Leucocythemia (Gr. leukos, 'white,' cytos, 'a cell,' and hæma, 'blood') is a disease in which the number of white corpuscles in the blood is greatly increased, while there is a simultaneous diminution of the red corpuscles. The disease was noticed almost at the same time (in 1845) by John Hughes Bennett of Edinburgh and Virchow of Würzburg; the former giving in 1852 the name Leucocythemia, while the latter gave it in 1847 the less expressive name of Leukæmia or White Blood. The increase of the white or colourless corpuscles seems to be always accompanied, and probably caused, by changes in some of the lymphatic tissues of the body. Of these by far the most common is enlargement of the spleen, which sometimes attains an enormous size. In many cases this is associated with enlargement of lymphatic glands, and less commonly with a peculiar change in the marrow of the bones; and occasionally one or both of these conditions may be present without enlargement of the spleen.
The first symptom usually noticed by the patient is enlargement of the abdomen, in consequence of the increase in size of the spleen. Weakness, breathlessness, haemorrhages in various situations, and often enlargement of the liver succeed; and the disease almost always proves fatal in two or three years at most. It may occur at any age; but is most common between twenty and fifty, and in the male sex. Nothing is known as to its cause, except that a considerable proportion (one-fifth or more) of those affected have at some previous time suffered from ague. Treatment seems sometimes to have proved effectual in the early stages; cases have been recorded where quinine, phosphorus, cod-liver oil, iodide of iron have arrested what appeared to be commencing leucocythemia. But after the disease is fully established all treatment has as yet proved unavailing.