164 COLLODION AND OTHER IMBEDDING METHODS. 



To fix a collodion block to the microtome, proceed as 

 follows. Take a piece of soft wood, or, for very small objects, 

 pith, of a size and shape adapted to fit the holder of the 

 microtome. Cover it with a layer of collodion, which you 

 allow to dry. Take the block of collodion, cut a slice off the 

 bottom, so as to get a clean surface; wet this surface first 

 with absolute alcohol, then with ether (or allow it to dry) , place 

 one drop of very thick collodion on the prepared wood or pith, 

 and press down tightly on to it the wetted or dried surface of 

 the block of collodion. Then throw the whole into weak (70 

 per cent.) alcohol for a few hours (or even less) in order that 

 the joint may harden. 



For objects of any considerable size, it is important not to 

 use cork for mounting on the microtome, especially if the 

 object-holder be a vice, for cork bends under the pressure of 

 the holder, and the elastic collodion bends with it, deforming 

 the object. I have seen large embryos so deformed in this 

 way that the sections obtained were true calottes, segments of 

 a sphere. If the object-holder be of the cylinder type, as in 

 the later forms of the Thoma microtome, the above-described 

 accidents will be less likely to happen, and a good cork may 

 be used, but even then, I think, wood is safer. 



Sections are cut with a knife kept abundantly wetted with 

 alcohol (of 50 to 85 or even 95 per cent.). Some kind of 

 drip arrangement will be found very useful here. Apathy 

 recommends that the knife be smeared with yellow vaselin ; 

 it cubs better, is protected from the alcohol, and the mobility 

 of the alcohol on the blade is lessened. 



The knife is set in as oblique a position as possible. 



Very brittle sections may be col lod ionised as explained 

 above ( 275). 



The sections are either brought into alcohol (of 50 to 85 or 

 95 per cent.) as fast as they are made, or if it be desired to 

 mount them in series they are treated according to one of the 

 methods described below, in the chapter on Serial Section 

 Methods. 



297. Staining. The sections may now be stained in almost 

 any stain that may be desired, either loose, or mounted in 

 series on slides or on paper as described below. It is not 

 necessary, nor indeed desirable, to remove the mass before 

 staining. 



