CHAPTER IV. 35 



39. Chromo-acetic Acid (FLEMMING, Zellsbz., Kern. u. Zellth., 

 p. 382). 



Chromic acid . . . 0-2 to 0-25 per cent. 

 Acetic acid . . 0*1 per cent, in water. 



Flemming found this the best reagent for the study of the achromatic 

 elements of karyokinesis. You can stain with hsematoxylin, or the basic 

 anilin dyes. 



The following has been recommended for Annelids by EHLERS : 

 To 100 c.c. of chromic acid of 0-5 to 1 per cent, add from 1 to 5 drops 

 of glacial acetic acid. The acetic acid is said to be sufficient to counter- 

 act any shrinkage due to the chromic acid. Fix overnight, wash out 

 several hours in water. 



Similar to this is the k ' chromo -acetic acid, No. 1," of Lo BIANCO 

 (Mitth. Zool. Stat. Neapel, ix, 1890, p. 443), viz. 1 part 50 per cent, 

 acetic acid and 20 parts 1 per cent, chromic acid, which is found very 

 useful for fixing marine animals. 



40. Chromo-formic Acid (RABL, Morph. Jahrb., x, 1884, pp. 215, 

 216). Four or 5 drops of concentrated formic acid are added to 

 200 c.c. of 0-33 per cent, chromic acid solution. The mixture must 

 be freshly prepared at the instant of using. Fix for twelve to 

 twenty-four hours, wash out with water. Used by Rabl for the 

 study of karyokinesis. 



41. Chromo-aceto-osmic Acid (FLEMMING, Zellsubstanz, Kern und 

 Zetttheilung, 1882, p. 381). FIRST or WEAK formula : 



Chromic acid . . . 0-25 per cent. ) 

 Osmic acid . . . .0-1 ,, - in water. 

 Glacial acetic acid . .0-1 ,, ) 

 MEVES (Encyd. mikr. Techn., 1, p. 475) sometimes adds 1 per cent, 

 of sodium chloride. 



FOL (Lehrb. d. vergl. mik. Anat., 1884, p. 100) recommends the 

 following variant : 



1 per cent, chromic acid . . . .25 vols. 



1 per cent, osmic acid . . . 2 ,, 



2 per cent, acetic acid . . . 5 

 Water 68 



that is to say, a mixture weaker in osmium than Flemming's. 



A mixture still weaker than this in osmium, viz. with 1 vol. osmic 

 acid solution, instead of 2, has been recommended by Com (Zeit. wiss. 

 Mik., vi, 1890, p. 441). 



SECOND or STRONG formula (Zeit. wiss. Mik., 1, 1884, p. 349) : 



1 per cent, chromic acid . . . .15 parts. 



2 per cent, osmic acid . ... . 4 ,, 

 Glacial acetic acid ..... 1 part. 



If this mixture be kept in stock in large quantities, it may go bad, 

 on account of the large proportion of organic acid contained in it. 



32 



