358 METHODS. 



from the next section and transferred to the diagram in the same man- 

 ner, and so on with successive sections until a series of dots is obtained which 

 mark the outline of the organ. These dots are then connected by a continuous 

 line, which will indicate the form and correct position of the organ. Simple 

 reconstructions may be easily made by these means. When, however, more 

 complicated reconstructions are attempted, much judgment and skill are neces- 

 sary in the selecting of parts which may be successfully represented in a single 

 drawing, bearing in mind always the point of view which is assumed for the re- 

 construction, so that organs may be correctly represented in their relative posi- 

 tions, nearer or further from the observer as he looks at the drawing. After the 

 outlines are completed the shading of the parts must be added, and this often 

 requires a special degree of skill and a considerable faculty of plastic imagina- 

 tion. As examples of complicated reconstructions the student is referred to 

 figures ioo and 104, pages 163 and 165. 



Oftentimes simpler reconstructions are very helpful in which only a few 

 sections are combined, as, for example, to show the course and branches of the 

 spinal nerves in young embryos. In such a case the outline of the middle section 

 of the series proposed to be combined may be selected to give the outline of the 

 reconstructed drawing. Camera lucida drawings of this and the neighboring 

 sections to be included should be made of the desired magnification. The recon- 

 struction itself may be made upon tracing paper, which is laid successively over 

 the drawings of the sections and the parts required from each can be added 

 upon the tracing paper, which will thus combine in a single drawing the parts 

 intended to be represented. Reconstructions of this kind are easily made by 

 students and are often very instructive. 



Reconstruction with Wax Plates by Bom's Method. — The basis of this method 

 is to make in wax a magnified reproduction of the single sections, representing in 

 the wax such portions of the section as it is desired to reproduce in plastic recon- 

 struction. To this end wax plates must be made which represent a definite 

 magnification of the thickness of a section. For working by this method it is 

 usually advantageous to employ rather thick sections, say, of 20 it. If the mag- 

 nification chosen is fifty times, which is practically often convenient, then the 

 wax plates should be made fifty times 20 /i in thickness, or 1 mm. The most 

 convenient plates to work with are those from 1 to 2 mm. thick. Upon a wax 

 plate of the requisite thickness a camera lucida drawing is made. This may 

 be done with a lithographic crayon or with a fine steel point. The drawings 

 in 11st be of exactly the right magnification; in the illustration chosen, 50 diam- 

 eters. Next, the wax plate is put upon a glass or a metal surface where it lies 

 perfectly flat, and with a sharp thin-bladed knife or scalpel the outline of the 



