Making Sections 131 



author's preference is for any of the paraffin-rubber-bayberry wax mix- 

 tures. The introduction of rubber undoubtedly increases the stickiness 

 of the wax and makes it easier to obtain continuous ribbons. Bayberry 

 wax not only prevents the crystallization of the paraffin but also lowers 

 its melting point. Two of the best mixtures are: 



Hance's Rubber Paraffin: 



Stock rubber solution 



Cut 20 g of crude rubber into small pieces and dissolve, with constant 



stirring, in 100 g paraffin heated to smoking. 

 Embedding wax 



Paraffin 100 g 



Stock rubber solution 4 g 



Beeswax 1 g 



Maxwell's Embedding Wax: 



Paraffin 100 g 



Hance's stock rubber solution 4 g 



Bayberry wax 7 g 



Beeswax 1 g 



The Technique of Dehydrating, Clearing, and Embedding. Before pass- 

 ing to the choice of a microtome and the method of using it, it is necessary 

 to discuss briefly the actual operations involved in using the dehy- 

 drating, clearing, and embedding media selected. The techniques of 

 dehydration and dealcoholization do not differ materially from those used 

 in the preparation of wholemounts, which have been described. The whole 

 process, however, could be much simplified if people would only re- 

 member that water is heavier than the majority of dehydrating agents 

 and that the majority of dehydrating agents are lighter than most clear - 

 ing agents . In translating this theory into practice, it must be obvious 

 that the objec t to be dehydrated should be suspended toward the top 

 of a tall cylinder of dehydrant, in order that the water extracted from 

 it may fall toward the bottom of the vessel, and that an object to be 

 cleared should be held at the bottom of the vesse l for the reverse reason. 

 It is, indeed, practically impossible to dehydrate a large object unless it is 

 so suspended. The process of impregnating the tissues with wax has not 

 been discussed previously and will be dealt with fully. 



The first prerequisite for embedding is some device that will maintain 

 the temperature of the wax at just above its melting point. Most people 

 employ complex thermostatically controlled ovens for this purpose, but 

 the simple device shown in Fig. 91 is practical and cheap. As will be 

 seen, this device consists essentially of a series of incandescent electric 

 bulbs held at a distance, which may be varied, above a series of glass 

 vials. Before the embedding process is started, as many vials as will be 



