44 CHAPTER IV. 



tissues are more difficult to stain, but afford, when obtained, 

 a more delicate and selective stain, especially showing up 

 karyokinetic figures and nucleoli. 



The strong formula was recommended by FLEMMING in the 

 first instance merely for a very special purpose, the hunting 

 for karyokinetic figures, and not for general purposes. 

 Further experience has shown that it is applicable to other 

 cytological purposes, and is in many cases considerably 

 superior to the weak formula. But it is not suited to all 

 objects, and FLEMMING has himself pointed out that some 

 workers have used it for purposes for which it is not fitted. 

 It is indeed, I think, even less of a general reagent than the 

 weak formula, though unsurpassed in its own peculiar 

 sphere. 



The strong mixture does not brown tissues more than the 

 weak mixture, but rather less. 



Fat is blackened by both these mixtures. See 39. 



48. Osmic Acid and Bichromate. ALTMANN (Die Elementarorgan- 

 ismen, Leipzig, 1890; Zeit.f. wiss. Mik., vii, 2, 1890, p. 199) recommends 

 a mixture of equal parts of 5 per cent, solution of bichromate of potash 

 and 2 per cent, solution of osmic acid for the demonstration of his granula. 

 The bichromate, he says, ought not to contain any free chromic acid, and the 

 mixture is best prepared freshly when required. 



Lo BIANCO (Mitth. Zool. Stat. Neapel, ix, 1890, p. 443) employs for marine 

 animals a mixture of 100 c.c.of 5 percent, solution of bichromate and 2 c.c. 

 of 1 per cent, osmic acid. 



Evidently, I think, the addition of acetic acid to either of 

 these mixtures is in most cases indicated. This step has, in 

 fact, been taken by HOE.HL (Arch. f. Anat. u. Phys., Anat. 

 Abth., 1896, p. 31 ; Zeit. f. wiss. Mik., xiii, 2, 1896, p. 227), 

 who recommends a mixture of 80 c.c. of 3 per cent, bichro- 

 mate, 20 c.c. of 1 per cent, osmic acid, and 2 c.c. of glacial 

 acetic acid. 



49. Osmic, Bichromate, and Platinic Mixture (LINDSAY 

 JOHNSON'S Mixture). Latest formula, 1895, communicated 

 by Dr. Lindsay Johnson : 



Bichromate of potash (2*5 per cent.) . 70 parts. 



Osmic acid (2 per cent.) . . . 10 ,, 



Platinic chloride (1 per cent.) . 15 ,, 



Acetic or formic acid 5 



