92 



to a certain extent the advantages of picric acid and mercuric chlorid. A 

 stronger percentage of acetic acid (4 or 5%) is to be preferred with organs con- 

 taining a large amount of connective tissue. 



Fix the object for 1-24 hours ; place in 67% alcohol for 1-2 days, 82% alco- 

 hol for several days, changing several times, whenever the alcohol has become 

 colored yellow. The tissue should be left in the 82% alcohol until almost all 

 the picric acid has been washed out and the alcohol no longer becomes colored, 

 or but slightly. Tincture of iodin may be used as with mercuric chlorid 

 tissue, but is not necessary. Stain as you like. 



§28. Zenker's fluid. Formula: Potassium dichromate, 2.5 gr. ; sodium 

 sulphate, 1 gram ; mercuric chlorid, .5 gr. ; water, 100 c. c. ; and add before 

 using, glacial acetic acid, 5 c. c. This is a fluid used quite generally of late. 

 The potassium dichromate seems to check the brittleness that the mercuric 

 chlorid would cause, otherwise its advantages and faults are those of mercuric 

 chlorid ; staining after it, however, is apt to be a little more difficult and not 

 as brilliant as with mercuric chlorid fixation. Its penetration is surprisingly 

 good. 



Fix in Zenker's fluid 12-48 hours, wash well in water, running or fre- 

 quently changed, 12-48 hours, to remove the dichromate ; transfer to 67% alco- 

 hol for 1-2 days, 82% alcohol for several days, keeping in the dark while in 

 the alcohol. To the 82% alcohol add a drop or so of tincture of iodin, adding 

 fresh iodin or changing the alcohol when the color is lost. This should be 

 continued as long as the iodinized alcohol is decolorized in order to avoid a 

 precipitate of the mercuric chlorid in the tissue. Avoid, however, adding an 

 excess of iodin, since it will affect the s taining quality of the tissue. Stain as 

 you wish. 



§29. Miiller's fluid, /^orma/a .- Potassium dichromate, 2.5 grams ; sodium 

 sulphate, i gram ; water, 100 c.c. This fluid is more of a hardener than a fixer ; 

 it should be avoided (as likewise Eriicki's fluid and potassium dichromate) 

 when the preservation of nuclear structure is desired. Staining after its use is 

 sometimes difficult. It is, however, useful for general work. 



Place the object in an abundance of the fluid and harden for from 1-8 

 weeks, changing the fluid at first each day. In general, 10-14 days will be suf- 

 ficient. Wash in running water for 24-48 hours or longer, remove to 67% alco- 

 hol for 1-2 days, ?>2% alcohol several days. Keep in the dark while in the alco- 

 hols, and change to fresh when the fluid is colored yellow. Tissue hardened 

 in Miiller's fluid cuts well, and it is useful in preparing sections of large organs, 

 or organs with much connective tissue. 



() 30. Eriicki's fluid. Formula : Potassum dichromate, 2.5 grams ; copper 

 sulphate, i gram ; water, 100 c.c. This is quite similar to Miiller's fluid in its 

 action and results, save that its action is more rapid and stronger. Therefore, 

 it had better be employed with smaller objects, and allowed to act only 2-14 

 days. Otherwise, employ like Miiller's fluid. 



\ 31. Potassium dichromate. 2%, 3%, and 5% aqueous solutions. 



