AOETO-CARMINE. 101 



double stain (resting chromatin and nucleoli purple, kinetic 

 chromatin red, the rest brown) . I find it valuable tor staining 

 soft tissues in the mass. As the staining bath contains but 

 very little alum, it may be used with calcareous structures, 

 and is, indeed, for such objects as Pluteus about the best stain 

 that I know of. It is difficult to understand why this admir- 

 able method has not been more used. 



156. Acetic Acid Alum- Carmine (HENNEGUY, Traite des Meth. 

 techn.j LEE et HENNEGUY, p. 88). Excess of carmine is boiled 

 in saturated solution of potash alum. After cooling add 10 

 per cent, of glacial acetic acid, and leave to settle for some 

 days. The deposit of carmine and alum that forms during 

 that time is removed by filtration. 



For staining, enough of the solution is added to distilled 

 water to give it a deep rose tint. Stain for twenty-four to 

 forty-eight hours, and wash for an hour or two in distilled 

 water. (It is important that the water should be distilled in 

 order to avoid the formation of crystals.) Dehydrate with 

 alcohol and mount in balsam. You can mount in glycerin, 

 but the preparations do not keep so well as in balsam. 



The advantage of this carmine is that it has great power 

 of penetration, and stains deep-seated layers of tissue just as 

 well as the superficial ones. The colour of the stain is a some- 

 what inelegant violet, but this can be changed to a warmer 

 tone by treating the objects with dilute HC1, as for borax- 

 carmine objects. 



157. Alum-Carmine and Picric Acid. Alum-carmine objects 

 may be double-stained with picric acid. LEGAL (Morph. 

 Jahrb., viii, p. 353) combines the two stains by mixing ten vols. 

 of alum-carmine with one of saturated picric acid solution. 



GILSON'S picro-alum-carmine (the stain mentioned by BOL- 

 sius in La Cellule, vii, 1, 1891, p. 6, kindly communicated by 

 Prof. G-ILSON) is made by boiling 10 per cent, of cochineal for 

 about twenty hours in saturated solution of alum (in a Lie- 

 big's refrigerator or some flow-back arrangement for prevent- 

 ing diminution of volume by evaporation), and adding 10 per 

 cent, of saturated solution of picric acid. 



158. Aceto-Carmine (Acetic Acid Carmine) (SCHNEIDER'S for- 

 mula, Zool. Anzeig., No. 56, 1880, p. 254). To boiling acetic 



