AND HOW TO USE IT. 241 



cause the haematoxylin to turn red ; for this reason, sections 

 which have been hardened in chromic acid should be placed in a 

 watch-glass, and covered with distilled water, to which add a drop 

 or two of a 40 per cent, solution of caustic potash. Allow it to 

 remain therein 10 or 15 minutes. To use the fluid, add a few 

 drops to an ounce of distilled water, so as to make a pale-violet 

 solution ; allow the sections to remain in this solution from twelve 

 to twenty-four hours. Or, a stronger solution may be employed, 

 which will stain specimens in from ten to thirty minutes, and still 

 give good results. Mount either in glycerine, acetate of potash, 

 balsam, and benzole, or, better, resinous turpentine. 



Eosin Solution, for fresh tissues. — It is usual to have a strong 

 solution of from i to 10 or 20 per cent, on hand. A few drops 

 are then added to a watch-glassful of water or alcohol. It is apt 

 to diffuse, unless special care is taken, and long soaking — say, for 

 twenty-four hours — is practised. Renaut employs either a watery 

 solution alone, or with the admixture of one-third of its volume of 

 alcohol. The sections are then washed in distilled water, and 

 may be preserved in a neutral solution of glycerine, to which i per 

 cent, of chloride of sodium has been added to prevent the 

 glycerine dissolving the eosin. In examining the fixed corpuscles 

 of the subcutaneous tissue, Renaut injects beneath the skin a 

 solution of eosin and water (i to 500), and then removes a 

 portion of the infiltrated tissue with the scissors. Eosin is a 

 phenol dye, and stains epithelium a dark-red, axis cylinders of 

 nerves, colours areolar tissue, nuclei of ganglion cells, and their 

 processes. The amyloid substance in that form of degeneration 

 stains bright red. Fresh tissues are hardened and stained simul- 

 taneously. It is valuable for the recognition of blood corpuscles. 

 The solution is made as follows: — Eosin, i part; alum, i part; 

 alcohol, 200 parts; mix. Gibbes uses 5 grms. of the powder, 

 which should be rubbed up in a mortar, with 100 cc, of distilled 

 water, making a 5 per cent, solution. 



Cochineal Dye. — Take 7 grms. cochineal and 7 grms. alum in 

 powder, rub thoroughly together in a mortar, and add 700 cc. 

 distilled water, evaporate to 400 cc., filter twice, and afterwards 

 add I or 2 drachms of absolute alcohol. 



