144 FIXATION 



considerable proportion of the 27 would almost inevitably have 

 been chosen. The aqueous mixtures are listed in table 8. The two 

 non-aqueous ones are Clarke and Carnoy. 



The dates of introduction of these 27 fixatives have some in- 

 terest from the historical point of view. The dates of invention of 

 two are unknown. The formulae for the remaining 25 were first 

 published in the several decades as follows: — • 



1850-59 I 



1860-69 o 



1 870-79 I 



1880-89 4 



1890-99 6 



1900-09 4 



1910-19 7 



1920-29 2 



If the list of fixative mixtures commonly used today were con- 

 siderably extended, it would probably be found that the great 

 majority of them were invented between 1880 and 1919. The most 

 ancient fixative mixture commonly used today is Clarke (1851).^'-" 



Table 8 gives various kinds of numerical information about the 

 25 aqueous fixatives. It was found impossible to make a direct com- 

 parison between all the fixatives in the table except by relating the 

 amount of each ingredient to that of the only substance that 

 occurs in all: namely, water. The concentrations are therefore 

 expressed as percentages, w/W, except that acetic acid is expressed 

 as v/W, since this substance is nearly always measured by volume 

 in biological laboratories. (See Appendix, p. 313.) 



Bouin's fluid ^^ may be used as an example to explain how the 

 concentrations were calculated. The composition is: — 



formalin . . . . . . 25 ml 



picric acid, sat. aq. . . . . . 75 ml 



glacial acetic acid . . . . . 5 ml 



The approximate composition of the formalin is 10 g of form- 

 aldehyde and 15 g of water. The water in the picric acid solution 

 is very nearly 75 g. The total amount of water may therefore be 

 taken as 15 + 75 = 90 g. Picric acid is soluble at about 1*4% in 

 water: thus there is about 1-05 g in 75 ml of the saturated solution. 

 The composition of the fluid is therefore: — 



