ALCOHOLIC COCHINEAL. 109 



OTHER ALCOHOLIC CARMINE STAINS. 



171. Alcoholic Boric Acid Carmine (FRANCOTTE, Bull. Soc. Beige 

 Mic., 1886, p. 48). Carmine, 0'4 grm. ; boric acid, 5 grms. ; water, 25 c.c. ; 

 90 per cent, alcohol, 75 c.c. Boil and filter. 



Dutilleul's Picro-borax-Carmine (Bull. Sci. Dep. Nord, xvi, 1885, 

 p. 371). This is quoted here as having the distinction of being the very 

 worst stain I have ever tried. 



Baumgarten makes a " borax-picro-carmine " by adding crystals of 

 picric acid to Grenadier's solution until it assumes a blood-red colour (Journ. 

 Roy. Mic. Soc., 1888, p. 676 ; 1889, p. 149). 



172. Alcoholic Cochineal (MAYER'S Old Formula, Mitfh. ZooL 

 Stat. Neap., ii, 1881, p. 14). Cochineal in coarse powder is 

 macerated for several days in alcohol of 70 per cent. For 

 each gramme of the cochineal there is required 8 to 10 c.c. of 

 the alcohol. Stir frequently. Filter, and the resulting clear, 

 deep red solution is fit for staining. 



The objects to be stained must previously be imbibed with 

 alcohol of 70 per cent., and alcohol of the same strength must 

 be used for washing out or for diluting the staining solution, 

 as water, or alcohol of a different strength, gives rise to tur- 

 bidity and precipitation of colouring matter (the fluid holding 

 in solution matters that are only soluble in alcohol of exactly 

 that degree of concentration). The washing out must be re- 

 peated with fresh alcohol until the latter takes up no more 

 colour. Warm alcohol acts more rapidly than cold. Over- 

 staining seldom happens ; it may be corrected by means of 

 70 per cent, alcohol, containing y 1 ^- per cent, hydrochloric or 

 1 per cent, acetic acid. 



Small objects and thin sections may be stained in a few 

 minutes, larger animals require hours or days. In the latter 

 case large quantities of the solution must be employed. Very 

 thin sections and delicate objects are best stained in a very 

 dilute solution. 



A nuclear stain, slightly affecting protoplasm. The colour 

 varies with the reaction of the tissues, and the presence or 

 absence of certain salts in them. Crustacea with thick chi- 

 tinous integuments are generally stained red, most other 

 organisms blue. The stain is also often of different colours 

 in different tissue elements of the same preparation. Glands 



