106 CHAPTER IX. 



tions bubbles make tlieir appearance in the mass. Before 

 proceeding with the hardening these should be got rid of 

 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. wiss. Mik., viii, 1892, p. 467). 



161. Orientation. Celloidin being more or less transparent, 

 it is seldom necessary to recur to special aids to orientation. 



APATHY (Zeit. wiss. Mik., v, 1888, p. 47) arranges objects 

 on a small rectangular plate of gelatin, placed on the bottom 

 of the imbedding-recipient. The gelatin is turned out with 

 the mass after hardening, and cut with it. The edges of 

 the gelatin form good orientation lines. 



HALLE and BORN (Zeif. ic-iss. Mil:., xii, 1896, p. 364) use 

 plates of hardened white ot egg, in which a shallow furrow 

 for the reception of the objects has been cut by means of a 

 special instrument. See also 142. 



For the complicated method of EYCLESHYMER (Amer. Nat., 

 xxvi, 1892, p. 354) see previous editions. 



See also the article " Eekonstruction '' in the Encycl. mik. 

 Technik. 



162. Hardening, Preliminary. The objects being imbedded, 

 the treatment should be as follows :- -The receptacles or 

 supports are set with the mass under a glass shade, allowing 

 of just enough communication with the air to set up a slow 

 evaporation. Or porcelain moulds or small dishes may be 

 covered with a lightly fitting cover. As soon as the added 



9 fc 



thick collodion (of which only just enough to cover the 

 object should have been taken) has so far sunk down that 

 the object begins to lie dry, fresh thick solution is added, 

 and the whole is left as before. (If the first layer of 

 collodion has become too dry, it should be moistened with a 

 drop of ether before adding the fresh collodion.) Provision 

 should be again made for slow evaporation, either in one of 

 tho ways above indicated, or- -which is perhaps better by 

 setting the objects under a hermetically fitting bell-jar, 

 which is lifted for a few seconds only once or twice a day. 

 I have frequently found it advantageous to set the objects 



