oloured glass or a
stable coloured solution serves as a measure for the depth of colour of
the blood. There are a number of instruments of this kind, of which the
"haemometer" of Fleischl, and amongst others, the "haemoglobinometer" of
Gowers, distinguished by its low price, are specially used for clinical
purposes. Both instruments give the percentage of the haemoglobin of
normal blood which the blood examined contains, and are sufficiently
exact in their results for practical purposes and for relative values;
although errors up to 10% and over occur with unpractised observers.
(Cp. K. H. Mayer.) Quite recently Biernacki has raised the objection to
the colorimetric methods of the quantitative estimation of haemoglobin,
that the depth of colour of the blood is dependent not only on the
quantity of haemoglobin but also on the colour of the plasma, and the
greater or less amount of proteid in the blood. These errors are quite
inconsiderable for the above-mentioned instruments, since here the blood
is so highly diluted with water that the possible original differences
are thereby reduced to zero.

Among the methods for indirect haemoglobin estimation, that of
calculation from the amount of iron in the blood appears to be quite
exact, since haemoglobin possesses a constant quantity of iron of 0.42
per cent. This calculation may be allowed in all cases for normal blood,
for here there is a really exact proportion between the amounts of
haemoglobin and of iron. Recently A. Jolles has described an apparatus
for quantitative estimation of the iron of the blood, called a
"ferrometer;" which renders possible an accurate valuation of the iron
in small amounts of blood. However for pathological cases this method of
haemoglobin estimation from the iron present is not to be recommended.
For if one tests the blood of an anaemic patient under the microscope for
iron one finds the iron reaction in numerous red blood corpuscles. This
means the presence of iron which is not a normal constituent of
haemoglobin. Other iron may be contained in the morphological elements
(including the white corpuscles) as a combination of proteid with iron,
which is not directly recognisable. It is further known that in anaemias
the amount of iron of all organs is greatly raised (Quincke), apparently
often the result of a raised destruction of haemoglobin ("waste iron,"
"spodogenous iron"). In many cases too, it should be borne in mind that
the administratio