158 CHAPTER XIII. 



obtained. These aliow a very intense and highly differen- 

 tiated stain of nuclear structures, cytoplasmic structures 

 being pale. If the baths in the iron and in the stain have 

 been prolonged (twelve to eighteen hours), and the sub- 

 sequent differentiation in the second iron bath also duly 

 prolonged, black preparations will result. These show 

 chromosomes stained, central corpuscles stained intensely 

 black, cytoplasm sometimes colourless, sometimes grey, in 

 which case achromatic spindle-fibres and cell-plates are 

 stained, connective-tissue fibres black, red blood-corpuscles 

 black, micro-organisms sharply stained, sti'iated muscle very 

 finely shown. 



Later {Zeit. wiss. Mik., xiii, 1896, p. 186) Heidenhain gives 

 further instructions for the employment of this stain in the 

 study of central corpuscles. All alcohol should be removed 

 from the tissues,* by means of distilled water before bringing 

 them into the mordant. This should be a 2-|- per cent, 

 solution of ferric alum, not iueaker. Leave the sections 

 therein (fixed to slides by the water method, § 186) for six 

 to twelve hours, or at least not less than three. Keep the 

 slides upright in the mordant, not lying fiat. Wash out trell 

 with water before staining. Stain in a " ripened " haeraa- 

 toxylin solution, i. e. one that has stood for four weeks [of 

 course, if you make it up with the ripened brown alcoholic 

 solution recommended § 237 siih. fin., this will be superfluous] . 

 Stain from twenty-four to thirty-six hours. U»e the name 

 staining solution over and over again until it becomes spoilt ; 

 for the solution after having been used gives a more ener- 

 getic stain, owing to its containing a trace of iron brought 

 over by the sections. Differentiate in a 2^ per cent, solu- 

 tion of ferric alum. Rinse for ten minutes in running water, 

 clear with xylol, not with any essential oil, and mount in 

 xylol -balsam. See also under '■' Centrosomes." 



BiEiASZEWics {Bull. Acad. Cracovie, 1909; 2 serie, p. 152) differen- 

 tiates with very weak solution of calciiim chloride ; Guaenieei (Mon. 

 Zool. Ital., xvii, 1906, p. 44) with saturated solution of picric acid. 



Gtjrwitsch {Zeit. iviss. Mik., xviii, 1902, p. 291) floods sections on 

 the slide with mordant, warms on a water-bath till bubbles are given off 



* Why ? I find my iron-ahim solution, as well as the liquor ferri 

 sw'ph. oxicl., last §, mix clear with alcohol without the least precipitate 

 forming. 



