COLLODION AND OTHER IMBEDDING METHODS. 133 



volume.) The mass is then turned out, mounted on a block 

 of hardened celloidin, and the whole hardened in chloroform 

 or in a mixture of chloroform and cedar oil for about an hour. 

 It is then cleared in cedar oil (if hardened in pure chloro- 

 form : special clearing will not be necessary if it has been 

 hardened in the mixture). It may now be fixed in the 

 microtome and cut, using cedar oil to wet the knife, and 

 cover the exposed surface of the object after each cut. 



It will be observed that this process is very much more 

 rapid than the old process in two ways. The celloidin 

 bath, being given warm, is greatly abridged ; small objects 

 can be duly infiltrated in an hour, where days would be 

 required by the old process. And the hardening is very 

 much more rapid than hardening by alcohol, which requires 

 at least twenty-four hours. As collodion boils at a very low 

 temperature very little heat is required, and there is no risk 

 of the tissues suffering on that head. 



165. The Dry Cutting Method. I recommend the following 

 as being a further improvement. Infiltrate with collodion 

 or celloidin either by GILSON'S process, or by soaking in the 

 cold in the usual way, 153. This is a much slower pro- 

 cess, but does not take up more of the worker's time, as the 

 specimens require no attention whilst in the bath. Imbed 

 as usual, either directly on the holder of the microtome, or 

 in a paper tray or a water-colour mould or the like. Harden 

 in vapour of chloroform for from one hour (generally suf- 

 ficient for small objects) to overnight. This is done by 

 putting the object (definitively imbedded in the final thick 

 solution, but without any preliminary hardening in the air) 

 into a Steinach's sieve-dish or into a desiccator, on the 

 bottom of which a teaspoonful of chloroform has been 

 poured. (The objects may remain for months in the chloro- 

 form vapour if desired.) As soon as the mass has attained 

 sufficient superficial hardness, it is, of course, well to turn it 

 out of its recipient, and turn it over from time to time, in 

 order that it may be equally exposed on all sides to the 

 action of the vapour. When fairly hard (it is not necessary 

 to wait till the mass has attained all the hardness of which 

 it is susceptible) throw it into GILSON'S mixture. This 

 should be at first a mixture of one part of chloroform with 



