Haemotaphonomy

Haemotaphonomy or hemotaphonomy (from the Greek haima for blood, taphos for burial, and nomos for law) is the study of bloodstains, and especially of the changes in appearance and size of the cellular components, as well as the characteristics of their cell position and appearance in function of the superficial topography and composition of the substrate. This science was founded by the Catalan biologist Policarp Hortolà, who in 1992 used for the first time the term 'hemotaphonomy' to refer to his cytomorphological researches on red blood cells in bloodstains.

Historical antecedents of haemotaphonomy
The most abundant of the blood corpuscles (the red blood cells) were yet observed during the last half of the 17th century by early optical microscopists, such as Giovanni Alfonso Borelli, Jan Swammerdam, Marcello Malpighi and Anton van Leeuwenhoek. The occurrence of (at least cytomorphological) preservation of anucleate, mammalian red blood cells in bloodstains has been reported even in Olduwan palaeolithic tools from Sterkfontein Cave (South Africa), assigned to be ca. 2 Ma old, at the boundary between the Pliocene and the Pleistocene epochs. These corpuscles have also been identified in prehistoric immovable items, such as an early Holocene building at Çayönü Tepesi (Turkey), containing anucleate red blood cells, human immunoglobulin G (IgG) and both human and non-human haemoglobin (Hb) on a stone slab.

Some epistemological principles of haemotaphonomy
The presence of all kind of residues on implements agrees with the criminalistic well-known Locard’s Principle of Exchange ('every contact leaves traces'). On the other hand, experimental palaeontology (actuopalaeontology) and experimental archaeology are both based upon the Lyell’s Principle of Actualism ('the present is the key to the past'). A short-time preservation of specimens is a sine qua non precondition to do feasible a (palaeobiological, bioarchaeological, forensic) longer one. Also, in forensic analysis the presence of RBCs in a smear is considered a blood confirmation. Therefore, the study of the different erythrocyte and plasma-matrix morphologies exhibited in bloodstains represents a field with applications to forensics, prehistoric archaeology, and palaeoanthropology.

Vertebrate blood
Vertebrate blood (i.e., blood sensu stricto) is a cell suspension into a fluid medium (the plasma). In this histological tissue, three types of cells are present: erythrocytes (red blood cells, RBCs), leukocytes (white blood cells, WBCs) and thrombocytes (platelets, in mammals). Unlike the other vertebrates, mammals have anucleate RBCs (erythroplastids or akaryocytes). As an exception, the slender salamanders (family Plethodontidae, order Caudata, class Amphibia) have some proportion of anucleate RBCs, with Batrachoseps attenuatus (Eschscholtz, 1833) possessing nearly 95% erythroplastids. Also, the pearlside teleostean fish Maurolicus mülleri (Gmelin, 1789) (family Sternoptychidae, order Stomiiformes, class Actinopterygii) has anucleate erythrocytes.

Mammalian RBC morphologies in the body and in the smear
Due to the lack of nucleus, the typical mammalian RBCs are shaped as biconcave discs (discocytes). This does not apply to the family Camelidae, where RBCs are oval (ovalocytes). Other physiological shapes, which are minor or pathologic, are: echinocytes (burr or berry cells), dacryocytes (tear drop cells), schizocytes (helmet cells), keratocytes (horn cells), drepanocytes (sickle cells), and many others. The largest part of the smear-origin RBC shapes share morphology with those described in haematology. But two time-independent RBC shapes are due specifically to blood drying phenomena. So they are considered as genuine RBC morphologies characteristic of mammalian bloodstains, not found under physiological conditions. These shapes are moon-like shapes or hecatocytes (related to erythrocyte-plasma interaction when drying), and negative replicas or janocytes (related to imprinting by dried plasma matrix).



The role of membrane in the erythrocyte morphology
The RBC morphology is encoded in the mechanical properties of its composite membrane. This composite membrane is composed of a plasma membrane plus a membrane skeleton. The plasma membrane contributes bending rigidity, and the membrane skeleton contributes stretch and shear elasticity. The RBC plasma membrane is the lipid bilayer containing proteins such as ankyrins, band 3, and glycophorins. The erythrocyte membrane skeleton, which is localized exclusively on the cytoplasmic surface of the plasma membrane, is a network of proteins, mainly spectrins, actins, and band 4.1.

Influence of the smear substrate and ageing in erythrocyte morphology in bloodstains
From the haemotaphonomical point of view, the concrete type of bloodstain substrate (stone, metal, paper...), whether of similar physical properties, do not seems to play a dramatic role in RBC morphology. The most significantive bloodstain substrate physical properties would be grouped into three categories: (i) those related with the degree of thickness homogeneity of the smear by the forming of thicker/thinner subareas (topography), (ii) those related with the mechanical seizing and/or breaking of the cell fraction by surface microcrystals while smearing, and with the adherence of the whole blood to substrate while drying and/or ageing (roughness and texture), and (iii) related with the infiltration of blood (mainly plasma) into the substrate (permeability, its related absorbency, and permeability-influencing fissuration). On the other hand, the high RBC preservation exhibited in the samples when examined under a scanning electron microscope seems to indicate that dried blood tissue is homologous or at least analogous to a mummified one. Therefore, it is not expected that the ageing time span be determinant per se of the degree of bloodstain preservation.

Other external links

 * Poikilocytosis: abnormalities of erythrocyte shape
 * Organization of the erythrocyte membrane
 * Erythrocyte size database
 * Red gold: the epic story of blood