celluloid, and sets them up in 

 a rack for examination. KERR (Quart. Journ. Mic. Sci., xlv, 

 1902, p. 1) draws on plates of ground glass which he afterwards 

 superposes and makes transparent by oil of cloves run in between 

 them. PENSA (Zeit. wiss. Mikr., xxvii, 1910, p. 48) takes sheets 

 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, 

 142,161). 



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 



