COMA, in medicine, a complete and prolonged loss of con sciousness from which a patient cannot be roused. There are various degrees : in the slighter forms the patient can be partially roused only to relapse again into a state of insensibility; in the deeper states, the patient cannot be roused at all. Coma may arise abruptly from (1) concussion, compression or laceration of the brain from head injuries, especially fracture of the skull; (2) alcoholic and narcotic poisoning; (3) cerebral haemorrhage, em bolism and thrombosis. It may also supervene in diabetes, uraemia, general paralysis, meningitis, sleeping and sleepy sickness, cerebral tumour and acute yellow atrophy of the liver. The depth of insensibility to stimulus is a measure of the gravity of the symptom ; thus the conjunctival reflex and even the spinal re flexes may be abolished, the only sign of life being the respiration and heart-beat. A characteristic change in respiration known as Cheyne-Stokes breathing occurs prior to death in some cases.
Coma Vigil is a state of unconsciousness met with in the algide stage of cholera and some other exhausting diseases. The patient's eyes remain open, and he may be in a state of low muttering delirium.
The word "coma" which is used in astronomy for the envelope of a comet and in botany for a tuft, though spelt the same in English, is derived from a different Greek word.