Dehydrating and Clearing 101 



ding in paraffin, because the oil is almost impossible to remove com- 

 pletely and will destroy the good cutting qualities of the embedding 

 medium selected. 



For clearing or dealcoholizing objects intended for embedding in wax, 

 it is customary to use a hydrocarbon, and xylene is in almost universal 

 employment at the present time. From the point of view of physical 

 properties, there is little choice between bgpzene, xylene, and toluene; 

 the author considers that the first of these has a distinct advantage in that 

 it tends to render objects less brittle . All three are equally miscible with 

 molten paraffin, but none is as good a solvent of solid paraffin as is chloro- 

 form. Both the hydrocarbons and chloroform are very sensitive to water, 

 so that it is essential that an object be completely dehydrated in alcohol 

 or dioxane before being transferred to one of these clearing agents. It 

 occasionally happens that it is impossible to provide perfect dehydration, 

 and then one is forced to utilize the "coupling" properties of phenol, 

 which is usually employed in the following mixture: 



Carbolxylene: 



Xylene 70 ml 

 Phenol 30 g 



The exact proportion of the ingredients varies somewhat according to 

 preference, but the proportion given above is the most customary. Speci- 

 mens may be taken directly from 50 per cent alcohol into this reagent 

 which, however, must be removed thoroughly by washing in pure xylene 

 before the specimen is transferred to wax. It should be pointed out to the 

 inexperienced student that phenol is capable of giving a most unpleasant 

 burn and that carbolxylene itself should be kept away from the hands 

 under all circumstances. This reagent is also useful when one is endeavor- 

 ing to clear objects in hot humid weather in summer. The alcohol used for 

 the dehydration absorbs water so rapidly under these circumstances that 

 it is almost impossible to clear satisfactorily in xylene alone. 



In the case of small objects, no special precautions need to be observed 

 in the technique of dehydrating. That is, one may merely place the object 

 at the bottom of the tube, fill the tube with the required strength of alco- 

 hol, and change this for stronger alcohol as often as becomes necessary. 

 This technique, however, cannot be employed if one is dealing with large 

 objects, since there is a tendency for the water abstracted from the object 

 to accumulate at the bottom of the tube and thus prevent satisfactory 

 dehydration, pbjec ts of a size larger than a grain of corn should always 

 be suspended from the top of the vessel containing the dehydrating agent 

 either in a small bag of cloth or, where the nature of the object permits, 

 from a hook inserted into the cap of the tube or jar. These remarks do not 

 apply when one is dehydrating with cellosolve, which is denser than water. 



