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Physically Altered BloodstainsDrying time of BloodThe drying time of blood is a function of thebloodstain size and volumethe nature of the target surface and The influences or effects of the external environment.

It follows that humid environments, lower temperatures and minimal air flow will produce longer drying timesThe drying time of blood in general is decreased by increased temperature and decreased humidity, the presence of significant air currents such as wind and the effect of a fan.Surfaces which permit the soaking of blood into the material may produce significantly longer drying times.The drying of bloodstains is observed initially around the edges or periphery and proceeds inward to the central portion of the stain. Occasionally the dried central area of a dried bloodstain will flake away leaving an intact circular rim.A useful observation of bloodstains on surfaces other than horizontal is the recognition of the dense zone. When a blood droplet of sufficient volume strikes a nonhorizontal surface, gravitational forces continue to act upon the liquid portion of the bloodstain. The lower area or base of the bloodstain will be more dense due to the continued accumulation of blood. After the bloodstain has dried sufficiently on the surface, this dense zone cannot be alteredClotting of BloodA blood clot is formed by a complex mechanism involving the plasma protein fibrinogen, platelets, and other clotting factors. It is observed visually as a network of fibrous material (fibrin and red blood cells). Subsequently, the blood clot begins to retract causing a separation of the remaining liquid portion which is referred to as serum (Figure 4.4). Blood clots and serum stains surrounding them as well as the degree of observed drying of blood should be recognized as important information at crime scenes. Occasionally, events take place after blood has been shed and has begun the clotting process.Bloodstain patterns produced by partially clotted or clotted blood indicate a time interval between the bloodshed and the activity producing the pattern.The Aging of BloodstainsAs bloodstains increase in age, they progress through a series of color changes from red to reddish brown to green and eventually to dark brown and black.This change of color is attributable to alterations in the hemoglobin of the blood.A particular environment and especially the presence of bacteria and other microorganisms will affect the sequence and duration of color changes in bloodstains.Other Alterations of BloodstainsThe deposition of bloodstains at crime scenes occurs under many environmental and physical conditions that may alter their appearance either initially or thereafter.Diluted bloodstains may be present at scenes where excessive moisture is present such as external environments involving rain or snow and the characteristics of the original stains may be altered to the point where interpretation is difficult or impossible. Diluted bloodstains may be encountered at crime scenes due to mixture with water or other fluids.The alteration of bloodstains as the result of the effects of heat, fire, and smoke is another consideration for interpretation. In some cases bloodstains may be covered by soot and be missed entirely at the scene of a homicide that preceded a fire. In many cases where soot is deposited over bloodstains on a surface such as a wall, the bloodstains may appear darker than the surrounding soot covered surface and lend themselves to interpretation.Bloodstains undergo a variety of physical changes depending upon their proximity to sources of heat, fire, and smoke.Bloodstains may darken, fade (ghosting effect) or be totally destroyed depending upon the intensity and duration of a fire.It is also important to recognize alterations to bloodstains at fire scenes that may occur due to effects of water and the activities of fire fighting personnel.