Polymorphonuclear leukocytosis may be either physiologic or pathologic. A count of 20,000 would be considered a marked leukocytosis; of 30,000, high; above 50,000, extremely high. (1) Physiologic Polymorphonuclear Leukocytosis.--This is never very marked, the count rarely exceeding 15,000 per cubic millimeter. It occurs in the new-born, in pregnancy, during digestion, and after cold baths. There is moderate leukocytosis in the moribund state; this is commonly classed as physiologic, but is probably due mainly to terminal infection. {160} (2) Pathologic Polymorphonuclear Leukocytosis.--The classification here given follows Cabot: (_a_) _Infectious and Inflammatory_.--The majority of infectious diseases produce leukocytosis. The most notable exceptions are influenza, malaria, measles, tuberculosis, except when invading the serous cavities or when complicated by mixed infection, and typhoid fever, in which leukocytosis indicates an inflammatory complication. All inflammatory and suppurative diseases cause leukocytosis, except when slight or well walled off. Appendicitis has been studied with especial care in this connection, and the conclusions now generally accepted probably hold good for most acute intra-abdominal inflammations. A marked leukocytosis (20,000 or more) nearly always indicates abscess, peritonitis, or gangrene, even though the clinical signs be slight. Absence of or mild leukocytosis indicates a mild process, or else an overwhelmingly severe one; and operation may safely be postponed unless the abdominal signs are very marked. On the other hand, no matter how low the count, an increasing leukocytosis--counts being made hourly--indicates a spreading process and demands operation, regardless of other symptoms. Leukocyte counts alone are often disappointing, but are of much more value when considered in connection with a differential count of polymorphonuclears (see p. 181). (_b_) _Malignant Disease_.--Leukocytosis occurs in about one-half of the cases of malignant disease. In many instances it is probably independent of any secondary infection, since it occurs in both ulcerative and non-ulcerative cases. It seems to be more common in sarcoma than in carcinoma. Very large counts are rarely noted. {161} (_c_) _Post-hemorrhagic_.--Moderate leukocytosis follows hemorrhage and disappears in a few days. (_d_) _Toxic_.--This is a rather obscure class, which includes gout, chronic nephritis, acute yellow atrophy of the liver, ptomain poisoning, prolonged chloroform narcosis, and quinin poisoning. Leukocytosis may or may not occur in these conditions, and is not important. (_e_) _Drugs_.--This also is an unimportant class. Most tonics and stomachics and many other drugs produce a slight leukocytosis.