102 COCHINEAL AND OTHER ORGANIC STAINS. 



stained. (Ranvier found that alum in a solution of 5 1000 was 

 the best of all fixing agents for cartilage-cells, Traite, p. 279.) 



RANViER's/ormwZo. (Traite Technique, p. 280). 200 grammes 

 of water and 1 of alum are boiled in a porcelain capsule ; pur- 

 purin rubbed up in water is added, and the boiling continued. 

 The purpurin being dissolved to saturation (this is ensured by 

 taking care to have an undissolved excess in the capsule), the 

 solution is filtered hot into a flask containing 60 c.c. of alcohol 

 (36 Cartier, = 90 per cent). 



There is thus obtained a solution of an orange-rose colour, 

 presenting a marked degree of fluorescence. 



(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 (1. c.) 

 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 cylinders, and 

 fibres of connective tissue, are unstained ; but the nuclei of 

 connective tissue and of the capillaries are stained red. 



GRENACHER'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 ; added 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 Grenadier 

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

 after a few days. 



190. 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 



