Quinquaud[730] and Fredericq[731] conclude from experiments on animals that asphyxia is due to the deficiency of oxygen, not to the accumulation of carbon dioxide.
Page[732] divides the phenomena witnessed in an animal killed by simply depriving it of air, without interfering with the blood-vessels of the neck, into four stages:
First. A short stage. (In the human subject this stage could scarcely last longer than fifty seconds, which is said to be the extreme limit of the most expert divers. The breath can be held longest if a number of deep breaths have previously been taken, so as to surcharge the blood with oxygen.)
Second. The stage of “besoin de réspirer,” when the want of air begins to be felt; the animal makes vigorous and violent efforts to overcome the obstacle. This stage may continue for three to four minutes.
Third. Unconsciousness supervenes with irregular and spasmodic movements; efforts at respiration continue.
Fourth. Efforts at respiration cease, but the heart still beats. This stage may last from two to four minutes. Hofmann[733] says that it may last a half-hour. In new-born infants, asphyxiated, it may be quite long.
The post-mortem appearances in such an animal were as follows: the lungs were pale, reddish, not much distended; there were a few dilated air-cells toward the anterior border; hemorrhages irregularly dispersed over the surface of the lung, varying in number and size. The right cavities of the heart contained dark fluid blood, the left were empty. The pulmonary artery and systemic veins, even the smallest branches, were gorged with dark blood. Page adds that when the great vessels of the neck are interfered with death may occur “by coma, syncope, and even asthenia.”
Colin[734] made twenty-five experiments on horses, and records three of them as follows: they were all strangled with a hempen cord at the middle of the neck. The first was quiet till the second or third minute, then there were violent movements and strong efforts to dilate the chest; at four minutes, spasms; four and one-half minutes, quiet; six minutes, pupils dilated, tongue hanging out, limbs flaccid; blood black. Second horse: Carotid artery denuded to observe its action. In fifteen seconds, blood nearly black; four and one-quarter minutes, no pulsation in carotids; five and one-half minutes, no respiratory movement; six minutes, heart-beat ceased, except feeble contraction of auricles, which continued till twenty-first minute. Third horse: In five minutes respiration ceased; tracheotomy performed, but there was no attempt to breathe; eight minutes, heart ceased to beat. Similar results were obtained in ruminants and in small animals, except that the larger animals lived longer than the smaller.
Faure[735] made the following experiment on a large dog. He tied a cord tightly round its neck; for fifty-five seconds it was quiet, then suddenly it became agitated, threw itself against the wall, rolled on the ground, twisted itself; bloody mucus escaped from the nose and mouth; the teeth were ground together; urine and fæces were passed. The efforts at respiration became very rapid. It fell dead at the end of three and one-half minutes.
The symptoms of strangulation in the human subject resemble closely those just described as occurring in the dog.