1. Severe infection—good resistance; early, marked and persistent leucocytosis.
2. Slight infection—slight resistance; leucocytosis present, but not marked.
3. In fulminating infections we may have no increase in whites, but a higher percentage of polymorphonuclears.
4. Slight infection and good resistance may not be productive of leucocytosis.
It is in connection with the question of operation in appendicitis or similar conditions that the matter of a leucocyte count is of prime importance. If there be a leucocytosis but with less than 75% of polymorphonuclears it indicates an infection of little virulence or a walled-off process with an exacerbation. It is difficult to form an opinion when the polymorphonuclears are under 80%. Leucocytosis with polymorphonuclear percentage of 85 to 90 indicates immediate operation; percentages over 90 point to peritonitis and if with such percentages of polymorphonuclears there is absence of leucocytosis the prognosis is grave.
The blood of cases with malignant tumors tends to show a moderate leucocytosis except in epithelioma of the skin. When a cancer is ulcerating quite a high white count may be obtained.
Spirochaete fevers, as relapsing fever, may give a leucocytosis of from 25,000 to 50,000.
Smallpox, especially at time of pustulation, plague, scarlet fever, and liver abscess give a leucocytosis of from 12,000 to 15,000.
Smallpox often shows a very large percentage of very characteristic large mononuclears.
The leucopenia and lymphocyte increase in measles are important points in differentiating it from scarlatina.