s, however, used in medicine to imply something more
than its Greek origin denotes, namely, a complete and prolonged loss of
consciousness from which a patient cannot be roused. There are various
degrees of coma: 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, and such are met
with in apoplexy, already described. Coma may arise abruptly in a
patient who has presented no pre-existent indication of such a state
occurring. Such a condition is called _primary coma_, and may result
from the following causes:--(1) concussion, compression or laceration of
the brain from head injuries, especially fracture of the skull; (2) from
alcoholic and narcotic poisoning; (3) from cerebral haemorrhage,
embolism and thrombosis, such being the causes of apoplexy. _Secondary
coma_ may arise as a complication in the following diseases:--diabetes,
uraemia, general paralysis, meningitis, cerebral tumour and acute yellow
atrophy of the liver; in such diseases it is anticipated, for it is a
frequent cause of the fatal termination. The depth of insensibility to
stimulus is a measure of the gravity of the symptom; thus the
conjunctival reflex and even the spinal reflexes may be abolished, the
only sign of life being the respiration and heart-beat, the muscles of
the limbs being sometimes perfectly flaccid. A characteristic change in
the respiration, known as Cheyne-Stokes breathing occurs prior to death
in some cases; it indicates that the respiratory centre in the medulla
is becoming exhausted, and is stimulated to action only when the
venosity of the blood has increased sufficiently to excite it. The
breathing consequently loses its natural rhythm, and each successive
breath becomes deeper until a maximum is reached; it then diminishes in
depth by successive steps until it dies away completely. The condition
of apnoea, or cessation of breathing, follows, and as soon as the
venosity of the blood again affords sufficient stimulus, the signs of
air-hunger commence; this altered rhythm continues until the respiratory
centre becomes exhausted and death ensues.

_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; he is entirely
insensible to his surroundings, and neither knows nor can