STAINS AND STAINING 55 



SO weak that the solution has a hght brown color, or fixed in weak os- 

 mic acid, only 4 or 5 drops of 1 per cent osmic acid to 50 c.c. of distilled 

 water, this carmalum is good for material to be mounted whole. Di- 

 lute the stain considerably, put in a crystal of thymol to prevent mold, 

 and allow the stain to act for weeks, or even a couple of months. It is 

 not likely to overstain. 



Alum cochineal. — 



Powdered cochineal 50 g. 



Alum 5 g. 



Distilled water 500 c.c. 



Dissolve the alum in water, add the cochineal, and boil; evaporate 

 down to two-thirds of the original volume, and filter. Add a few drops 

 of carbolic acid to prevent mold (Stirling). 



Stain as with alum carmine. It used to be a common practice to 

 stain in bulk in alum cochineal and counter-stain on the shde with 

 Bismarck brown. 



Balling's iron aceto-carmine 1. — For counting chromosomes in pollen 

 mother-cells mounted whole, Belhng used a modified aceto-carmine 

 method. The preparations are good for an immediate count, but do 

 not last longer than a few days or a week. 



"Ordinary aceto-carmine is prepared by heating a 45 per cent solu- 

 tion of glacial acetic acid to boihng with excess of powdered carmine, 

 cooling, and filtering. The young anthers are teased out with steel 

 blades or needles in a drop of this until it changes slightly toward blu- 

 ish red. An excess of iron spoils the preparation." 



Balling's iron acato-carmine 2. — "To a quantity of aceto-carmine a 

 trace of solution of ferric hydrate dissolved in 45 per cent acetic acid is 

 added until the hquid becomes bluish red, but no visible precipitate 

 forms. An equal amount of ordinary aceto-carmine is then added. 

 The anthers are teased out with nickled instruments." A cover-glass 

 is then added and sealed with vaseline. The preparation lasts only a 

 few days, but is much superior to any obtained by the usual intra 

 vitam processes. 



The method is not as easy as it might seem to be. Much time will be 

 saved by reading the detailed account given in Belling's book, The 

 Use of the Microscope. 



McClintock's iron acato-carmina. — Dr. Barbara McClintock's 

 modification of the Belling method makes the preparations permanent. 



