The color of lividity depends on the color of blood and skin. China people's death spots are usually purple and carbon monoxide poisoning, because the blood contains a lot of bright red hemoglobin of carbon monoxide, so the death spots exposed through the skin are cherry red. Corpses that freeze to death and are poisoned by cyanide have more oxyhemoglobin in their blood due to insufficient use of oxygen in the body, so the lividity appearing through the skin is bright red. Bodies in water or frozen state are red or reddish because oxygen penetrates into subcutaneous blood vessels to form oxygenated hemoglobin. The charred body inhaled carbon monoxide before death, and the unburned part of the body was cherry red. When potassium chlorate and nitrite are poisoned, the lividity is grayish brown due to the formation of methemoglobin. White and black people have different skin colors, and the degree of corpse spots is also different. Black skin can mask the color of the corpse spot. With the development of changes after death, the dark purple-red of corpse spots gradually turned into light green, which blended with the color of corrupt corpses.
In the practice of forensic examination, it is often encountered that the corpse spot is mistaken for subcutaneous hemorrhage, which leads to disputes and needs identification.
Blood spots are dark red or blue-purple patches seen from the skin surface, which are caused by subcutaneous blood vessel rupture or hemophilia, hemorrhagic purpura, scurvy, septicemia and other diseases. In forensic examination, we must strictly distinguish between corpse spots and blood spots, which are two fundamentally different phenomena. Generally speaking, there are at least the following differences between corpse spots and blood spots. From the cause of formation, the corpse spot is formed by blood deposition, while the blood spot is formed by suppression; From the distribution position, the corpse spot is distributed in the lower and not oppressed parts of the body, while the blood spot can be formed in any part of the body; The boundary of the corpse spot is not clear, but the boundary of the blood is clear. Lividity can fade when pressed in descending and spreading periods, but blood stains will not fade when pressed at any time. The surface of the corpse spot shows exfoliation and swelling of the epidermis, while the blood spot is sometimes accompanied by violent injuries such as exfoliation and swelling of the epidermis. After the skin of the corpse is cut, the tissue is even purplish red, while there is coagulated or flowing blood in the blood spot skin or under the skin, and the boundary is clear. Microscopically, there is no tissue cell destruction in the corpse spot, but there is obvious tissue cell destruction in the blood spot.
With regard to the difference between corpse spot and blood spot or subcutaneous hemorrhage, Chinese classical forensic medicine has accumulated rich experience. This point has been discussed in the Record of Remembering Injustice for a long time, and there is an accurate identification method. It is recorded in the "Autopsy" section of the Record of Complaints: "You must use your fingers to examine injuries. If you press green and red, it means that the injury is hard. If it means that green and red are still together, it means that it is a real injury. If it is a change, it will point to a point, and the first finger is white. ..... hair change is the blood in human abdomen, which spreads after death and cannot be aggregated, so it is floating. The injury was beaten before death, and the blood gathered into injuries. " "Every dead person, behind his neck, back, ribs, arms and legs, ... his feet are red up and down, which is caused by his bleeding on his back, not other reasons." It is recorded in the section "Hanging": "After hanging, the blood is not good, and the body is purple and black, such as cloud condensation, and there is a change called blood barrier. There are bruises and edema, and the blood barrier is more or less. " Here, "hair change", "blood drop" and "blood barrier" all refer to corpse spots. Bright red corpse spots can be seen in: carbon monoxide poisoning (oxygenated hemoglobin), cyanide poisoning (oxygenated hemoglobin), freezing to death (oxygenated hemoglobin) and so on.
Gray-brown corpse spots can be seen in: nitrite poisoning, potassium chlorate poisoning (methemoglobin) and so on.
Nitrobenzene poisoning (methemoglobin) can be green-brown, which should be distinguished from corpse green.