128 Animal Microloyy 



glass slide over the surface of the wax. To prevent the plate from 

 splitting while cooling, after it has stiffened somewhat, cut the edges 

 free from the walls of the pan. When the water has become tepid, 

 remove the wax plate to a flat support and leave it to harden. 



(6) Huberts method. Several instruments have been devised for 

 making the plates more rapidly and more accurately than by the original 

 method. Huber's apparatus, for instance, consists of a heavy cast-iron 

 plate with moveable side pieces which can be adjusted to a height cor- 

 responding to the desired thickness of the wax plates. The whole 

 instrument is supported upon three adjustable legs, by means of which 

 it can be made exactly level. Melted beeswax slightly in excess of the 

 quantity necessary for a wax plate is poured on to the iron plate in an 

 even layer, and rolled out with a hot roller until the roller comes to run 

 directly on the side pieces of the instrument. When the wax plate is 

 cool enough to handle it may be placed in a pan of cold water to harden. 



Practical Exercise. When possible an outline drawing of the 

 part to be reconstructed should be made before it is sectioned. 



1. Reconstruct the heart of a chick at the end of the third 

 day of incubation, under a magnification of 60 diameters. For 

 this magnification, if it is desired to use a wax plate 2 mm. thick, 

 the original sections should have been 33.3 microns thick. 



2. Place a sheet of blue tracing-paper on the wax plate with 

 the colored side toward it. Over the tracing-paper place a sheet 

 of ordinary drawing-paper. With the aid of a camera lucida or 

 other projection apparatus, outline on the drawing-paper the part 

 to be reconstructed. In doing this the outline is also traced in 

 blue on the wax. Number each drawing, and also indicate the 

 number of the section on the slide to which it corresponds; also 

 number the wax plates with reference to the drawings. 



3. Lay the wax plate on a suitable flat surface, and cut out the 

 outlined parts with a sharp, narrow-bladed knife. Leave bridges 

 of wax to hold in place the parts that would otherwise be separate 

 pieces. Pile up the successive sections in proper sequence as 

 they are cut out. 



4. In finally putting the model together, accurately adjust the 

 parts (for reconstruction points see chap, xvi, memorandum 13, 

 II a), and build up the model in blocks of five sections each 

 (Bardeen's suggestion). If necessary, unite the essential parts 



