CARMINE AND COCHINEAL STAINS. 175 



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

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

 The washing out must be repeated with fresh alcohol until 

 the latter takes up no more colour. Warm alcohol acts 

 more rapidly than cold. Overstaining seldom happens ; it 

 may be corrected by means of 70 per ceot alcohol, contain- 

 ing 3*3- 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. 



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 

 chitinous 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 

 or their secretion often stain grey- green. 



Acids lighten the stain and make it yellowish red. 

 Caustic alkalies turn it to a deep purple. 



The best stains are obtained in the case of objects that 

 have been prepared with chromic or picric acid combinations, 

 or with absolute alcohol. Osmic acid preparations stain 

 very weakly unless they have been previously bleached. All 

 acids must be carefully washed out before staining, or a 

 diffuse stain will result. The stain is permanent in oil of 

 cloves and balsam. 



The object for which this stain was imagined is to obtain 

 an alcoholic staining fluid whose high penetrating pewer 

 allows it to be employed in the case of organisms, such as 

 Arthropoda, whose chitinous investments are but very slightly 

 permeable by aqueous solutions. 



This fine stain has over the new fluid (next ) the (for 

 some cases considerable) advantage of being more highly 

 alcoholic ; and it does not contain free acid, so that it can be 

 used with calcareous structures which it is wished to preserve 

 which the new fluid cannot. For specimens of Pluteus, 

 for instance, I find it excellent. 



231. MAYEB'S Alcoholic Cochineal, New Formula (Mitth. Zool. 

 Stat. Neapel, x, 3, 1892, p. 498). Cochineal, 5 grms. ; chloride of calcium, 

 o grms.; chloride of aluminium, O'o grm. ; nitric acid of 1 P 20 sp. gr., 8 

 drops ; 50 per cent, alcohol, 100 c.c. Powder the cochineal finely and rub 



