HISTOLOGICAL METHODS. 173 



320. Carmine is, however, a somewhat uncertain dye, 

 and it is often difficult to get good results, especially with 

 tissues hardened in chromic acid. This substance, together 

 with picric acid, potassium bichromate, and Mliller's fluid, 

 must always be removed by washing in water previous to 

 staining. 



321. After staining, the superfluous pigment is removed 

 by washing in water acidulated with i per cent hydro- 

 chloric or glacial acetic acid, or in rectified spirit 60 parts, 

 water 39 parts, hydrochloric acid i part (Prit chard]. The 

 acid brightens the colour. 



Tissues stained with carmine may be mounted in Far- 

 rants' solution, glycerine, or dammar. 



322. Picro- carmine. The picro-carminate of am- 

 monia introduced by Schwarz and Ranvier, is an excellent 

 staining agent, and is prepared thus : Take looCC of a 

 saturated solution of picric acid. Prepare an ammoniacal 

 solution of carmine by dissolving i gramme in a few CC 

 water, with the aid of an excess of ammonia and heat. 

 Boil the picric acid solution on a sand-bath, and when boil- 

 ing add the carmine solution. Evaporate the mixture to 

 dryness. Dissolve the residue in looCC water, and filter. 

 A clear solution ought to be obtained ; if not, add some 

 more ammonia, evaporate, and then dissolve as before. 



A double staining is produced. Nuclei are stained by 

 the carmine, while the picric acid gives a yellowish tinge to 

 muscle, epithelium, and epidermis, etc. Sections of skin 

 may be beautifully stained by this fluid : the epidermis, 

 hair, and muscles of the hair follicles are rendered yellow, 

 while the cutis vera is reddened. If carmine staining 

 alone be desired, the stained tissues are placed in dis- 

 tilled water, by which the yellow colour from the picric 

 acid is speedily removed. 



323. Logwood is, like carmine, suitable for staining 

 tissues for permanent preparations. Generally speaking, it 

 stains the same tissue elements as carmine. The tint is 

 violet, and on this account it is not nearly so fatiguing to the 

 eye as a red dye. The tissues may either be fresh, or they 

 may have been hardened in chromic acid or alcohol. It 



