36 CHAPTER IV. 



FOL (Lchrb. d. vergl. milt. Anat., 1884, p. 100) recommends the 

 following variant : 



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



1 per cent, osniic acid . . 2 



2 per cent, acetic acid . . . 5 ,, 

 Water 68 



that is to say, a mixture much 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 CORI (Zeit. iviss. 

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



SECOND or STRONG formula (Zeit. wiss. l\lik., I, 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. I therefore recommend that the osmic 

 and chromic acid be kept ready mixed in the proportions 

 given, and 5 per cent, of acetic acid added at the moment of 

 using. 



WEAKER FORMULA. More recently, FLEMMING has been 

 making up the mixture with only 2 parts of the osmic acid 

 instead of 4, and has spoken of this modification as " weaker 

 osmium mixture" (MEVES, in Encycl. Mikr. Techn., p. 476). 



MEVES (loc. cit.) takes for delicate objects 15 parts of 

 chromic acid of only 0'5 per cent., 2 or 4 of osmic acid of 

 2 per cent., and 1 of acetic acid, and thus gets less 

 shrinkage. 



PODWYSSOZKI recommends (for glands especially) the following modi- 

 fication : 



1 per cent. CrO 3 dissolved in 0'5 per cent, solution of 

 corrosive sublimate . . . . .15 c.c. 



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

 Glacial acetic acid . . . . . 6 to 8 drops. 



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

 is unfavourable to staining (ZiEGLER's Beitrage z. path. Anat., i, 1886 ; 

 Zeit. wiss. Mik., iii, 1886, p. 405). 



The first or weak liquid is the better for very small 

 objects, the second or strong one for larger ones, as it has 

 l> ffi-r ]n> f radon. These liquids may be allowed to act for 

 many liours or days, or according to some workers even 



