378 SOME HARDENING AGENTS. 



Pacini's Fluid.— 



Bichloride of Mercury ... ... i part. 



Common Salt ... • ... ... 2 — 4 parts. 



Water ... ... ... ... 200 parts. 



When 2 parts of salt are used, this formula is very useful as a 

 general preservative, but especially is it useful for blood-corpuscles 

 of cold-blooded animals, as it has a less density than the formula 

 with four parts of salt, which is better for the blood of warm- 

 blooded animals. It preserves spermatic fluid, epithelial cells, 

 nerves, muscle fibres, and fixes infusoria by adding a small quan- 

 tity to the water containing them. 



Pacini's Preservative Fluid for all delicate tissues is made by 

 Corrosive Sublimate ... ... i part. 



Sodium Chloride ... ... 2 parts. 



Glycerine (25 per cent. Baume) -.. 13 parts. 



Water ... ... ... ... 113 parts. 



Allow the mixture to stand undisturbed for at least two months. 

 Then take for use one part, mix with three parts of water, and 

 filter. 



Perenyi's Fluid.— 



Nitric Acid (10 per cent, solution) ... 4 parts. 



Chromic Acid (o"5 per cent, solution) . 3 parts. 



Alcohol ... ... ... •••3 parts. 



Mix. Immerse the specimens for four to five hours ; then use 

 gradual strengths of alcohol, 70 per cent, for twenty-four hours ; 

 strong alcohol for several days ; then absolute alcohol for four to 

 five days ; then cut. The advantages are that segmentation 

 spheres and nuclei are fixed perfectly, ova do not get porous, but 

 cut well, and the stain can be combined with the fixative. In the 

 case of ova, the albuminous envelope must be removed. It is 

 also excellent for dental histology, particularly development. 



Picro-sulphuric Acid — either Kleinenberg's or, better, Mayer's 

 formula — are very good, the latter saving the waste of the picric 

 acid. Always use a large quantity of the solution, and change as 

 often as it is cloudy. It hardens very rapidly (four hours is usually 

 enough), and then wash in 70 per cent, alcohol ; warm alcohol 

 extracts the acid more quickly than cold. Remember 7iever to 



