10 MATERIALS AND PROCESSES OF SLIDE-MAKING 



This must be made up immediately before use, or one may prepare it as 

 two solutions, keeping the formaldehyde separate from the chromic acid. 



Mercuric Fixatives. Mercuric chloride is often used as the m_ain protein 

 precipitant in a fixative, as well as in combination with dichromate. It has the 

 very grave disadvantage that steel instruments are destroyed instantly on con- 

 tact with the solutions, so that one must use glass or plastic in handling 

 specimens. There are, however, a number of excellent formulae. One of the 

 best general-purpose fixatives ever invented is: 



Gilson's Fluid: 



Water 88 ml. 



95% Alcohol 10 ml. 



Mercuric chloride 2 Gm. 



Glacial acetic acid 0.4 ml. 



Nitric acid 1.8 ml. 



This is a magnificent fixative for all general zoological uses. Objects may be 

 left in it for many months without becoming unduly hardened, while small 

 objects will be found to be adequately fixed after only a few hours. The fix- 

 ative should be washed out very thoroughly in 70 per cent alcohol before sub- 

 sequent manipulations are undertaken. To the beginning student, seeking a 

 general-purpose fixative, this medium is to be recommended above all others. 

 It occasionally happens that the microscopist desires to fix something which 

 is covered in a very hard shell and, therefore, requires a fixative in which other 

 desirable qualities have to be sacrificed in favor of extremely rapid penetration. 

 One of the best of these mixtures is: 

 Carnoy and Lebrun's Fluid: 



Absolute alcohol 33 ml. 



Glacial acetic acid 33 ml. 



Chloroform 33 ml. 



Mercuric chloride to sat. (about 25 Gm.) 



This fluid may be used equally well with a hard-shelled arthropod or with a 

 hard-shelled seed and will penetrate rapidly enough to preserve the whole. It 

 cannot be used satisfactorily with any object containing fat, which will be 

 dissolved, and is usually employed only when the principal interest of the 

 worker is in nuclear fixation. 



Picric-acid Fixatives. Picric acid (actually trinitrophenol) has been widely 

 used in the last quarter century as a component of fixatives. The best known 

 formula undoubtedly is: 



Bouin's Fluid: 



Saturated aqueous solution of picric acid 75 ml. 

 40% Formaldehyde 25 ml. 



Glacial acetic acid 5 ml. 



