any have anything more than a general idea as to the significance of a
hypoleucocytosis or a hyperleucocytosis in a case of acute pneumonia, or
as to the relations of cells of different forms and the percentage
quantity of haemoglobin found in the various types of anaemia?

One of the most important points indicated in the following pages is
that the cellular elements of the blood must be studied as a whole and
not as isolated factors, as "it has always been shown that the character
of a leukaemic condition is only settled by a concurrence of a large
number of single symptoms of which each one is indispensable for the
diagnosis, and which taken together are absolutely conclusive."
Conditions of experiment can of course be carefully determined, so far,
at any rate, as the introduction of substances from outside is
concerned, but we must always bear in mind that it is impossible, except
in very special cases of disease, to separate the action of the
bone-marrow from the action of the lymphatic glands; still, by careful
observation and in special cases, especially when the various organs and
parts may be examined after death, information may be gained even on
this point. By means of experiment the production of leucocytosis by
peptones, the action of micro-organisms on the bone-marrow, the
influence of the products of decaying or degenerating epithelial or
endothelioid cells, may all be studied in a more or less perfect form;
but, withal, it is only by a study of the numerous conditions under
which alterations in the cellular elements take place in the blood that
any accurate information can be obtained.

Hence for further knowledge of the "structure" and certain functions of
the blood we must to a great extent rely upon clinical observation.

Some of the simpler problems have already been flooded with light by
those who following in Ehrlich's footsteps have studied the blood in
disease. But many of even greater importance might be cited from the
work before us. With the abundant information, the well argued
deductions and the carefully drawn up statement here placed before us it
may be claimed that we are now in a position to make diagnoses that not
long ago were quite beyond our reach, whilst a thorough training of our
younger medical men in the methods of blood examination must result in
the accumulation of new facts of prime importance both to the
pathologist and to the physician.

Both teacher and investigator cann