COLLODION AND OTHER IMBEDDING METHODS. 113 



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 tea- 

 spoonful 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 one part of chloroform with one or two parts of 

 cedar oil. From time to time more cedar oil should be 

 added, so as to bring the mixture up gradually to nearly pure 

 cedar oil. As soon as the object is cleared throughout, the 

 mass may be exposed to the air, and the rest of the chloro- 

 form will evaporate gradually. The block may now either 

 be mounted on the holder of the microtome, 165, and cut 

 at once, or may be preserved indefinitely without change in 

 a stoppered bottle. Gut dry, the cut surface will not dry 

 injuriously under several hours. The cutting quality of the 

 mass is often improved by allowing it to evaporate in the air 

 for some hours. 



The hardening may be done at once in the chloroform and 

 cedar oil mixture, instead of the chloroform vapour, but I 

 find the latter preferable. And clearing may be done in 

 pure cedar oil instead of the mixture, but then it will be 

 very slow, whereas in the mixture it is extremely rapid. 



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