these phenomena
by a deficient activity of the bone-marrow, which found expression in
the insufficient formation of red and white blood corpuscles. As the
anatomical basis of this deficient activity, he conjectured that in this
case the fatty marrow of the big long bones could not have been changed
to blood forming red marrow, as is the rule in severe anaemias. In two
cases the autopsy fully confirmed this diagnosis made during life.

The blood platelets.--The haemoconiae.

The ~blood-platelets~ were first described by Hayem, later by Bizzozero,
as a third formed element of normal blood. They are roundish or oval
discs free from haemoglobin. They are extremely unstable under
mechanical, thermal, and chemical influences. Their size amounts to some
3 mu. Specially characteristic is their tendency, the result of their
extraordinary stickiness, to run together into largish clumps, "grape
clusters." This circumstance greatly facilitates the distinction of the
blood platelets from the other formed elements, but renders their
enumeration most difficult. The apparatus usually used for counting the
blood corpuscles is, for this reason, deceptive; for the platelets
rapidly cling to its walls and remain there. All early authors (_e.g._
Bizzozero) endeavoured to obviate this error by some particular diluting
fluid; but a number of these elements still remained fastened to the
walls of the capillary tube of the mixing apparatus.

Recently Brodie and Russell have recommended a new mixture in which the
platelets remain quite isolated, and are stained at the same time. They
allow the drop of blood as it comes from the puncture to enter a drop of
the fluid, and then estimate the relative proportion of red blood
corpuscles to platelets[36]. The prescription for their solution is as
follows:

Dahlia-glycerin,
2% solution of common salt ... equal parts.

Another method, used by the majority of more recent authors, is the
relative enumeration of blood platelets in the stain dry specimen.
Ehrlich found that the blood platelets were picked out by their deep red
colour, corresponding to the amount of alkali they contain, in
preparations treated by the iodine eosine method (see p. 46). Rabl's new
method is much more complicated and in no way more serviceable,
depending on a stain with iron haematoxylin recommended by E. Haidenhain
for demonstration of the centrosomes. A process of Rosin's, not yet
published, is more convenie