COLLODION AND OTHER IMBEDDING METHODS. 109 



dry, by dipping them into melted paraffin (APATHY, Zeit. 

 iviss. Mikr., v, 1888, p. 45), or, after rinsing with water, in. 

 glycerine-jelly, which may be removed with warm water 

 before cutting (APATHY, Mitth. Zool. Stat. Neapel, xii, 1897, 

 p. 372). 



Reference numbers may be written with a soft lead pencil 

 on the bottom of the paper trays, or with a yellow oil pencil 

 on the bottom of the watch-glasses in which the objects are 

 imbedded. On removal of the paper from the collodion 

 after hardening, the numbers will be found impressed on 

 the collodion. 



165. Cutting. If the object has not been stained before imbedding, it 

 may form so transparent a mass with the collodion that the arrange- 

 ment of the object and sections in the right position may be rendered 

 very difficult. It is, therefore, well to stain the collodion lightly, just 

 enough to make its outlines visible in the sections. This may bs done 

 by adding picric acid or other suitable colouring matter dissolved in 

 alcohol to the collodion used for imbedding, or to the oil used for 

 clearing. 



To fix a collodion block to the microtome 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 or the infiltrated and hardened but not 

 imbedded object, and 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 or 

 object. Then throw the whole into weak (70 per cent.) 

 alcohol for a few hours, or even less, or, better, into chloro- 

 form, or vapour of chloroform, for a few minutes, in order 

 that the joint may harden. 



LINDSAY JOHNSON prefers a mixture of beeswax, 1 part ; 

 rosin, 2 parts. To use it you must get the block of 

 celloidin perfectly dry at the bottom, then warm the object- 

 holder slightly, if possible over a flame ; drop on to it a few 

 drops of melted cement, and press on to it the block of col- 

 lodion, which will be firmly fixed as soon as the cement is 

 cool that is, in a few seconds. 



For objects of any considerable size it is best not to use 



