Page 14 - Science Focus (Issue 018)

The biggest advancement the facility made is in our understanding in the difference in the decomposition
understanding of post-mortem changes, or the various process in different environments.
processes that occur in a body after death. As anyone
who has accidentally left a pork knuckle outside in a Other than serving as an active research site for post-
warm summer afternoon can testify, dead body tissues mortem changes and human skeletal studies, the Body
undergo a series of grisly changes that usually culminate Farm also provides training courses on forensic recovery
in complete skeletonization . The three most noticeable techniques for FBI investigators, law enforcement workers
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early changes after death are algor mortis, rigor and forensic pathologists. The subject matter of the Body
mortis and livor mortis. Shortly after death, our bodies Farm, while unorthodox, is of great importance to us,
stop producing heat and gradually cool to the room and for its recent advancements, we must thank not only
temperature (algor mortis). A few hours later – the exact the researchers involved but also the contribution of the
time depends on a variety of factors – once cellular selfless donors who bequeathed their bodies to science.
energy (ATP) runs out, muscles could no longer return to
a relaxed state, leading to the stiffening of limbs (rigor 1 The decomposition progress may be incomplete in rare
mortis). Gravity also causes blood to settle into the lower circumstances. In 1991, hikers on the Ötztal Alps stumbled
parts of the body, leading to reddish-blue discolorations upon a frozen corpse which turned out to be over 5300
2
years old. The glacier mummy, who is now called "Ötzi" the
alternating with pallid areas where blood is drawn away iceman, was covered in ice shortly after his death, which
(livor mortis). halted the decomposition process such that his hair, organs
and even his clothing and equipment were left intact [6].
What else could be going on? As organismal (You may learn more about Ötzi from the cover story of
homeostasis fails, individual cells would begin to Science Focus Issue 002.)
digest themselves. Microbes from the gut and outside 2 In cases of poisoning, the color might be different [7].
the external orifices could also migrate and multiply
throughout the corpse and digest bodily tissues
(putrefaction). Combined, they lead to the liquefaction
of body organs and the build-up of a cocktail of gases 手放在戶外，就能見證身體組織在死後經歷一連串的駭人
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that lead to the characteristic stench of cadavers. The 變化，通常直至完全化骨為止 。死後初期的三個明顯現象
build-up of internal pressure leads to external changes 為：屍冷（algor mortis）、屍僵（rigor mortis）和屍斑（livor
including, among others, abdominal bloating, skin
blisters, and discharge of liquid from body orifices. mortis）。死後，我們的身體會停止產生熱能，並慢慢冷卻
Scavengers such as blowflies, vultures and raccoons 至室溫（屍冷）。數小時後 — 具體時間受不同因數影響 —
may be attracted by the stench to feast on the 當細胞剩餘的能量（ATP）被消耗殆盡後，肌肉再不能回到
decaying body. Eventually, after the soft tissues have
been decomposed, dried up or eaten, only skeletons 鬆弛的狀態，導致四肢僵硬化（屍僵）。受重力影響，血液
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remain. 會積聚在身體的低處，令皮膚出現紫紅色的斑痕（屍斑），
當中又穿插著的一些因為血被抽走而變得蒼白的區域。
These processes form a rough timeline which we
may use to determine the post-mortem interval (PMI),
or the time elapsed since an individual died. This is 還會有甚麼事情發生？在身體不能維持體內平衡之時，
of great importance to criminal and archaeological 個別細胞會開始分解自己。消化道內和身體孔竅外的微生
investigations, but a precise estimation of the interval 物也能遷移至並在身體內外迅速繁殖，分解身體組織（腐
is confounded by a range of variables. The most
important factor is temperature, which influences the 爛）。這兩個過程導致器官液化，亦令體內累積不同氣體，
rate of biochemical reactions and the activity level 形成腐屍獨特的惡臭氣味。內部壓力增加也會導致不同外
of microbes and scavengers. Humidity also plays an 部變化，例如腹脹、皮膚水泡、身體孔竅流出液體等。諸如
important role, as water serves as an essential medium
for biochemical reactions and to sustain the survival 綠頭蒼蠅、禿鷲和浣熊等的食腐動物可能會受屍臭吸引而
and growth of microbes and scavengers. Using their 前來享用腐屍。最終，當軟組織分解、乾涸，或被吃光後，所
database of hundreds of decompositional events of the 剩下的也只有骨骼。
human body, researchers at the Body Farm were able
to derive an empirical formula that relates the extent
of decomposition, temperature and humidity to PMI 這一連串過程可以被拼湊成一條粗略的時間線，讓我們
[4]. The formula is, however, incomplete: adjustment is 可以窺探死後間隔時間（post-mortem interval/PMI），
needed if the formula is applied to other regions with 也就是死者由死亡一刻距今的時間。PMI 對於刑事或是考
different soil quality and climate. Researchers at the
facility have also been investigating other methods, such 古調查固然重要，但要準確預測 PMI 需要考慮許多變數。
as analyzing the chemical content of decomposing 溫度是最重要的因數，它能夠控制生化反應的速率，以及
body tissues or the surrounding soil environment, to 微生物和食腐動物的活躍程度。濕度也是重要的變數，因
support the determination of the PMI [5]. The studies are
also replicated in several other similar facilities in the US, 為水是生化反應中不可或缺的介質，又是維持微生物和食
Canada and other countries in order to improve our 腐動物生命和生長的必需物質。參考研究中心資料庫中數