By Jean Balchin 31/05/2017


Decapitated pig’s heads floating in the moonlit water may sound like a scene from a B-grade horror movie, yet Gemma Dickson’s investigation into the microbial marine decomposition of human and animal remains has revolutionised forensic science.

This may come as a surprise, but currently, if human remains wash up on shore, there is no established scientific method to conclude how long the body has been in the water. Moreover, given that our country is surrounded by coastline, a great number of accidental and suspicious deaths occur at or around the sea. Bodies in seawater are at the mercy of a variety of decompositional factors which depend on the remains themselves and the specific marine environment.

Pigs Heads

Marine bacteria appear to play an integral role in marine decomposition, though this process is poorly understood. Dickson set out to investigate whether the types of marine bacteria inhabiting a dead body changes as it decomposes. If so, these bacteria serve as a postmortem clock and indicate the length of time a body has been submerged in the ocean. Pigs (Sus scrofa domesticus) and humans are remarkably similar, sharing hairless skin and a thick layer of subcutaneous fat as well as other traits. To this end, adult pigs’ heads were used as an analogue for human cadavers and were plonked into the Otago Harbour and the Wellington Harbour for up to three weeks, or until they were reduced to a bare skull. Dickson sampled the bacteria in the decaying soft tissue every two or three days.

In order to measure the effect of water temperature on bacterial colonisation, the pigs heads were submerged in autumn, early winter and late winter. A microbial biofilm developed on the submerged remains, and a largely DNA-based, molecular approach was taken in order to explore the diversity of this bacteria. The complementary methods of phylogenetic analysis of cloned 16S rRNA gene sequences and T-RFLP profiling of bacterial community composition were applied. Temperature did indeed affect the colonisation of bacteria. For the heads submerged in winter, Psychromonas bacteria colonised during the first stages of decomposition, while specific Bacteroidales genera only colonised after ten days of submersion. Dickson’s findings thus enabled the creation of a characteristic profile of bacterial genera that could be established to infer time of entry into the water.

Sydney Smith

Interestingly, when it comes to decomposed bodies and water, New Zealand has paved the way before. Forensic science pioneer Sir Sir Sydney Smith (1883-1969) from little old Roxburgh achieved world renown by reading the stories of dead men. Smith’s forensic science changed the way crime was investigated and solved. Smith’s journey into the world of forensic science began in a medical faculty in Edinburgh. Edinburgh has long been regarded as an important centre for the study of forensics, carrying on a tradition that had emerged in France and Germany. The Professor of Medical Jurisprudence in Edinburgh was more often than not the Chief Surgeon to the City Police. And who could forget that one of the early members of the faculty, Dr Bell, was actually the inspiration for the most famous detective of all time – Sherlock Holmes.

The Hopetoun Murder

Medico-legal experts specialise in forensic medicine and are employed by the police to examine dead bodies in order to determine the cause and manner of death. To quote Smith himself, only the motive “lies outside the professional scope of the medico-legal expert, and in certain cases, such as murder after sexual assault, he or she may be able to explain this too.” In 1913, the bodies of two young boys were discovered in the Hopetoun quarry near Edinburgh. Although the bodies had been submerged in water for at least eighteen months, Smith was able to deduce a significant amount of information, including the length of time before their deaths the two boys had eaten their last meal; a meal of  Scotch broth about an hour before they were murdered. He also deduced that they must have walked to the quarry and conjectured that they must have been killed by someone they knew. The bodies were barely recognisable, and had been largely converted into a substance called adipocere. Adipocere is a wax-like organic substance formed by the anaerobic bacterial hydrolysis of fat in tissue, such as body fat in corpses. In its formation, putrefaction is replaced by a permanent firm cast of fatty tissues, internal organs, and the face. Smith’s evidence led to the arrest of the children’s father, Patrick Higgins and he swung on the scaffold.

Rather disturbingly, Smith stashed away the heads of both children, an arm and a leg from each of them, and all their internal organs. The specimens were installed in the Forensic Medicine Museum at Edinburgh University and employed as teaching examples of advanced adipocere. In January 2008, the university agreed to return the remains, if the claimant could establish her relationship and the other relatives all agreed. I have a sneaking suspicion that I must have walked past the sad remains of these poor children, while perusing the Surgeon’s Museum in Edinburgh. Row upon row of preserved limbs stuffed ignominiously in glass jars greeted me as I wandered around the museum one day while on my student exchange. There’s something about the casual display of these young boys that disturbs me greatly, and I hope one day they rest in peace.


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