CHAPTER IV. 31 



soaking, it frequently happens that some of the acid remains in the 

 tissues, and causes them to blacken in time, and in any case hinders 

 staining. To obviate this blackening it has been advised to wash 

 them out in ammonia-carmine or picro-carmine (not very effectual), 

 or to soak them for twenty-four hours in a solution of bichromate 

 of potash (Miiller's solution or Erlicki's will do), or in 0*5 per cent, 

 solution of chromic acid, or in Merkel's solution. The treatment 

 with bichromate solutions has the great advantage of highly facili- 

 tating staining with carmine or hsematoxylin. Max Schultze 

 recommended washing, and mounting permanently in acetate of 

 potash ; Fol, treatment with a weak solution of carbonate of 

 ammonia. But the best plan of all is to properly bleach the prepara- 

 tions. See " Bleaching." This may be done by means of peroxide 

 of hydrogen. OVERTON (Zeit. wiss. Mik., vii, 1890, p. 10) finds that 

 it is completed in a few minutes in a mixture of 1 part commercial 

 peroxide with 10 to 25 parts 70 per cent, alcohol. (The commercial 

 peroxide, slightly acidulated with HC1, will keep well in the dark ; 

 but the mixture with alcohol must be made fresh for use.) Accord- 

 ing to BRISTOL (Amer. Natural, xxvii, 1893, p. 176) the peroxide acts 

 best in the sun. BINET (Journ. de VAnat. et de la Physiol., xxx, 

 1894, p. 449) has successfully used permanganate of potash. MANN 

 (Methods, etc., p. 83) takes a solution of 0-25 per cent., and treats 

 the browned tissues with 1 part of saturated solution of sulphurous 

 acid to 9 of normal salt solution. . . . MONCKEBERG and BETHE 

 (Arch. Mik. Anat., liv, 1899, p. 135) have succeeded in satisfactorily 

 restoring the staining susceptibility of osmium material by means 

 of sulphurous acid (obtained by adding hydrochloric acid to bisul- 

 phite of sodium, 2 to 4 drops of the acid added to 10 c.c. of a 2 per 

 cent, solution of the salt). 



FOL (Lehrb., p. 174) recommends a weak aqueous solution of ferri- 

 cyanide of potassium. 



I find the sulphate of iron solution used in Benda's haematoxylin 

 stain has a marked bleaching effect, and so also, though in a less degree, 

 the iron alum of Heidenhain's process. 



ALTMANN (Die Elementarorganismen, pp. 33 and 35) puts sections 

 overnight into gold chloride of 2 per cent., and reduces in formic acid 

 in the sun, and removes the gold by iodised alcohol. 



But perhaps the best plan is the chlorine method of MAYER, or 

 his magnesium peroxide, for both of which see " Bleaching." 



The same stains recommended for objects fixed by the vapours 

 will be found useful here. For sections, of course, in both cases 

 safranin and other anilin stains may be employed with advantage, 

 as may hsematoxylin. 



