ISTANCE OF
THE RED BLOOD CORPUSCLES to external injuries of various kinds.

Landois, Hamburger and v. Limbeck ascertain for instance the degree of
concentration of a salt solution, in which the red corpuscles are
preserved ("isotonic concentration," Hamburger) and those which cause an
exit of the haemoglobin from the stroma. The erythrocytes are the more
resistant, the weaker the concentration which leaves them still
uninjured.

Laker tests the red blood corpuscles as regards their resistance to the
electric discharge from a Leyden jar, and measures it by the number of
discharges up to which the blood in question remains uninjured.

Clinical observation has not yet gained much by these methods. So much
only is certain, that in certain diseases: anaemia, haemoglobinuria, and
after many intoxications, the resistance, as measured by the methods
above indicated, is considerably lowered.

FOOTNOTES:

[1] For the estimation of the numbers of white corpuscles, relatively to
the red, and of the different kinds relatively to each other, see the
section on the morphology.

[2] In Roy's method, mixtures of glycerine and water are used. By means
of a curved pipette, the drop of blood is brought into the fluid, and
its immediate motion observed. Lazarus Barlow has modified this method.
He employs mixtures of gum and water, and instead of several tubes, one
only; and into this the mixtures are introduced, those of higher
specific gravity being naturally at the bottom. The alternate layers are
coloured, and remain distinguishable for several hours.

[3] In conditions of shock experimentally produced, the specific gravity
of the total blood is increased, that of the plasma, however, is
diminished (Roy and Cobbett).

THE MORPHOLOGY OF THE BLOOD.

A. METHODS OF INVESTIGATION.

A glance at the history of the microscopy of the blood shews that it
falls into two periods. In the first, which is especially distinguished
by the work of Virchow and Max Schultze, a quantity of positive
knowledge was quickly won, and the different forms of anaemia were
recognised. But close upon this followed a standstill, which lasted for
some decades, the cause of which lay in the circumstance that observers
confined themselves to the examination of fresh blood. What in fact was
to be seen with the aid of this simple method, these distinguished
observers had quickly exhausted. That these methods were inadequate is
best shewn by the hi