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There are three modes in which death may occur: (1) Syncope; (2) asphyxia; (3) coma.

1. Syncope is death beginning at the heart—in other words, failure of circulation. It may arise from—(1) Anæmia, or deficiency of blood due to hæmorrhage, such as occurs in injuries, or from bleeding from the lungs, stomach, uterus, or other internal organs. (2) Asthenia, or failure of the heart's action, met with in starvation, in exhausting diseases, such as phthisis, cancer, pernicious anæmia, and Bright's disease, and in some cases of poisoning—for example, aconite.

The symptoms of syncope are faintness, giddiness, pallor, slow, weak, and irregular pulse, sighing respiration, insensibility, dilated pupils, and convulsions.

Post mortem the heart is found empty and contracted. When, however, there is sudden stoppage of the heart, the right and left cavities contain blood in the normal quantities, and blood is found in the venæ cavæ and in the arterial trunks. There is no engorgement of either lungs or brain.

2. Asphyxia, or death beginning at the lungs, may be due to obstruction of the air-passages from foreign bodies in the larynx, drowning, suffocation, strangling, and hanging; from injury to the cervical cord; effusion into the pleuræ, with consequent pressure on the lungs; embolism of the pulmonary artery; and from spasmodic contraction of the thoracic and abdominal muscles in strychnine-poisoning.

The symptoms of this condition are fighting for breath, giddiness, relaxation of the sphincters, and convulsions.

Post mortem, cadaveric lividity is well marked, especially in nose, lips, ears, etc.; the right cavities of the heart and the venæ cavæ are found gorged with dark fluid blood. The pulmonary veins, the left cavities of the heart, and the aorta, are either empty or contain but little blood. The lungs are dark and engorged with blood, and the lining of the air-tubes is bright red in colour. Much bloody froth escapes on cutting into the lungs. Numerous small hæmorrhages (Tardieu's spots) are found on the surface and in the substance of the internal organs, as well as in the skin of the neck and face.

3. Coma, or death beginning at the brain, may arise from concussion; compression; cerebral pressure from hæmorrhage and other forms of apoplexy; blocking of a cerebral artery from embolism; dietetic and uræmic conditions; and from opium and other narcotic poisons.

The symptoms of this condition are stupor, loss of consciousness, and stertorous breathing.

The post-mortem signs are congestion of the substance of the brain and its membranes, with accumulation of the blood in the cavities of the heart, more on the right side than on the left.

It must be remembered that, owing to the interdependence of all the vital functions, there is no line of demarcation between the various modes of death. In all cases of sudden death think of angina pectoris and the rupture of an aneurism.

The following is a list of some of the commoner causes of sudden death:

(a) Instantaneously Sudden Death—

1 Syncope (by far the commonest cause).

2 Aortic incompetence.

3 Rupture of heart.

4 Rupture of a valve.

5 Rupture of aortic aneurism.

6 Embolism of coronary artery.

7 Angina pectoris.

(b) Less Sudden but Unexpected Death—

1 Cerebral hæmorrhage or embolism.

2 Mitral and tricuspid valvular lesions if the patient exerts himself.

3 Rupture of a gastric or duodenal ulcer; rupture of liver, spleen, or extra-uterine gestation, or abdominal aneurism.

4 Suffocation during an epileptic fit; vomited matter or other material drawn into the trachea or air-passages; croup.

5 Arterio-sclerosis may lead to thrombosis, embolism, or aneurism.

6 Poisoning, as by hydrocyanic acid, cyanide of potassium, inhalation of carbonic acid or coal gas, œdema of glottis following inhalation of ammonia.

7 Rapid onset of some acute specific disease, such as pneumonia or diphtheria; collapse from cholera.

8 Heat-stroke, lightning, shocks of electricity of high tension.

9 Mental or physical shock.

10 Exertion while the stomach is overloaded.

11 Diabetic coma; uræmia.

12 Status lymphaticus. This is a general hyperplastic condition of the lymphatic structures in the body, and is seen in enlargement of tonsils, thymus, spleen, as well as of Peyer's patches and mesenteric glands. It is a frequent cause of death during chloroform anæsthesia for slight operations in young people.

In addition, it may be as well to remember that death sometimes occurs suddenly in exophthalmic goitre, hypertrophy of the thymus, and in Addison's disease.

In some cases of sudden death nothing has been found post mortem, even when the autopsy has been made by skilled observers, and the brain and cord have been submitted to microscopical examination.