110 CARMINE AND COCHINEAL STAINS. 



or their secretion often stain grey-green. In embryos of 

 Lumbricus Kleinenberg found the vessels to stain red, their 

 contents of an intense blue. 



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 ( 575). 

 The acid 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 power 

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

 Arthropoda, whose chitinous investments are but very slightly 

 permeable by aqueous solutions of carmine. 



I have treated this stain at considerable length because I 

 am convinced that it ought to be better known. It is very 

 useful in many cases (Annelids, for instance), and indispen- 

 sable for Arthropoda. On the other hand, it gives a very 

 poor stain with unsuitable objects, and the majority of the 

 objects with which the histologist has to do are in this case. 

 For this reason MAYEK has been led to devise the fluid de- 

 scribed in the following paragraph, which, containing in 

 itself the salts necessary for producing a rich and energetic 

 selectivity of stain, gives good results with all classes of ob- 

 jects. He almost appears to intend it entirely to take the 

 place of the old fluid. But I think the old fluid cannot yet 

 be discarded. It has over the new fluid 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. 



173. MAYER'S Alcoholic Cochineal, New Formula (Mitth. Zool. 

 Stat. Neapel, 10, 3, 1892, p.498). Cochineal, 5 grms.; chloride 

 of calcium, 5 grms. ; chloride of aluminium, 0'5 grm. ; nitric 

 acid of 1'20 sp. gr., 8 drops ; 50 per cent, alcohol, 100 c.c. 

 Powder the cochineal finely and rub up in a mortar with the 

 salts, add the alcohol and acid, heat to boiling-point, leave to 



