54 MATERIALS AND PROCESSES OF SLIDE-MAKING 



and leaves of botanical specimens or to the very few animal materials, such as 

 cartilage, which are suitable for the production of hand sections. 



Staining and Mounting Hand Sections. Sections are taken from the knife 

 as individual objects and are accumulated in a dish of some preservative, usually 

 70 per cent alcohol. They should be treated as wholemounts 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. 



Parafi&n Sections. Preparation of paraffin sections is quite a complex oper- 

 ation and involves the following stages: 



1. Fixation of the material. 



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 mis- 

 cible with, molten wax. 



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

 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 sections of the block into ribbons. 



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 the second 

 section of this book 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 6 for the fixation 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, however, is based 

 more on the nature of the detail which 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 formulae for the solutions 

 involved, are given in Gray's Microtechnique to which reference should be made 

 by the student seeking special information. For elementary histological prep- 

 arations, the fluids of Zenker, Gilson, or Petrunkewitsch, the formulae for 

 which are given in Chapter 2, are all excellent. 



