COLLODION AND OTHER IMBEDDING METHODS. 107 



under a bell-jar, together with a dish containing alcohol, so 

 that the evaporation is gone through in an atmosphere of 

 alcohol. This is especially indicated for very large objects. 

 The whole process of adding fresh collodion and placing 

 the objects under the required conditions of evaporation is 

 repeated every few hours for, if need be, two or three days. 

 When the mass has attained a consistency such that the 

 ball of a finger (not the nail) no longer leaves an impress on 

 it, it should be scooped out of the dish or mould, or have the 

 paper removed if it has been imbedded in paper, and be 

 submitted to the next stage of the hardening process. (If 

 the mass is found to be not quite hard enough to come away 

 safely, it should be put for a day or two into weak alcohol, 

 30 to 70 per cent.) 



163. Hardening, Definitive. Several methods are available 

 for the definitive hardening process. One of these is the 

 chloroform method, due to VIALLANKS (Rech. sur I' Hist, et le 

 Dev des Insecte*, 1883, p. 129). 



It consists in bringing the objects into chloroform. In 

 some cases a few hours' immersion is sufficient to give the 

 requisite consistence. In no case have my specimens 

 required more than three days. The collodion frequently 

 becomes opaque on being put into the chloroform, but 

 regains its transparency after a time. 



Small objects maybe hardened by chloroform without pre- 

 liminary hardening by evaporation. All that is necessary is 

 to expose the mass to the air for a few seconds until a mem- 

 brane has formed on it, and then bring it into chloroform. 

 If the mass is in a test-tube this may be filled up with 

 chloroform and left for two or three days if need be. By 

 this time the collodion mass will be considerably hardened, 

 and also somewhat shrunk, so that it can be shaken out of 

 the tube. It is then brought into fresh chloroform in a larger 

 vessel, where it remains for a few more days until it is ready 

 for cutting. But sufficient hardening is sometimes obtained 

 in a few hours. 



Good chloroform is a necessity. 



The above processes are excellent, but I reg*ard them as 

 primitive forms of the chloroform method. I now almost 

 always harden in vapour of chloroform. All that is neces- 



