128 The Preparation of Microscope Slides 



mounts rather than as sections. That is, either they may be mounted 

 directly in gum media or they may be stained and mounted in resinous 

 media in the manner described in Chapter 6. 



PARAFFIN SECTIONS 



Preparation of paraffin sections is quite a complex operation and in- 

 volves the following stages: 



1. Fixation of the materia l. 



2. Dehydration in order that the material may be impregnated with a 

 fluid capable of dissolving wax. 



3. Removal of the dehydrating agent with a material solvent of, or 

 miscible with, molten wax . 



4. Soaking the cleared specimen in molten wax long enough to ensure 

 that it will become completely impregnated . 



5. Casting the now impregnated specimen into a rectangular block of 

 wax. 



6. Attaching this block of wax to some holder, which itself may be 

 inserted into a suitable microtome. 



7. Actual cutting of the b lock into ribbons of sections. 



8. Placing these ribbons on a glass slide in such a manner that they 

 will lie flat and that the contained section will be adherent after the wax 

 has been dissolved . 



9. Removal of the wax solvent . 

 10. Staining and mounting . 



Each of these operations will be dealt with in due order. In Part Three 

 there are a series of examples which describe in detail the application 

 of these principles to actual preparations. 



Choice of Fixative. The methods described in Chapter 10 for the fixa- 

 tion of objects for wholemounting can be used equally well if these objects 

 are to be sectioned. The selection of the fixative for blocks of tissue, how- 

 ever, is based more on the nature of the detail that is to be preserved. In 

 general, it may be said that strongly acid fixatives are best where nuclear 

 detail is required. The selection of fixatives and several hundred formulas 

 for the solutions involved are given in Gray's "Microtomisfs Formulary and 

 Guide " to which reference should be made by the student seeking special 

 information. For elementary histological preparations, the fluids of 

 Zenker, Gilson, and Petrunkewitsch, the formulas for which are given in 

 Chapter 6, are all excellent. 



Dehydrating. The classic method of dehydration is to soak the object 

 in a graded series of alcohols, usually 10 or 15 per cent apart. Dehydra- 

 tion through gradually increasing strengths of alcohol may be vital when 



