CHAPTER 5 



Primaij Fixatives Considered 

 Separately 1 . Coagulants 



The term 'primary fixatives' is used here to mean single fixative 

 substances as opposed to mixtures of tvvo or more in a single solu- 

 tion. Primary fixatives may be used either absolutely, as ethanol, 

 for instance, is sometimes used; or in solution in distilled water; 

 or in solution in water with an indifferent salt. 



The action of fixative mixtures can only be understood through 

 a process of analysis. It is for this reason that the preceding 

 chapters have been concerned almost entirely with primary fixa- 

 tives. In this chapter and the next such fixatives will be discussed 

 one by one. The various facts that have already been related about 

 them will here be brought together in summary form, and further 

 information will be added so as to afford as many-sided a view of 

 each as possible. Certain important facts about fixation are not 

 well suited to the kind of general treatment adopted in the earlier 

 chapters, but lend themselves to separate exposition under the 

 heads of particular fixatives. 



It is thought that the principles of fixation can be explained 

 better by a fairly full account of a few primary fixatives than by a 

 sketchy one of many. The eight described in these two chapters 

 have been chosen partly because they are components of familiar 

 mixtures, partly because they are diverse in action and illustrate 

 many important points about fixation. The selected primary 

 fixatives are these: — 



coagulant 



ethanol. .... This chapter, p. 92 



picric acid .... ,, p- 96 



mercuric chloride ... ,, P- 99 



chromium trioxide . . „ p. 104 



89 



