nt. It consists in fixing the dry preparation
for 20 minutes in osmic acid vapour, and staining in a concentrated
watery solution of methylene blue.

* * * * *

With regard to the significance of the blood platelets, most authors, of
whom we should before all mention Hayem, Bizzozero, Laker, assume
justifiably that they are preformed in the living blood. The view
opposed to this, advocated more particularly by Loewit, that these forms
first arise in the blood after it has left the vessels, we may describe
on the grounds of our own extensive observations as inaccurate.

The blood platelets, on the grounds of their small size and complete
lack of nuclear substance, are generally regarded as not analogous to
real cells. Whether they represent intravital precipitation of
substances of the plasma, or whether they are budded off from the cells,
cannot at the present be decided with certainty, though many facts seem
to support the latter assumption. That they contain glycogen (see p.
45), marks them as descendants of the blood cells. Moreover, appearances
are often met with in dry preparations that arouse the suspicion that
the platelets arise from the red blood corpuscles (Koeppe). Arnold has
further observed processes of budding in the red blood corpuscles not
only extravascularly but also intravascularly in the mesentery of young
guinea-pigs, and has seen the elements that were cut off change into
forms free from haemoglobin.

Our knowledge too of the physiological function of the blood platelets
still needs much amplification. The original view of Hayem, who regards
the blood platelets as early stages of the red blood discs, and for this
reason calls them "haematoblasts," is, according to the judgment of most
haematologists, untenable.

Nearly all more recent papers, on the other hand (cp. Loewit's
compilation), recognise the =close connection of the blood platelets with
coagulation=, first observed by Bizzozero. Whether the substance of the
platelets directly yields the material for fibrin formation, as
Bizzozero holds, or whether according to the observations on thrombus
production of Eberth and Schimmelbusch they play but a subordinate part,
is not yet decided. To enter here into the chemical side of this
complicated problem, would lead us much too far, and we will only refer
to a few clinical observations which illustrate the relations between
the clotting power of the blood and the