The FIRST or PRELIMINARY STAGE lasts a variable time, according to the suddenness and completeness with which the access of air is prevented; it lasts until there is a demand for the air. In a case of homicide, injuries may be inflicted on the victim in this stage which may have an important bearing on the cause of death. Blows on the head may cause unconsciousness, or even apoplexy; upon the stomach, may cause syncope; stab-wounds may tend to cause death from hemorrhage.
The SECOND STAGE begins with the demand for air and lasts till unconsciousness supervenes. It is characterized by frantic efforts to breathe, efforts in which the entire body takes part. If the subject is conscious, he is intensely so; the expression of the face is intense; the eyes may protrude, the hands be clinched; the memory is unusually active, and the events of a lifetime may rapidly pass before the mind in a few minutes. The tongue may be thrust between the clinched teeth and bitten; and urine, fæces, and semen may be discharged.
The THIRD STAGE usually appears suddenly, and is characterized by unconsciousness and irregular involuntary movements, i.e., spasms; these may end in opisthotonos; the veins become turgid, and hemorrhages may occur from the eyes, nose, mouth, throat, ears, and into the connective tissues of the lungs, pleura, pericardium, etc. The circulation of venous blood in the arteries is shown by the general lividity, especially where the skin is thin, as the lips and tips of fingers. Hofmann[736] states that coincident with the oncoming of unconsciousness and convulsions the respiratory effort becomes expiratory, followed still later by inspiratory efforts.
The FOURTH STAGE begins with the cessation of spasms and of efforts to breathe. The subject is quiet, but the heart still beats. The stage ends with the cessation of the heart-beat.
Discharges of semen, urine, and fæces may occur in the first and second stages, from terror; in the second and third from the general agitation, and in the third and fourth from paralysis.
Strangulation according to Bernard[737] causes a rise in temperature, varying from one to two degrees (Cent.). He thinks that this is due to the changes from arterial to venous blood, especially in the muscles.
Lukomsky[738] concluded from experiments that in asphyxia both arterial and venous pressure is increased in the systemic circulation, but diminished in the pulmonary artery. The highest degree of blood pressure coincides with the strongest respiratory movements, especially expiration. He also concluded that the Tardieu spots (subpleural ecchymoses) directly depended on the efforts of breathing and blood pressure.
Some writers, as Taylor and Tidy, think that death occurs sooner in the human subject than in the lower animals; where the access of air is suddenly and completely prevented death may be immediate. Tardieu says that death follows pressure of the hand sooner than that of a ligature.
Fleischmann[739] placed cords round his own neck between hyoid bone and chin, tied them tightly, sometimes at the side, sometimes at the back, without respiration being interfered with, because there was no pressure on the air passages. But his face grew red, eyes protruded slightly, there was a feeling of great heat in the head, of weight, commencing dizziness, and suddenly a hissing and rustling in his ears. The experiment should stop at this point. The same symptoms occurred from applying the cord over the larynx. The first experiment lasted two minutes, the second a half-minute. The difference was due to the different situation of the cord.