124 OHAPTEE IX. 



as being very convenient for collodion imbedding. The 

 bottoms, however, should be made of soft wood in preference 

 to cork ; cork is elastic, and bends in the object-holder of 

 the microtome, deforming the mass and object. The box 

 should be prepared for the reception of the object by pouring 

 into it a drop of collodion, which is allowed to dry. The 

 object of this is to prevent bubbles coming up through the 

 wood or cork and lodging in the mass. 



Objects may also be imbedded on a piece of pith or 

 leather, which should also be prepared with a layer of dry 

 collodion. 



Watch glasses, deep porcelain water-colour moulds, and 

 the like, also make convenient imbedding receptacles. Care 

 should be taken to have them perfectly dry. 



It not unfrequently happens that during these manipula- 

 tions bubbles make their appearance in the mass. Before 

 proceeding with the hardening these should be got rid of. 

 This may be done by exposing the whole for an hour or two 

 to the vapour of ether in a desiccator or other well-closed 

 vessel. Care should be taken that the ether (which may be 

 poured on the bottom of the vessel) does not wet the mass 

 (BussE, Zeit. f. n:i*s. Mik., viii, 4, 1892, p. 467). 



155. Orientation. If it be desired to mark the position of the object 

 in the mass in order to facilitate the subsequent orientation of it on the 

 object-holder of the microtome, recourse may be had to the method described 

 by EYCLESHYMER in Amev. Nat., xxvi, 1892, p. 354 (see also Journ. Boy. 

 Mic. Soc., 1892, p. 562). The object is imbedded in one of the metal 

 boxes described in 126. The box lias its ends and sides perforated at 

 regular intervals by small opposite holes. Silk threads are passed through 

 these holes from side to side, stretched, and kept tight by sticking them to 

 the sides of the box by means of a drop of celloidin, leaving a length of a 

 couple of inches hanging loose. The loose ends are soaked in thin celloidin 

 solution with which lamp-black has been mixed. The object is arranged in 

 position on the framework formed by the taut threads in the box, the mass 

 is poured in, and the whole is hardened. After hardening, the celloidin 

 holding the cuds nf the threads is dissolved by means uf a drop of ether, 

 and the lampblacked ends are pulled through the box. This leaves 

 adheriu"- to the bottom of the mass a series of black lines which form. 



il 



orientation points. 



A CATHY (Zeit. f. wi*. JTV/r., v, 1, 1888, p. 47) arranges 

 objects 011 a small rectangular plate of gelatin, placed on the 

 bottom of the imbedding-recipient. The uvlatin is turned 



