THE IRON-ACETOCARMINE METHOD OF FIXING 

 AND STAINING CHROMOSOMES. 



JOHN" BELLING, 

 CARNEGIE INSTITUTION OF WASHINGTON. 



A short description of this procedure was given in Vol. 55 of 

 the American Naturalist, pp. 573-574. The method has now 

 been used almost daily for five years, and certain improvements 

 have suggested themselves. 



The solution can be prepared by mixing about equal volumes of 

 glacial acetic acid and water. To this is added powdered carmine 

 In excess. The liquid is then just brought to boil, cooled, and 

 decanted. To the red solution there are then added a few drops 

 of a solution of ferric hydrate in 50 per cent, acetic acid, to act 

 as a mordant. The amount of iron varies with different objects. 

 Too much produces a precipitate in a short time. The more 

 iron, the darker and bluer is the stain. A bluish red is usually 

 the best. Large cover-glasses (20 by 50 mm.) should be used, 

 and they should not be thicker than 0.17 mm. (Small or thick 

 covers prevent pressure being properly applied to individual 

 cells.) There should be a minimum thickness of liquid under 

 the cover-glass. The edges can be sealed with a honey-thick 

 solution of dammar in xylol applied with a brush; or better 

 perhaps, with melted soft paraffin. 



The following varied modes of preparation are useful in 

 different cases. 



1. Pollen-mother-cells, etc., are obtained free by pressing or 

 tapping cut segments of anthers in a drop of iron-acetocarmine. 



2. The cut-up anthers, or minute fragments of animal ovaries 

 or testes, are put in a tube with a large excess of iron-acetocarmine. 

 After 2 to 7 days, preparations are made in the usual way. 

 This gives good results with cancer tumors. 



3. Smears of large anthers or testes are made on a cover-glass, 

 which is then laid on a drop of iron-acetocarmine on a slide. 



4. For staining the vegetative and generative nuclei in pollen- 

 grains or pollen-tubes, etc., crystals of chloral hydrate are dis- 

 solved in a few drops of iron-acetocarmine until the liquid just 



