MINERAL ACIDS AND THEIR SALTS 35 



Stain with alum haematoxylin if you wish to stain in toto (staining 

 in this way with other reagents is possible, but difficult). Stain 

 sections with safranin or other basic coal-tar colour, or with iron 

 haematoxylin. 



For fixing with the strong mixture you need only take a bulk 

 of liquid of some four times the volume of the objects (but with 

 the weak mixture the proportion should be increased). Both 

 of them are first-rate fixatives of cellular structures, both as 

 regards their preservation and as regards their optical differentia- 

 tion. But they must be properly used, and not applied to objects 

 for which they are not fitted. For instance, their jiower of pene- 

 tration is extremely had ; they will not fix proj^ierly, even in a 

 loose-celled tissue, through more than a layer of about five cells 

 thick. They are therefore suitable only for very small objects 

 or for very small pieces of tissue, such as suffice for cytological or 

 histological work. As mentioned in § 31 and above, the addition 

 of NaCl to the Flemming does appear to increase the penetration 

 of both this fluid and Champy's mixture. The strong liquid 

 especially has not the character of a general reagent. As a 

 matter of fact it was recommended by Flemming in the first 

 instance merely for a very special purpose, the hunting for karyo- 

 kinetic figures, and not for general purposes. It is still very 

 much used, but in most cases, Bouin's picroformol will do all 

 that it is intended to do, without its disadvantages. 



It may be used for prolonged hardening, e.g. of small pieces of 

 nervous tissue, and is very good for that purpose. 



Fat is blackened (or browned) by it. Chromatin is mordanted 

 by it for the basic anilin dyes, enabling them to give peculiarly 

 sharp and powerful stains. 



48. Osmic Acid and Bichromate. Alt:mann {Die Elementar- 

 organismen, Leipzig, 1890) takes for his " bioblasts " a mixture 

 of equal parts of 5 per cent, solution of bichromate of potash and 

 2 per cent, solution of osmic acid. The bichromate ought not to 

 contain any free chromic acid. Refer to § 694. 



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

 marine animals a mixture of 100 c.c. of 5 per cent, solution of bichro- 

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



HoEHL {Arch. Anat. Phys., Anat. Abtk., 1896, p. 31) recommends 

 a mixture of 80 c.c. of 3 per cent, bichromate, 20 c.c. of 1 per cent, 

 osmic acid, and 2 c.c. of glacial acetic acid. 



Bensley (see Cowdry, "Mitochondrial Constituents," 

 Contrib. Embryol., Carneg. Inst., Washington) uses 2*5 per cent, 

 bichromate. 



Baker and Thomas take equal parts of 3 per cent, bichromate 

 and 2 per cent, osmium. See " Cytological Technique " (Baker). 



49. Bichromate-chromic-osmic Acid. Champy {Arch, de Zool. 

 Exper., 1913). Mixture of 7 parts of 3 per cent, bichromate of 



2—2 



