398 GENERAL MICROSCOPIC TECHNIQUE. 



Picro-carmine (Weigert). Two grammes of carmine mixed 

 with 4 cc. of ammonia are allowed to stand in a tightly closed 

 vessel for twenty-four hours ; 200 grammes of aqueous solution 

 of picric acid are added. After twenty-four hours the addition 

 of a few drops of concentrated acetic acid is made. This pn> 

 duces a precipitate, which after twenty-four hours is filtered out. 



Picric acid also may be used as a counter-stain with sec- 

 tions which previously have been stained with carmine, hsema- 

 toxylin, safranin, or acid fuchsin. For this a dilute alcoholic 

 solution is employed. 



Biondi-Ehrlictis Triple Stain (Methyl-green. Acid Fuchsin, 

 Orange- G). Heidenhain's modification of this stain is made 

 as follows: Saturated aqueojus 2 solutions of the three stains are 

 prepared i.^e., 20 grammes of acid rubin in 100 cc. of water ; 

 8 grammes 01 orange-G in 100 cc. of water; 8 grammes ^of 

 methyl-green 00 in 100 cc. of water. Of these solutions, one 

 mixes 4 cc. of the first with 7 cc. of the second, and then adds 

 8 cc. of the third. They should be added in this order, or a 

 precipitate will result. For staining, 1 cc. of this mixture is 

 diluted with 100 cc. of water. According fo Heidenhain, it is 

 of advantage to add the stain drop by drop to verv dilute 

 acetic acid (1 : 500 water), stirring constantly until the color is 

 bright red. With this stain, it is best to use thin sections of 

 tissue which have been hardened in corrosive sublimate. After 

 stained for twenty-four hours the sections should be 

 washed in 90 per cent, 'alcohol or a mixture of 100 cc. of 

 alcohol and from 2 to 4 drops of acetic acid. 



Many other stains can be used with good results (c. g., van 

 Gieson's fluid (acid fuchsin and picric acid), methylene-blue, 

 nigrosin, orcein, etc.). 



After being stained, sections, whether cut in celloidin or par- 

 affin, are submitted to a treatment which allows them to be 

 mounted on a slide in a medium which is transparent and has a 

 refractive index approaching that of glass (e. <?., Canada balsam). 

 The sections are transferred from the staining fluids to water 

 or a differentiating fluid, in which all excess of stain is washed 



