76 MICROSCOPICAL TECHNIQUE. 



clamp of the microtome. Solution No. 3 is poured over the 

 block ; into this the celloidin block is pressed, after dipping the 

 under surface in solution No. i. Place in chloroform until 

 hardened. 



Reconstruction points are often very desirable. For this 

 purpose the ordinary metallic embedding box, made of two L- 

 shaped pieces, held in place by overlapping strips, is used. The 

 ends and sides are perforated in as many places as desired by a 

 very small drill. The holes should be so drilled that the silk 

 threads which are drawn through run parallel. After being drawn 

 tightly, they are cemented to the sides of the box by a drop of 

 celloidin. Five or six cm. of the thread should be left hanging. 

 The bottom of the box is made by fitting in a piece of heavy 

 blotting-paper. The object is placed upon the threads in the 

 desired condition and the embedding mass poured in. As soon as 

 hardened, the celloidin holding the threads is dissolved by a drop 

 of ether. The loose ends are soaked in solution No. 2, which has 

 been thickened by the addition of lampblack. The threads are 

 then drawn through, leaving the lampblack adhering to the celloi- 

 din, thereby forming excellent reconstruction points. 



For small objects, where reconstruction points are not needed, 

 the following method may be advantageously employed : — The 

 heads are clipped from fine insect-pins, which are then placed in 

 handles in such a way that they may be easily removed. On these 

 pins the objects are oriented in the desired condition. The pins 

 are then removed from the handles and fixed in a cork, previously 

 perforated by a somewhat larger pin. As fast as the pins carrying 

 the objects are inserted the cork is replaced in the tube, which is 

 filled wuth alcohol. A half-dozen fish or amphibian ova may be 

 oriented on the same cork. If desirable to draw the objects in 

 situ, a piece of lead may be pinned to the cork and the whole 

 immersed in alcohol. The corks carrying the oriented objects are 

 transferred successively to tubes containing the different solutions. 

 When ready for final embedding, a piece of porous paper is 

 wrapped about the tubes and cork and pinned. The cork is now 

 removed, allowing the embedding solution to fill the paper tray thus 

 formed. A lead is fastened to the cork and the whole placed in 

 chloroform until hardened, after which the paper is cut from the 



