PRIMARY fixatives: COAGULANTS 91 



facture than is given in these chapters, see especially Thorpe and 

 Whiteley ^o* and Kirk and Othmer.^e? 



Introduction as fixative. Care has been taken to provide accurate 

 information on this subject. Historical matters are often handled 

 carelessly in scientific works. 



Reactions with proteins. Readers who want further information 

 on this subject, beyond the summaries given here, should turn 

 back to chapters 2 and 3. In the present chapter and the next, 

 brief notes are given under this heading about the effects of fixa- 

 tives on solutions of nucleic acids, because this follows naturally 

 on the discussion of their effects on nucleoproteins. 



Reactions with lipids and Reactions with carbohydrates. The 

 information under these headings is not given in any other part of 

 the book. 



Rate of penetration. The remarks made on this subject in these 

 chapters summarize what has already been said about it in chapters 

 2 and 4; some additional facts are added. The K-values given are 

 based on the following data: — 



25 hours' penetration into gelatine/albumin gel; ^^ 

 12 hours' penetration into mammalian liver; ^°° 

 25 hours' penetration into liver of rabbit. ^^ 



It follows from what has been said in earlier chapters that the 

 K-values would not have differed much if other periods had been 

 chosen. 



It is important for the reader to remember that fixatives pene- 

 trate much faster into gelatine/albumin gel than into liver. Thus 

 a K-value of o-8 is very slow for penetration into the gel, but 

 moderate for penetration into liver. 



Shrinkage or swelling. The figures for the shrinkage or swelling 

 of gelatine/albumin gels represent the volumes after 18 hours' 

 fixation. The results obtained by different authors with different 

 organs and cells are not entirely concordant. The attempt is made 

 to present a general picture of the effect of each fixative in causing 

 change of volume and in leaving the tissues subject to such change 

 on subsequent treatment. For further information on this subject, 

 see pp. 36 and 75. 



Hardening. There is unfortunately no quantitative information 

 beyond the rather meagre data of Wetzel ^^^ (see p. 86). 



Immediate effects on particular constituents of the cell. Under this 

 heading an attempt is made to integrate the results obtained with 



