CHAPTER II 



REAGENTS 



During the eight years since the fourth edition of this book ap- 

 peared, practically no new ingredients of formulas have come into gen- 

 eral use; but there have been new combinations of ingredients and 

 considerable improvement in the use of reagents. The following ac- 

 count presents not only those reagents which are in constant use but 

 some of those which are used only occasionally. The Microtomist's 

 Vade-Mecum, by Lee, is written from the standpoint of the zoologist, 

 but it contains very complete formulas for stains and other reagents 

 which are equally valuable to the botanist. 



For convenient reference, a list of reagents, including stains, is given 

 in chapter xxxi. Stains are treated more fully in chapter iii. 



KILLING AND FIXING AGENTS 



No process in microtechnique is in more urgent need of improve- 

 ment than this first step of killing and fixing. In nearly every investi- 

 gation involving histological technique some fixing agent or other is 

 recommended; but usually so little attention is paid to other factors 

 which may be just as important, that it is doubtful whether the fixing 

 agent is responsible for the excellence or mediocrity of the prepara- 

 tions. If the fixing is bad, it is impossible to get good preparations; but 

 insufficient washing after fixing, too rapid dehydration, too long an 

 immersion in the paraffin bath, or too high a temperature in the bath 

 may result in poor preparations even when the fixing has been good. 

 If material is examined at every stage, mistakes can be corrected — in 

 the next lot of material. 



Usually the same reagent is used for both killing and fixing. The 

 purpose of a killing agent is to bring the life-processes to a sudden 

 termination, while a fixing agent is used to fix the cells and their con- 

 tents in as nearly the Uving condition as possible. The fixing consists 

 in so hardening the material that the various elements may retain 

 their natural condition during all the processes which are to follow. 



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