observer the depth of stain gives a certain indication of the haemoglobin
equivalent of each cell, and a better one than the natural colour of the
haemoglobin in the fresh specimen. Corpuscles poor in haemoglobin are
easily recognised by their fainter staining, especially by the still
greater brightness of the central zone. When somewhat more marked, they
present appearances which from the isolated staining of the periphery
Litten has happily named "pessary" forms. The faint staining of a red
corpuscle cannot be explained, as E. Grawitz assumes, by a diminished
affinity of the haemoglobin for the dye. Qualitative changes of this kind
of the haemoglobin, expressing themselves in an altered relationship
towards dyes, do not occur, even in anaemic blood. If in the latter, the
blood discs stain less intensely, this is due exclusively to the smaller
amount of haemoglobin.

A diminution in the haemoglobin content can in this way be shewn in all
anaemic conditions, especially in posthaemorrhagic, secondary and
chlorotic cases. On the contrary, as Laache first observed, in the
pernicious anaemias, the haemoglobin equivalent of the individual discs is
raised.

To appreciate correctly pathological conditions, it must always be borne
in mind, that in normal blood the individual red blood corpuscles are by
no means of the same value. Step by step some of the cells are used up
and replaced by new. Every drop of blood contains, side by side, the
most various stages of life of fully formed erythrocytes. For this
reason influences which affect the blood--provided their intensity does
not exceed a certain degree--cannot equally influence all red
corpuscles. The least resistant elements, that is, the oldest, will
succumb to the effect of influences, to which other and more vigorous
cells adapt themselves.

To influences, of this moderate degree, belongs without doubt the anaemic
constitution of the blood as such, the effect of which in this direction
one can best investigate in cases of posthaemorrhagic anaemia.

In all anaemic conditions we observe characteristic changes in the blood
discs.

A. =Anaemic or polychromatophil degeneration.=

This change in the red blood corpuscles, first described by Ehrlich, to
which the second name was given later by Gabritschewski, is =only
recognisable in stained preparations=. The red blood discs, which under
normal circumstances stain in pure haemoglobin colour, now take on a
mixed colour.