THE MICROTOMIST'S VADE-MECUM

"The colouring material of logwood consists of two substances,
bomatoxylin and huematein, differing from one another by two   cota
equivalents of hydrogen. .Hematoxylin is soluble in alum
solution, whilst hematein is hardly at all so. The latter is
of no use to the histologist for colouring animal tissues.
Hmatoxylin forms compounds with various metallic oxides,       ai
which are soluble in alum   solution also, and if a tissue be   stt
stained with hu-matoxylin, or with huematoxylin and a metallic  But it
oxide and immersed in an aqueous solution of alum, the colour   sdtiO
will be all discharged from the tissue and taken up by the
solution, and the solution of alum will thus take up fresh
quantities of huematoxylin compound until it reaches a point
of saturation beyond which it will take up no more from the
tissues, but will, if over-saturated, give up the colouring matter
freely to immersed animal material.     Such a solution of
bematoxylin, alum, and metallic oxide has a clear purple
colour, becoming red on addition of acids. If alkaline earths,
alumina, or hydrated earthy phosphates be suspended in it,
they will absorb the colour and the solution becomes purple' thicl1
If the solution be treated with a very small percentage of a,
chromate, the purple will be replaced by a yellowish-brown
colour; or if a tissue which has been stained with alum log-
wood solution be immersed in an exceedingly dilute bichro-
mate solution, the purple will sooner or later be replaced by     a
the yellow tint. If a section of any abnormal caseous con-
cretion or abnormal growth be immersed in a neutral solution
of alum logwood, it will become of a more bluish purple
than ordinary tissue, evidently from  the presence in it of       ue
more than an ordinary amount of alkaline earthy matter or
phosphate.                                                        any
" When the above facts are taken into consideration it will     sODe
appear unreasonable to expect tissues hardened in chromic
solutions of any kind to colour as readily with an ordinary
logwood solution as they would do if immersed in the fresh         kEy
state, notwithstanding the assertion of any experimenters to the    t

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