CHAPTER IX. 101 



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 Neavel 

 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 be 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 infil- 

 trated 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 chloroform, 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 collodion, 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 cork for 

 mounting on the microtome, 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. If the object-holder be of the 

 cylinder type, a good cork may be used ; but even then, I think, 

 wood is safer. GAGE has recommended bits of glass cylinders. 

 JELINEK (Zeit. wiss. Mik., xi., 1894, p. 237) recommends a sort of 



