ALCOHOLIC COCHINEAL. 91 



CHAPTER XI. 

 COCHINEAL, HJ:MATOXYLIN, AND OTHER ORGANIC STAINS. 



A. COCHINEAL. 



167. The Use of Cochineal. What is the use of cochineal ? 

 In the first place, it gives us the means of getting a direct 

 nuclear stain by means of an alcoholic solution. For some 

 purposes, this stain is unrivalled. In the second place, it 

 gives us an aqueous stain that takes the place of alum- 

 carmine, with "perhaps a greater richness of differentiation. 



168. Alcoholic Cochineal (MAYEK'S Mitth. 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^th 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 



