CH. IX] PREPARATION OF REAGENTS 281 



hot in a water bath and then heat the funnel occasionally with a Bunsen flame. 

 The warmer the room the easier to filter paraffin. 



Filter the paraffin into small porcelain pitchers. If the paraffin oven has 

 a compartment large enough, it is well to keep one of the pitchers in the oven, 

 then the paraffin remains melted and is ready for use at any time. 



I 423. Picric-Alcohol. — This is an excellent hardener and fixer for almost 

 all tissues and organs. It is composed of 500 cc. of water and 500 cc. of 95% 

 alcohol, to which 2 grams of picric acid have been added. (It is a \% solution 

 of picric acid in 50% alcohol). It acts quickly, in from one to three days. 

 (Proc. Amer. Micr. Soc, Vol. XII, (1890), pp. 120-122). 



§424. Picro-Fuchsin. — 10 cc. of a 1% aqueous solution of acid fuchsin ; 

 75 cc. of a saturated aqueous solution of picric acid. Stain deeply with hema- 

 toxylin first, then use the picro-fuchsin. Wash off the picro-fuchsin with dis- 

 tilled water. Mount in non-neutralized balsam or better in acid balsam 

 (Balsam 50 cc. glacial acetic acid 5 drops). If the white connective tissue is 

 not red enough increase the amount of acid fuchsin. 



§ 425. Shellac Cement. — Shellac cement for sealing preparations and for 

 making shallow cells is prepared by adding scale or bleached shellac to 95% 

 alcohol. The bottle should be filled about half full of dry shellac then enough 

 959-6 alcohol added to fill the bottle nearly full. The bottle is shaken occa- 

 sionally and then allowed to stand until a clear stratum of liquid appears on 

 the top. This clear, supernatant liquid is then filtered through filter paper or 

 absorbent cotton, using a paper funnel (? 358), into an open dish or a wide- 

 mouth bottle. To every 100 cc. of filtered shellac 2 cc. of Venetian turpen- 

 tine may be added to render it less brittle. The filtered shellac will be too 

 thin, and must be allowed to evaporate till it is of the consistency of thin 

 syrup. It is then put into a capped bottle, and for use, into a small spirit 

 lamp (Fig. 203). In case the cement gets too thick add a small amount of 

 95% alcohol or some thin shellac. The solution of shellac almost always re- 

 mains muddy, and in most cases it takes a long time for the flocculent sub- 

 stance to settle. One can quickly obtain a clear solution as follows : When 

 the shellac has had time to thoroughly dissolve, i. e. , in a week or two in a 

 warm place, or in less time if the bottle is frequently shaken, a part of the dis- 

 solved shellac is poured into a bottle and about one-fourth as much gasolin or 

 benzin added and the two well shaken. After twenty-four hours or so the 

 flocculent, undissolved substance will separate from the shellac solution and 

 rise with the gasolin to the top. The clear solution may then be siphoned off 

 or drawn off from the bottom if one has an aspirating bottle. (R. Hitchcock, 

 Amer. Monthly Micr. Jour., July, 1884, p. 131). 



If one desires to color the shellac, the addition of a strong alcoholic solu- 

 tion of some of the coal tar colors is good, but is liable to dissolve in the 

 mounting medium when shellac is used for sealing, A small amount of lamp- 

 black well rubbed up in very thin shellac and filtered, is good to darken the 

 shellac. 



\ 426. Silvering. — Intercellular substance stains brown or black with 

 nitrate of silver. Use % or %% aq. sol. on fresh tissue. Stain in the silver 



