PURPURIN. 131 



(As regards the quantity of alcohol to be taken, Duval 

 writes that it should always be one fourth in volume of the 

 total mixture Precis de Technique histologique, p. 221.) 



The solution does not keep well for more than a few weeks. 



Sections of fresh cartilage are to be placed in a small 

 quantity (only a few cubic centimetres) of the solution, and 

 after remaining there twenty-four to forty-eight hours are 

 washed in water and mounted in glycerin. The stain is 

 nuclear, the matrix remaining almost colourless. Duval (loc. 

 cit.) states that this stain has a special selective action on 

 sections of central nervous system (especially spinal cord) 

 obtained from tissues hardened in bichromate of ammonia 

 (2 1000), and mounted, after staining for forty-eight hours, 

 in Canada balsam. The nerve cells and processes, axis-cylin- 

 ders, and fibres of connective tissue are unstained; but the 

 nuclei of connective tissue and of the capillaries are stained 

 red. 



GTRENACHEK'S formula (Arch. f. mik. Anat., xvi, 1879, p. 470). 

 In 50 cubic centimetres of glycerin (pure or diluted with 

 very little water) dissolve from 1 to 3 per cent, powdered 

 alum; add a knife-pointful of purpurin, and boil. (Alcohol 

 must not be added.) Let the orange-coloured fluorescent 

 solution stand for two or three days, and then filter. 



A nuclear stain ; ten to thirty minutes generally suffice to 

 produce good staining. The solution is stable, which Grenacher 

 finds that Ranvier's solution is not, the latter precipitating 

 after a few days. 



202. Indigo. Indigo is employed in histology in the form of solutions 

 of so-called indigo-carmine, or sulphindigotate of soda or potash. The 

 simple aqueous solution gives a diffuse stain, and is therefore not capable of 

 being usefully employed alone. It is, however, of great use when employed 

 to bring about a double stain in conjunction with carmine. Though it has 

 no selective preference for nuclei or protoplasm, it possesses to a high 

 degree the property of imparting different hues and intensity of stain to 

 different tissues ; and the nuclei being brought out by carmine, prepara- 

 tions are obtained of a diagrammatic clearness that is not afforded by car- 

 mine alone. 



Indigo-carmine is found in commerce. The reader who may desire to 

 prepare it himself will find the necessary directions in Arch. /. mik. Anat. y 

 x, 1874, p. 32, and in Journ. Roy. Micr. Soc., ii, 1879, p. 614 



203. Thiersch's Oxalic Acid Indigo-carmine (see Arch. f. mik. 

 Anat., i, 1865, p. 150). 



204. Tincture of Saffron (H. BLANC, Zool. Anzeig., 129, 1883, p. 23). 



