226 THE MICROSCOPE. 



for teasing out ; for hardening they require to be kepi 

 in either Miiller's fluid or chromic acid for a few days, 

 and to complete the process by transferring to alcoho" 

 or methylated spirit for from 12 to 24 hours. Wher 

 employing chromic acid, bichromate of potash o] 

 picric acid, immerse only a small portion of tissue in t 

 large quantity of either fluid, always changing ii 

 in 12 or 24 hours. Osmic acid not only hardens 

 but stains tissues, and sections can be cut without sub. 

 sequent immersion in alcohol. Sections of skin, anc" 

 cornea, can also be made after reduction by th( 

 chloride of gold in acidulated water ; a half per cent 

 of either chloride of gold or of nitrate of silver wil 

 be found strong enough for most purposes. A ] 

 or a 1-|- per cent, of chloride of gold is recommendec 

 for very special specimens. The most commonly usec 

 colour stains are carmine, logwood, picro-carminatc 

 of ammonia (which combines the action of picric anc 

 carmine), hsematoxyline and the aniline colours, a$ 

 magenta, commercially known as roseine or acetate o: 

 rosaline, aniline red, eosin, aniline blue, violet, anc 

 methyl - aniline. Purpurine, a dye extracted fron 

 madder, is also highly spoken of as a stain by Banvier 

 Dr. Thin strongly recommends it. It is prepared foi 

 use as follows: "A solution of 1 part of alum in 20( 

 parts of distilled w r ater is brought to the boiling poin 

 in a porcelain capsule, and a small quantity of solic 

 purpurine rubbed up in a little distilled water is addec 

 to it. The purpurine quickly dissolves, but ther< 

 should remain a small quantity undissolved, which in- 

 dicates that the solution is concentrated. It must b< 

 filtered whilst hot into rectified spirit. The alcoho 

 should constitute a fourth part of the total volume o: 

 the mixture. The fluid obtained is of a beautifu 

 orange red by transmitted light : it is, in fact, fluores- 

 cent. At the end of a month a slight precipitate ii 

 observed, and it begins to lose some of its colouring 

 matter. Tissues should remain in it from twenty-foul 

 to forty-eight hours. Aniline blue-black is strongly 

 recommended for staining the nerve-cells of the braii 

 and spinal cord. 



