138 



THE FROG 



alone will be suitable. The temperature of the water-bath must never 

 be allowed to rise more than a degree or two above the melting point 

 of the paraffin. Transfer the objects from turpentine to melted parafiin 

 and keep them in it for some hours — the time varies according to the 

 size of the piece — until they are thoroughly permeated. 



If you wish to cut sections by hand, get some ordinary medium-sized 

 bottle-corks : around each wind a piece of paper, allowing it to project 

 about i an inch beyond one end of the cork, and fixing it with a pin, 

 as in Fig. 43, A. Into the little cylindrical vessel or imbedding box 

 thus formed pour some melted paraffin, and immediately transfer to it, 

 by means of a warmed section-lifter or forceps, one of the prepared 



pieces, adjusting its position by 

 means of a heated needle. When 

 the paraffin is quite cold remove 

 the paper, and you will have 

 fixed to the cork a solid block 

 of paraffin containing the object 

 to be cut. 



e. Section-cutting. — Pare away 

 the block of paraffin until the 

 object comes into view : then 

 trim the block, as in Fig. 43, B, 

 until its upper surface, with the 

 object in the middle, is not more 

 than \ inch square. Hold the 

 cork firmly in the left hand, with 

 the wrist resting on the table, 

 and with a razor cut the thin- 

 nest possible slices of the paraffin 

 block, including the imbedded object. The razor must be held firmly 

 grasped at the junction of blade and handle, and kept with the surface 

 of the blade parallel with that of the block : use almost the whole extent 

 of the edge for each section. With a little practice you will be able 

 to cut sections so thin as to be quite transparent under the high power.' 



Fig. 43. — A, imbedding box made by wrap- 

 ping paper round a cork ; B, cork after 

 removal of the paper, showing the 

 parafiin pared down to a convenient 

 size for sectioning, a, object to be 

 cut. 



' If you are working in a properly furnished laboratory you will 

 probably learn how to cut sections with a microtome, or section-cutting 

 machine, which gives much better results and is absolutely necessary 

 when a complete series of sections of the same object is required. 



