CHROMO-ACETO-OSMIC ACID. 25 



Cellule, 1, 2, 1885, p. 211) has employed a mixture one third stronger in 



osmium and twice as strong in chromic acid, viz. 



Chromic acid of 2 per cent, (or even stronger) . 45 parts. 



Osmic acid of 2 per cent 16 



Glacial acetic acid . . . . 3 ,, 



In the Traite des Muth. Techniques, 1887, I treated tliis 

 formula somewhat coldly, pointing out (what was the case) 

 that Flemming recommended it merely for a very special 

 purpose, the hunting for karyokinetic figures, and that he did 

 not recommend it for general purposes. Further experience 

 has shown that it is applicable to general purposes, and will 

 probably be found for most purposes considerably superior to 

 the weak formula. I should use it by the hogshead if it were 

 not somewhat expensive. 



Arnold, in the place quoted in the last paragraph, says that 

 it is to be avoided if you wish to demonstrate the structure of 

 certain nuclei (of wandering cells) ; and the other objections 

 there quoted as applying to the weak formula are intended to 

 apply more or less to the present formula. It will be well 

 not to attach too much importance to them. Let delicate 

 structures be fixed for twenty-four hours or more, washed in 

 running water for an hour, and in successive alcohols for 

 twenty-four hours, sectioned, and stained with safranin or 

 gentian violet, and there will be little complaint of defective 

 preservation. 



The strong mixture does not brown tissues more than the 

 weak mixture, but rather less. 



Fat is blackened by these mixtures ; but the blackened fat 

 can be entirely dissolved out of the tissues by treating them 

 for a few hours with turpentine that has been exposed to sun- 

 light for an hour or two (see Flemming in Zeit. f. wiss. Mik., 

 vi, 1, 1889, p. 39; and vi, 2, 1889, p. 178). 



PODWYSSOZKI recommends (for glands especially) the following modifi- 

 cation : 



1 per cent. Cro 3 dissolved in 0'5 per cent, solution of corro- 



sive sublimate 15 cc. 



2 per cent, osmium solution. . . . . . 4 cc. 



Glacial acetic acid 6 to 8 drops. 



The sublimate is said to augment the penetration of the osmium, but is 

 unfavorable to staining. The proportion of acetic acid is reduced in order 

 to avoid swelling of the tissue elements (ZIEGLER'S Beitrdge z. path. Anat., 

 i, 1886 ; cf. Zeit.f. wiss. Mik., iii, 3, 1886, p. 405). 



