CHAPTER 5 



Practical Fixative Solutions 



The only primary fixatives that are commonly used without the 

 admixture of other primaries are formaldehyde and osmium 

 tetroxide. Solutions of primaries used in practice in this way may 

 be called simple fixatives to distinguish them from fixative mix- 

 tures, which contain two or more primaries. Simple fixatives 

 usually contain 'indifferent' or non-fixative salts (p. 29) in addi- 

 tion to the primary. Some of the indiff"erent salts that are used 

 with formaldehyde and osmium tetroxide will be mentioned in 

 the present chapter. 



The great majority of practical fixative solutions are mixtures. 

 The formulae for a very large number of these have been pub- 

 lished. It is evident, from a study of the papers in which the 

 formulae first appeared, that most of them were not the product 

 of scientific experiment based on knowledge of the properties of 

 their components. On the contrary, they were put together in a 

 hit-or-miss fashion. In several cases the formula was relegated to 

 a footnote, with no indication of any reasons governing the 

 choice or concentration of the ingredients. Some of these empiri- 

 cal fluids gave good results and found favour, others did not. A 

 process of natural selection of almost random variations resulted 

 in the survival, on the whole, of the fittest; though many that are 

 used are superfluous. 



To understand the action of fixative mixtures, it is best to make 

 a careful study of a few valuable ones. The principles involved will 

 emerge, and will be found widely applicable. The mixtures chosen 

 for study in this book are those of Clarke, Zenker, Flemming, 

 Helly, and Altmann. 



The reader may care to refer to the general remarks on the 

 period of fixation given on p. 24. 



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