50 THE MICROSCOPIC PREPARATION. 



logic features. Of these methods, we shall here describe that suggested 

 by Born (1876) and known as Bern's method of reconstruction by wax 

 plates. This method has found wide application in embryologic investi- 

 gations, and has proved very valuable in ascertaining the form, relation, 

 and metamorphosis of embryonic structures and organs. It has not been 

 so extensively used in the study of the form of fully developed anatomic 

 structures ; it deserves, however, a fuller appreciation of its value as- an 

 aid in microscopic study. Necessary are serial sections, wax plates of 

 desired thickness, and a drawing apparatus. 



Serial Sections. One of the requisites of wax plate reconstruction 

 is a perfect series of sections of uniform thickness. The thickness of 

 the sections should depend on the character and size of the object to be 

 reconstructed and on the magnification necessary to give the model ob- 

 tained such a size as to enable it to be readily manipulated. In the 

 reconstruction of fully developed anatomic structures, such as parts 

 of glands or entire glands, it is generally not possible to make an outline 

 drawing of the parts to be reproduced. When this is possible, it forms 

 the first step of the method. 



Wax Plates. Several methods have been suggested for obtaining 

 wax plates of uniform and desired thickness. The instrument devised by 



Fig. 9. Apparatus for making wax plates, used in reconstruction by Bern's method. 



Huber and figured in Fig. 9 may be recommended for this purpose. It 

 consists of a heavy cast-iron plate, supported by three adjustable legs. 

 On two sides of the plate are found movable side-pieces which may be 

 raised or lowered by micrometer screws to a desired height and then 

 tightly clamped. There is, further, a heavy iron roller which runs on 

 the adjustable side pieces. This roller needs to be heated in boiling 

 water before use, and is kept in boiling water when not in use during the 

 process of making wax plates. The method of making plates is as fol- 

 lows: The side plates are adjusted so that their upper surface projects 

 above the main plate for a distance representing the thickness of the wax 

 plate desired. Melted wax is then poured on the main plate, in an even 

 layer somewhat thicker than the wax plate desired, and then rolled out 

 with the hot roller until the roller runs evenly on the side pieces. The 

 wax plate is now allowed to cool, when it is removed from the apparatus 

 and placed in a pan of cold water, where it remains for a few minutes or 

 until thoroughly cooled. 



Drawing of the Portions of the Sections to be Reconstructed. 

 The drawings of the portions of the sections representing the portion 

 to be reconstructed, at the magnification selected, may be made with the 



