he analytic colour methods the fundamental
difference between the two conditions was first disclosed. Leucocytosis
is now recognised to be chiefly an increase of the normal polynuclear
neutrophil leucocytes; whereas myelogenic leukaemia brings elements into
the blood that are abnormal. The cells here introduced are so
characteristic as to render the diagnosis of leukaemia possible, even in
the very rare cases where the total number of the white blood corpuscles
is not to any extent increased. The best example of which we are aware
is a case observed by v. Noorden, in which the proportion of white to
red was only 1:200.

Although the blood picture of myelogenic leukaemia has been so clearly
drawn by Ehrlich, misconceptions and obscurities still occur in the
literature. And they are due to great errors in observation. It has for
instance happened that unskilled observers have regarded and worked up
cases of lymphatic leukaemia as myelogenic. The apparent deviations
discovered in this manner are copied, as specially remarkable, from one
book to another. Through insufficient mastery of the staining method,
the characteristic and diagnostically decisive elements (neutrophil
myelocytes for example) are frequently mistaken. A further source
productive of misconceptions lies in the circumstance that the typical
leukaemic condition of the blood may essentially change under the
influences of intercurrent diseases. Thus the intrusion of a
leucocytosis, brought about by secondary infection, is able to
obliterate more or less the specific character of the blood. Such
conditions must naturally be considered apart, and should not be used to
overthrow the general characteristics of the picture. No one surely
would deny the diagnostic value of glycosuria for diabetes, because in
conditions of inanition, for instance, the sugar of a diabetic may
completely vanish, although the disease continues. And one does not deny
the diagnostic value of the splenic tumour in typhoid fever, because the
enlargement of the spleen may occasionally subside, under the influence
of an intestinal haemorrhage.

From these considerations it is obviously necessary to derive the
description of leukaemic blood from pure uncomplicated cases; and to
construct it with the aid of standard methods. In this manner a type is
obtained so characteristic, as to render diagnosis absolutely certain
from the blood alone.

It is needful here to emphasise this hundred-fold r