PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 207 



should be used in a strong watery solution; and the sections must be well washed 

 in water after staining. Its chief use is in ' double staining ' ( 203). 



/. For blue and green staining, the various Aniline dyes are principally used. 

 They are, for the most part, however, rather fugitive in their effects; not forming 

 durable combinations with the tissues they stain. Some of them are soluble in 

 water, others only in spirit; and the selection between the dyes of these two classes 

 will have to be guided by the mode in which the preparations are treated. These 

 dyes are for the most part best fixed by benzole; and as the sections treated with 

 this fluid may be at once mounted in Canada balsam, there is greater probability 

 of their colors being preserved. Besides blue and green, the Aniline series fur- 

 nishes a deep rich brown, known as Bismarck's Brown; and a blue-black, which 

 has been recommended for staining nerve-cells. 



g. A good blue stain (tending to purple) is also given by the substance termed 

 Indigo-Carmine; which is particularly recommended for sections of the brain and 

 spinal cord that have been hardened* in chromic acid. A saturated solution of 

 the powder in distilled water having been prepared, this may either be used with 

 the addition of about 4 per cent of oxalic acid; or, if an alcoholic fluid be pre- 

 ferred, methylated spirit may be added to the aqueous solution, the mixture being 

 filtered to remove any coloring matter that may have been precipitated. If sec- 

 tions thus stained have an excess of color, this may be removed by the action of 

 a saturated solution of oxalic acid in alcohol. 



h. A beautiful green hue is given by treating with a saturated solution of 

 Picric acid in water, sections previously stained with Aniline blue; or the two 

 agents may be used together, 4 or 5 parts of a saturated solution of the latter be- 

 ing added to a saturated aqueous solution of the former. This picro-aniline, it is 

 believed, may be relied on for permanence; and it acts well in double staining 

 with picro-carmine. 



i. Two chemical agents, Nitrate of Silver and Chloride of Gold, are much used 

 by Histologists for bringing-out particular tissues; the former being especially 

 valuable for the staining of Epithelium-cells; the latter for staining Nerve-cells, 

 Connective-tissue corpuscles, Tendon-cells, and Cartilage-cells. The most advan- 

 tageous use of these can only be made by the careful observance of the directions 

 'which will be found in treatises on Practical Histology. 



k. Molybdate of Ammonia is recommended as affording a cool blue-gray or 

 neutral-tint general stain, which affords a pleasant 'ground' to parts strongly 

 colored by bright selective stains. 



203. Double and Triple Staining. Very instructive as well as beauti- 

 ful effects are produced by the simultaneous or successive action of two 

 or three staining fluids; which will respectively pick out (so to speak) the 

 parts of a section for which they have special affinities. Thus, if a section 

 through the base of the tongue of a cat or dog, be stained with picro- 

 carmine, rosein, and iodine-green, the muscles-fibres will take the first, 

 the connective tissue and protoplasm of cells will be colored by the second, 

 while the third will lay hold of the nuclei in the superficial epithelium, 

 serous glands, and non-striated muscle in the vessels; and, further the 

 mucous glands will show a purple formed by the combined action of the 

 red and green (Gibbes). ' A very, striking contrast of the like kind is 

 shown in the double staining of the frond of a Fern with log-wood and 

 aniline blue; the sori taking the latter, and standing out brilliantly on 

 the general surface tinged by the former. The effects produced by using 

 one stain after the other, are generally much better than those obtained 

 by simultaneous staining. The selective action of a second stain is not 

 prevented by a previous general staining; for the dye which gives the lat- 

 ter seems to be more weakly held by the parts which take the former, so 

 as to be (as it were) displaced by it. Thus, if a section of a Stem be 

 stained throughout by a solution of Eosin (2 grains to 1 oz.), and be then 

 placed, after washing in strong alcohol, in a half -grain solution of Nichol- 



1 See his " Practical Histology," Chap, v., and his Paper in " Journ. of Roy. 

 Microsc. Soc.," Vol. iii. (1880), p. 390. 



