CHAPTER 3 



Coagulant Primary Fixatives 



In this chapter and the next each of the selected primary fixatives 

 (p. 17) will be considered separately. Its properties will be sum- 

 marized in a systematic way. The intention is to give as complete 

 a summary of the fixative action of each substance as is possible 

 in the present state of knowledge. The information will include 

 a good deal that has been scattered through chapter 2. 



Since the present chapter and the next are likely to be used for 

 reference by some who have not read the earlier part of the book, 

 it is necessary to explain once more what is meant by 'standard 

 concentration'. This is a fixed concentration, approximately that 

 at which the substance in question is commonly used in fixation. 

 Throughout this book, except where the contrary is stated, every 

 remark about the action of a primary fixative refers to its action 

 at (or very near) its standard concentration. 



The expressions w/v, w/w, &c. are defined on p. xv. 



The oxidation-potentials (o.p.) quoted in chapters 3 and 4 are 

 taken from Casselman.^^- ^^ The Z^-values given in these chapters 

 refer to the rate of penetration into gelatine-albumin gel (p. 22), 

 or, in the case of acetic acid, into gelatine-nucleoprotein gel. 



Fixatives that stabilize the proteins of the cell quite well may 

 leave much to be desired where cell-aggregates are concerned, for 

 these may be distorted during fixation or embedding, in such a 

 way as to leave artificial spaces. Groups of cells may become 

 separated from other groups or from basement membranes or 

 connective tissue. Although this book is primarily concerned with 

 cvtology, yet the needs of the histologist and microscopical 

 anatomist must be kept in mind, and the eff'ects of the selected 

 primary fixatives on cell-aggregates will therefore be briefly noted. 



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