FIXATIVE MIXTURES I41 



fluid, as usually used, is a valuable fixative for the study of chromo- 

 somes and for the detailed histology of very small pieces ; those of 

 Benda and Lewitsky are quite different in character, being in- 

 tended for work on cytoplasmic inclusions, and should be called 

 by the names of the men who introduced them. 



Fixative mixtures are not always ascribed to their actual in- 

 ventors. Thus Clarke ^^'^ introduced in 1851 a mixture of one vol- 

 ume of acetic acid with three of spirits of wine ; in this he soaked 

 tissues that had already been immersed in spirits of wine alone. 

 This mixture was widely used as a direct fixative in the following 

 years, by Beale ^^ and others. Frey ^"^ quoted it in his well- 

 known text-book in 1863, giving die Clarke' sche Vorschrift as 

 3 Theile Alkohol niit i Theil Essigsdure. He continued to quote it 

 repeatedly in his various editions. ^"^ It is therefore rather strange 

 that the mixture should nowadays be almost invariably attributed 

 to Carnoy,^^^ who gave this formula in 1886. It will here be called 

 by Clarke's name, while Carnoy's will stand for the fluid of his 

 own invention ^^^ (absolute ethanol, glacial acetic acid, and 

 chloroform in the proportion of 6 : i : 3 by volume). It may be 

 remarked that Clarke is the better fixative for routine paraffin 

 sections: it falls in grade I, Carnoy in grade II. 



Several authors have mixed a saturated solution of mercuric 

 chloride with glacial acetic acid, but it does not seem possible to 

 find out who first used the familiar mixture of the two substances 

 in the proportion of 95 : 5 by volume. This fluid (here called 

 mercuric/acetic) is useful in zoology, particularly in the preparation 

 of whole mounts. 



Another anonymous mixture is Zenker without acetic. The fluid 

 is radically different from Zenker, because the pH lies on the 

 opposite side of the critical range (p. 132), and proteins therefore 

 react to the chrome anions in it in an entirely different way. This 

 is the only fixative that is useful in cytoplasmic cytology and at the 

 same time good enough for routine histology to reach grade I. 

 Bensley ^^ has recommended a fluid closely similar to Zenker 

 without acetic, but not identical with it. 



For the purpose of generalization it is necessary to choose a 

 limited number of representative fluids. Twenty-five aqueous 

 fixative mixtures have been selected for this purpose, and two not 

 containing water. They are a typical selection of mixtures that are 

 widely used in micro-anatomy, embryology, histology, and cyto- 

 logy. Different authors would have made different lists, but a 



