story of leucocytosis, which after the precedent of
Virchow was in general referred to an increased production on the part
of the lymphatic glands; and further by the imperfect distinction
between leucocytosis and incipient leukaemia, which was drawn almost
exclusively from purely numerical estimations. It was only after Ehrlich
had introduced the new methods of investigation by means of stained dry
preparations, that the histology of the blood received the impulse for
its second period.

We owe to them the exact distinction between the several kinds of white
blood corpuscles, a rational definition of leukaemia, polynuclear
leucocytosis, and the knowledge of the appearances of degeneration and
regeneration of the red blood corpuscles, and of their degeneration in
haemoglobinaemic conditions. The same process, then, has gone on in the
microscopy of the blood that we see in other branches of normal and
pathological histology: by advances in method, advances in knowledge
full of importance result. It is therefore little comprehensible, that
an author quite recently should recommend a reversion to the old
methods, and emphatically announce that he has managed to make a
diagnosis in all cases, with the examination of fresh blood. At the
present time, after the most important points have been cleared up by
new methods, in the large majority of cases, this is not an astonishing
achievement. For any difficult case (for instance the early recognition
of malignant lymphoma, certain rare forms of anaemia, etc.) as the
experienced know, the dry stained preparation is indispensable. The
object of examining the blood, is certainly not to make a rapid
diagnosis, but to investigate exactly the individual details of the
blood picture. To-day, we can only take the standpoint, that everything
that is to be seen in fresh specimens--apart from the quite unimportant
rouleaux formation, and the amoeboid movements--can be seen equally
well, and indeed much better in a stained preparation; and that there
are several important details which are only made visible in the latter,
and never in wet preparations.

As regards the purely technical side of the question, the examination of
stained dry specimens is far more convenient than that of fresh. For it
leaves us quite independent of time and place, we can keep the dried
blood with few precautions for months at a time, before proceeding to
further microscopic treatment; and the examination of the