142 CARMINE AND COCHINEAL STAINS. 



equal volume of 70 per cent, alcohol, allow it to stand some time and 

 filter. 



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, acidulated with 4 to 6 

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

 in this until they have taken on a bright transparent look (which 

 may require days), and may then be washed or hardened in neutral 

 alcohol. Four drops of HC1 is generally enough. Three drops I 

 find not quite sufficient. 



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 (MAYER). 



This stain used to be 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 forming precipitates in the cavities of bulky objects 

 which cannot be removed by washing out. And the fluid is alkaline, 

 and therefore may not be suitable for certain delicate work. 



234. MAYER'S Paracarmine (Mitth. Zool. Stat. Neapel, x, 3, 1892, 

 p. 491). Carminic acid, 1 grm. ; chloride of aluminium, 0-5 grm. ; 

 chloride of calcium, 4 grms. ; 70 per cent, alcohol, 100 c.c. Dissolve 

 cold or warm, allow to settle, and filter. 



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. 

 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 

 2-5 per cent, glacial acetic acid) in alcohol. This may also be done 

 with section material, if it is desired to obtain a more purely nuclear 

 stain. 



For staining bulky objects with large cavities, such as Salpa, the 

 solution should be diluted (with alcohol) ; and as this may cause 

 precipitates to form during the staining, especially if the objects are 

 not very clean, it is advisable to slightly acidify the dilute solutions. 



Instead of calcium chloride, which is very hygroscopic, strontium 

 chloride may be taken. 



Paracarmine is less hurtful to delicate tissues than borax carmine ; 

 it is more highly alcoholic, therefore more penetrating ; and has less 



