Form of cancer that originates in the white blood cells. There are various forms. The first distinction is made between acute and chronic leukaemia. A second subdivision depends on the type of white blood cell that has caused the condition. White blood cells can be divided into two kinds: those which play a part in aspecific immunity (granulocytes) and those which play a part in specific immunity (lymphocytes). The former give rise to myeloid leukaemia, and the latter to lymphatic leukaemia; each of these conditions can be acute or chronic. The first symptoms of acute leukaemia are fatigue, headache, fever and a sore throat; sometimes the lymph nodes are somewhat swollen. These symptoms are like those of a normal, not too serious infectious disease or glandular fever. It is therefore necessary to prepare a blood smear, in which the white blood cells can be counted and examined. If this does not provide a clear picture, a lumbar puncture can be made to ascertain the number of white blood cells present in the spinal fluid. Acute lymphatic leukaemia is most common in young children, and is the least serious form; 90 per cent of patients recover completely. Acute myeloid leukaemia is most common in adults, and is more serious in that it can lead to severe infection; the ‘sick’ white blood cells can no longer fulfil their defence function against bacteria and viruses, and serious haemorrhage is also possible as the blood platelets are driven out by the tumour cells. Chronic myeloid leukaemia occurs above all in older people, and is the