ranging from 15,000 to 20,000. In children under one year of age, the
normal average is from 10,000 to 20,000.

_Absence of Leucocytosis--Leucopenia._--In certain infective diseases
the number of leucocytes in the circulating blood is abnormally
low--3000 or 4000--and this condition is known as _leucopenia_. It
occurs in typhoid fever, especially in the later stages of the disease,
in tuberculous lesions unaccompanied by suppuration, in malaria, and in
most cases of uncomplicated influenza. The occurrence of leucocytosis in
any of these conditions is to be looked upon as an indication that a
mixed infection has taken place, and that some suppurative process is
present.

The absence of leucocytosis in some cases of virulent septic poisoning
has already been referred to.

It will be evident that too much reliance must not be placed upon a
single observation, particularly in emergency cases. Whenever possible,
a series of observations should be made, the blood being examined about
four hours after meals, and about the same hour each day.

The clinical significance of the blood count in individual diseases will
be further referred to.

_The Iodine or Glycogen Reaction._--The leucocyte count may be
supplemented by staining films of the blood with a watery solution of
iodine and potassium iodide. In all advancing purulent conditions, in
septic poisonings, in pneumonia, and in cancerous growths associated
with ulceration, a certain number of the polynuclear leucocytes are
stained a brown or reddish-brown colour, due to the action of the iodine