13 



A delicate fixer useful in some cell work and with small objects. The formalin 

 may be omitted (Picro-acetic). 



Fix 3 to 24 hours, transfer to 67% alcohol, 1 day, 82% alcohol several days 

 changing the fluid frequently as it becomes yellow. Leave in the alcohol until 

 the picric acid has been well washed out. 



18. Hermann's fluid. Formula: 1% aq. sol. platinic chlorid, 15 parts; 

 2% aq. sol. osmic acid, 4 parts; glacial acetic acid, 1 part; or you may take 

 10% % aq. sol. platinic chlorid, 3 parts; 1% aq. sol. osmic acid, 16 parts; glacial 

 acetic acid, 2 parts; water, 19 parts. This is generally recognized as one of the 

 finest fixers known, and it is also the most expensive. The form and structure 

 of cells are well preserved. It should only be employed, however, with very 

 small pieces of tissue, and is to be used especially when cell structure is to be 

 studied. Fat and the myelin of nerve fibers are stained black. 



Fix in this 1 to 24 hours (or longer days or weeks are used by some), wash 

 well in water (running or frequently changed) 2 to 24 hours, and then place 

 in 67% and 82% alcohols, 12 to 24 hours in each. In using this fluid, the smaller 

 the pieces taken the better the fixation will be, and in order that it be possible 

 to obtain a good stain afterwards tissue should not be over-fixed and the fixer 

 should be thoroughly washed out. If there is a blackening of the tissue, or a 

 precipitate in it, both may be removed by treatment of the sections on the slide 

 with a 10 or 20% solution of hydrogen dioxid in 67% alcohol, or with perhydrol 

 (Merck). Employ after Hermann's fluid, as stains, Heidenhain's iron hema- 

 toxylin, Delafield's hematoxylin, safranin (as a red stain), or gentian violet (as a 

 blue stain), or neutral stains. 



19. Flemming's fluid (Chrome-aceto-osmic) . Formula: 1% aq. sol. 

 chromic acid, 15 parts; 2% aq. sol. osmic acid, 4 parts; glacial acetic acid, 

 1 part; or, 10% aq. sol. chromic acid, 3 parts; 1% osmic acid, 16 parts; glacial 

 acetic acid 2 parts; water, 19 parts. This is a fine fixer and in most cases gives 

 as good results as Hermann's, and is not as expensive. It browns tissue less, 

 and while it blackens fat, does not blacken the myelin of myelinic nerve fibers 

 as does Hermann's. It should be employed in general in the same cases and in 

 the same way as Hermann's fluid, and is especially useful in the preservation of 

 free fats and lipoids ( 227) . The presence of chromic acid gives it a distinct value 

 as a cytoplasmic fixer. 



Fix tissue 1 to 24 hours (or longer); wash well in running water 2 to 24 

 hours; place in 67% and 82% alcohols, 12 to 24 hours in each. Bleaching of 

 the sections may be necessary, as with Hermann's fluid. Take only very small 

 pieces of tissue. Employ the same stains as with Hermann's fluid. 



The reduction of the acetic acid to 3 or 4 drops (about TJT%) is advisable when 

 cytoplasmic granules of lipoid composition ( 178) are to be preserved. The fluid 

 may then be spoken of as Benda's fluid. 



20. Mercuro-nitric (Gilson's fluid, modified). Formula: Nitric acid (46, 

 sp. gr. 1.456, 80%), 15 c. c.; Glacial acetic acid, 4 c. c.; Mercuric chlorid, 20 grms.; 

 95% alcohol, 60 c. c.; distilled water, 920 c. c. A good fixer, especially useful 

 where rapid penetration is a factor, and as a fixer of cells rich in yolk (amphibian 

 ova, etc.). 



Fix 12 to 24 hours, transfer to 50, 67, and 82% alcohols. lodin should be 

 used to ensure the removal of all the mercuric chlorid (see 11). 



