40 CHAPTEE IV. 



ziige) remarks on Pritchard's formula " An altogether silly receipt; after 

 a short time the mixture has lost its acid reaction, and then only the 

 alcohol can act." See also the remarks on the mixture of PEKENYI, 52. 



43. Chromo-acetic Acid (FLEMMING, Zelklz., Kern u. Zellth., 

 p. 382). 



Chromic acid . 0"2 to 0'25 per cent. 



Acetic acid . . O'l per cent., in water. 



Flemniing found this the best reagent for the study of 

 the achromatic elements of karyokinesis. (Flemining wrote 

 this in 1882, and I doubt whether it would now hold good.) 

 Stain with hjBinatoxylin (the preparations are Iwt favourable 

 for staining with safraiiiii or other coal-tar colours). 



The following has been recommended as a good fixing and 

 hardening mixture for Annelids in general, and probably for 

 other forms, by EHLERS (I do not know whether it has been 



J / 



published elsewhere) : 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 

 proportion of acetic acid indicated is said to be sufficient to 

 counteract any tendency to shrinkage due to the chromic 

 acid. 



Similar to this is the " chromo-acetic acid, No. I," of Lo 

 BIANCO (Mittli. ZooL 8 tat. Neapel, is, 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. 



44. Chromo-formic Acid (RABL, Morpli. Jalirl>., x, 1884, 

 pp. 215, 216). Four or five 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. 



45. Chromo-osmic Acid (MAX FLESCH, Arch.f. milt. Anat., xvi, 1879, 

 p. 300). This mixture (osmic acid O'lO, chromic acid 0'25, water lOO'O) 

 may for almost all purposes he considered to he superseded by that of 

 Flemming, 1<>. 



Lo BIANCO (MUth. Zool. Staf. Xt'ttjx'/, ix, 1890, p. 443) 

 employs for marine animals a mixture of 1 part 1 per cent, 

 osmic acid and 50 parts 1 per cent, chromic acid. 



46. Chromo-aceto-osmic Acid (FLEMMING, Zellsubstanz, Kern 

 Zillf/iri/iunj, 1882, p. o81), FIRST or WEAK formula: 



