STAINING FLUIDS. 229 



colour. Stain the tissue in an alcoholic solution of 

 eosin, which will colour it very rapidly, usually in a few 

 seconds. Wash the section thoroughly in water acidu- 

 lated with acetic or hydrochloric acid, a 1 per cent, solu- 

 tion, and stain with iodine green. This will double stain 

 bone and cerebellum ; but if logwood is substituted 

 for the latter, the cerebrum and general substance 

 become stained by the eosin, while the logwood 

 colours the nerve-cells a lilac. 



Gold Chloride and Aniline Dyes. The tissue must 

 be impregnated with chloride of gold, and then stained 

 with either aniline blue, iodine green, or rosein. The 

 tail of a young rat, containing as it does so many dif- 

 ferent structures, is an excellent material for experi- 

 menting upon. Remove the skin from the tail, and 

 place pieces half an inch long into the juice of a fresh 

 lemon for five minutes, wash it to get rid of the acid. 

 The fine tendons swell up under the action of the lemon 

 acid, and permit of the more ready action of the 

 chloride of gold solution. Place the piece for an hour 

 or more in a 1 per cent, solution of gold, remove it 

 and wash it thoroughly, and then place it in a 25 per 

 cent, solution of formic acid for twenty-four hours. 

 This reduces the gold : during the process of reduction 

 the preparation must be kept in the dark. The osseous 

 portion has then to be decalcified in the ordinary way, 

 with a mixture of chromic and nitric acid. After 

 decalcification preserve the whole in alcohol. Transverse 

 sections of the decalcified tail are made, and may be 

 stained with a red dye, as rosein, and afterwards with a 

 watery solution of iodine green. Mounted in dammar. 



Dr. Taffani found that solutions of aniline blue 

 and picric acid produce beautiful green- coloured 

 preparations of the lymphatics, spinal cord, &c. 

 The action of picric acid is not like that of chromic 

 acid, which enters into combination with the sub- 

 stances upon which it reacts, and which, after being 

 hardened, will often part with all colour by repeated 

 washings. The action of picric acid is decidedly less 

 detrimental to most tissues than chromic acid. 



Dr. Seiler uses by preference the simple carmine 



