CHAPTER II 



REAGENTS 



While very few new reagents have come into general use since 

 the second edition of this book was published in 1905, there have 

 nevertheless been important improvements in the use of some of the 

 time-honored combinations. Doubtless the number of reagents used 

 in the histological laboratory will continue to increase, but the 

 improvements of the past eight years have been due more to increased 

 care and precision in the use of well-known reagents than to the dis- 

 covery of new combinations or ingredients. The following account 

 includes those which are used constantly, and also a few which are 

 used occasionally. The Microtomist's Vade-Mecum, by Lee, is written 

 from the standpoint of the zoologist, but it contains very complete 

 formulae for stains and other reagents. 



A list of reagents, with the quantities used by the average student 

 in a three months' course in methods, is given in chap. xxix. 

 "Stains and Staining" are described in chap. iii. 



KILLING AND FIXING AGENTS 



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 contents in as nearly the living 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. Zoologists often use chloroform or ether for killing an 

 organism, and then use various fixing agents for various tissues. No 

 promptings of humanity restrain the botanist from the vivisection of 

 plants, but separate reagents for killing and fixing are sometimes 

 used, e.g., material may be killed by placing it for a short time in 

 Flemming's fluid, which is a very rapid killing agent, after which the 

 fixing may be completed in a chromo-acetic solution, without any 



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