104 COLLODION AND OTHER IMBEDDING METHODS. 



adopted the practice of clearing before cutting with cedar oil, as 

 described in the next . 



FISH (loc. cit., 167) also advocates the practice of clearing in the 

 mass, recommending the clearing mixture there given. Similarly 

 GAGE, Trans. Amer. Mik. Soc., xvii, 1896, p. 361. 



All the authors above quoted cut in the wet way, that is to say, 

 with a knife wetted with the clearing liquid. 



169. GILSON'S Rapid Process (communicated April, 1892). The 



object is dehydrated, soaked in ether, and brought into a test-tube 



with collodion or thin celloidin solution. The tube is dipped into a 



bath of melted paraffin, and the collodion allowed to boil (which it 



does at a very low temperature) until it has become of a syrupy 



consistence. (It should be boiled down to about one-third of its 



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 chloroform : 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. 



This process is very much more rapid than the old process : small 



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



required by the old process. 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. 



170. The Dry Cutting Method. I recommend the following as a 

 further improvement. Infiltrate with collodion or celloidin either 

 by GILSON'S process, or by soaking in the cold in the usual way, 

 159. Imbed as usual. Harden in vapour of chloroform for from 

 one hour (generally sufficient 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 chloroform 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 throw it into GILSON'S 

 mixture. This should be at first a mixture of 1 part of chloroform 

 with 1 or 2 parts of cedar oil. From time to time more cedar oil 



