Hæmatoxyline stains the nuclei of the cells a beautiful violet colour, and also tints, more or less lightly, the cell protoplasm and the fibrous elements. It also stains the axis cylinders of nerves, and is much used in special staining of the nerve centres as will be described later, (pp. [88]–91).
The stain is permanent. Sections may be mounted either in Farrant’s solution, or in Canada balsam, the latter being preferable.
Eosine.—Much more satisfactory results are obtained from the commercial eosine (an amorphous orange powder used in dyeing and in the manufacture of red ink), than from the pure crystalline form.
It may be used as an aqueous solution ( 1/30 per cent.) or as a solution in absolute alcohol ( 1/15 per cent.). Sections stained in the former should be rapidly passed through a one per cent. solution of acetic acid in order to “fix” the stain, and then washed in distilled water.
It is a very transparent stain, and the most delicate details of a section stained with it are perfectly visible.
It stains the nucleus but slightly, while it stains the cell protoplasm and fibrous tissues and especially muscular tissues a beautiful rose colour.
It will be seen, therefore, that it stains those parts which are left unstained by hæmatoxyline, and vice versâ. This complementary action is applied in the following method.
Double staining with eosine and hæmatoxyline.—Sections having been stained in hæmatoxyline in the ordinary way, are washed in distilled water, and dehydrated in a solution (about 1 in 1500) of eosine in absolute alcohol. They should remain in this for about two minutes, and then be passed through oil of cloves and mounted in Canada balsam in the ordinary way.
This method gives extremely useful and beautiful results with almost all tissues, and is superior to picrocarmine for differentiating the tissue elements. Thus, the nuclei are stained violet, the cell protoplasm a much paler and warmer violet, the fibrous tissues pink, and red blood corpuscles orange or brick red.
The alcoholic solution of eosine is also used as a contrast stain after staining for micro-organisms with blue or violet dyes.