CARMINE AND COCHINEAL STAINS. 173 



to stand for a week, and then is filtered. If on 

 keeping more carmine is deposited, it must be refiltered. 



Preparations should remain in the stain until they are 

 thoroughly penetrated (for days if necessary), and then be 

 brought (without first washing out) into alcohol (of 70 per cent. ; 

 this is absolutely necessary MAYER) acidulated with 4 to 6 

 drops of hydrochloric acid to each 100 c.c. of alcohol. They 

 are left in this until the stain is differentiated, and may then 

 be washed or hardened in neutral alcohol. Four drops of 

 HC1 is generally enough. Three drops I find not quite 

 sufficient. The stained objects should remain in the acidu- 

 lated alcohol till they acquire a bright transparent look. 

 This may require days (MAYER). 



For delicate objects, and for very impermeable objects, it 

 may be well to increase the proportion of alcohol in the 

 stain ; it may conveniently be raised to about 50 per cent. 

 It should not exceed 60 per cent, in any case (MAYKK). 



This stain is probably by far the most popular of any for 

 staining in bulk. It is easy to use, and gives a most 

 splendid coloration. But it is not so penetrating as is 

 commonly supposed, and has the defect of sometimes form- 

 ing precipitates in the cavities of bulky objects which cannot 

 be removed by washing out. And it must be remembered 

 that the fluid is alkaline, and therefore may not be suitable 

 for delicate cytological work. 



\. MAYER'S Paracarmine (Mitth. Zool. Stat. zu Neap'el, 

 x, 3, 1802, p. 491). Carminic acid, 1 grm. ; chloride of 

 aluminium, 0'5 grm. ; chloride of calcium, 4 grins. ; 70 per 

 cent, alcohol, 100 c.c. Dissolve cold or warm, allow to 

 settle, and filter. A light red liquid, specially adapted for 

 staining in bulk, and much like Grenadier's alcoholic borax- 

 carmine. 



Objects to be stained should not have an alkaline reaction, 

 nor contain any considerable amount of carbonate of lime 

 (spicules or skeletal, parts of corals, etc.) which would give 

 rise to precipitates (MAYER). Wash out sections, or objects 

 intended to be sectioned, with pure 70 per cent, alcohol. 

 Objects intended to be mounted whole may be washed out 

 with a weak solution of aluminium chloride in alcohol, or if 

 this be not sufficient, with 5 per cent, common acetic acid (or 



