一只作证的苍蝇

∷王伟滨

不知不觉间，美剧《犯罪现场调查》CSI（Crime Scene Investigation）连续播出已有14年时间，在第十个年头上，法医昆虫学家（forensic entomologist） Gil Grissom终于离开警队，去密林深处找寻他的小虫们了。从那以后，CSI两次换主演，然而不论专业知识还是个人魅力，新人总难以企及 Grissom。老剧迷们明白，没有了Grissom和他时常摆弄的那些盛在瓶瓶罐罐中（学名叫vials，“玻璃瓶”）的小虫们，CSI 便失去了灵魂，几乎只剩下冰冷与血腥，于是，也便离曲终人散不远了。

这世界上，不知有多少人因为CSI而喜欢上了法医这门“学问”，我也算其中之一吧；当然，我只是停留在“喜欢”的层面，实则是个门外汉（layman）。不过，这份“喜欢”却带着我走进哈佛大学出版社出版于2000年的一本极为有趣的书——A Fly for the Prosecution（起诉）: How Insect Evidence Helps Solve Crimes。这书的主角是一群“让人尊敬”的小虫，作者是夏威夷大学昆虫学教授M. Lee Goff，此君从20世纪80年代开始，便担任檀香山警局的法医昆虫学顾问（Consultant in Forensic Entomology to the Medical Examiner of the City and County of Honolulu），算得上Forensic Entomology方面的权威人士。CSI 中的Grissom，从学识到“俏皮”（甚至Grissom从第四季开始留起的那有型的大胡子）与他都颇为相像；因此，读此君书，对于CSI 迷来说，自然有种特殊的亲近之感。

虽然由Harvard UP这样的顶级学术出版机构出版，但A Fly for the Prosecution并非艰深的学术著作，尽管各种昆虫的拉丁文名称的确令人头昏脑胀。这其实是一本颇为“安静”的书，虽然里面满是吓人的小虫的图示，就连各篇章的分割线也是由两条亲密的maggots（蛆）组成。说它“安静”，是因为，它会让你感到一种“超脱生死”的愉悦，更会给你一种因自然界中“小生命”的伟大和“真诚”而产生的欣喜。

若要涉足Forensic Entomology，首先需要转变对于死亡的看法——在自然界，万物都是cycling与recycling过程中的某个节点，而“小虫们”则是这个过程中的催化剂：

“Anyone involved in death investigations quickly becomes aware of the connection between dead bodies and maggots. Insects are major players in nature’s recycling effort,and in nature a corpse is simply organic matter（有机物）to be recycled. Left to its own devices（任其自然）, nature quickly populates a corpse with a diverse community of organisms, all dedicated to reducing the body to its basic components. Very quickly, ‘worms’ appear,crawling out of the various orifices（孔口）”。

小小的蛆虫，千百年来，总被人类认为是“讨厌”、甚至“可怕”的东西，它们的存在似乎只是证明了生命的脆弱和尘世的肮脏。在Charles Baudelaire（波德莱尔）的Les Fleurs du mal（《恶之花》）中，有一首名为《腐尸》（“A Carcass”）的诗，这样描写道：

Recall to mind the sight we saw, my soul,That soft, sweet summer day:

Upon a bed of flints（燧石）a carrion（腐尸）foul（污秽的）,

Just as we turn’d the way,

...

The sky regarded as the carcass proud

Oped（opened古体写法） flower-like to the day;

The flies the putrid（腐烂的） belly buzz’d about,

Whence black battalions（部队）throng（拥挤）

Of maggots, like thick liquid flowing out

The living rags along.

And as a wave they mounted and went down.

Or darted（猛冲）sparkling wide;

As if the body, by a wild breath blown,

Lived as it multiplied.

...

Yet you will be like that corruption too,

Like that infection prove—

Star of my eyes, sun of my nature, you.

My angel and my love!

...

（Translated by Richard Herne Shepherd）

爱人，想想我们曾经见过的东西，

在凉夏的美丽的早晨：

在小路的拐弯处，一具丑陋的腐尸

在铺石子的床上横陈

……

天空对着这壮丽的尸体凝望，

好像一朵开放的花苞

苍蝇嗡嗡地聚在腐败的肚子上，

黑压压的一大群蛆虫

从肚子里钻出来，沿着臭皮囊，

像黏稠的脓一样流动。

这些像潮水般汹涌起伏的蛆子

哗啦哗啦地乱撞乱爬，

好像这个被微风吹得膨胀的身体

还在度着繁殖的生涯。

……

可是将来，你也要像这臭货一样，

像这令人恐怖的腐尸，

我的眼睛的明星，我的心性的太阳，

你，我的激情，我的天使！

……

（钱春绮 译）

残酷的诗人向身边的爱人宣称，路边的腐尸也是美丽的她难以摆脱的归宿，只有不朽的诗篇可以保存“爱的形姿和神髓”（I have kept the godlike essence and the form / Of perishable bliss!）。

即便是经常与小虫们打交道的法医，也往往只是厌恶地把它们冲刷干净，而没有意识到除了把尸体“蹂躏”得一塌糊涂之外，它们还能有什么作用。韩愈在《马说》开篇感叹道，“世有伯乐，然后有千里马。千里马常有，而伯乐不常有。”世间的一切事物同是这个道理——这世界上并不缺少有价值的东西，但缺少有价值的眼睛。对于小虫们来说，forensic entomologist便算得上它们的伯乐了。

有时，我们不能不感叹，对于自然的奥秘，人类所知不仅甚少，而且也是甚晚的。长期以来，人们一直以为蛆虫是原本存在于人或动物体内的，在活体死亡之后，便从体内钻出来，吞吃尸体。今天，在中国的某些地方，人们还把腊肉上的“小虫”，称作“肉芽”，大概认为那些小东西是像豆芽一样，从肉里钻出来的呢。在西方，直到1668年，意大利医学家Francesco Redi才通过实验证实，蛆虫与蝇卵（ fly eggs）之间是存在直接联系的。

不过，像很多重大科学发现一样，倒是中国人很早便在法医昆虫学方面有了建树。据Lee Goff说，“大宋提刑官”宋慈便是Forensic Entomology的先驱之一：“In 1235，a Chinese“death investigator”named Sung Ts’u（宋慈）wrote a book entitled The Washing Away of Wrongs（《洗冤集录》）, which was translated into English by B. E. McKnight in 1981. Sung tells of a murder in a Chinese village in which the victim was repeatedly slashed（砍）. The local magistrate（地方法官） thought the wounds might have been in flicted（造成）by a sickle（镰刀）. Repeated questioning of witnesses and other avenues（途径） of investigation proved fruitless. Finally, the magistrate ordered all the village men to assemble（集合）, each with his own sickle. In the hot summer sun, flies were attracted to one sickle, because of the residue（残留）of blood and small tissue（组织）fragments still clinging to the blade and handle. Confronted with this evidence, the owner of the sickle confessed to the crime. The magistrate’s action demonstrates considerable knowledge of the activity patterns of the flies, which were certainly blow flies（丽蝇）”。此外，有关昆虫在断案中的重要作用，《洗冤集录》中另有多处提及，足见宋提刑在此领域的洞见。

今天，forensic entomologists与他们信赖的小虫们对于探案的最重要贡献是“确定死亡时间”（to determine the time since death, the postmortem interval)。此领域的有两位奠基者——Bernard Greenberg和Jerry Payne。前者关于多种丽蝇的生物和生命周期（the biology and life cycles）的研究为辨识小虫们的“年龄”提供了依据。而后者提出的“succession”（接续）理论，则为辨识小虫们来到的先后次序指明了道路。“Simply stated, succession is the idea that as each organism or group of organisms feeds on a body, it changes the body. This change in turn makes the body attractive to another group of organisms, which changes the body for the next group, and so on until the body has been reduced to a skeleton. This is a predictable process, with different groups of organisms occupying the decomposing body at different times”。于是，结合二人的理论，forensic entomologist便可以让小虫们说话，判定死亡时间了。

1996年11月，在夏威夷某地（时间与地点是识别小虫的关键）一片甘蔗地中发现一具“分解状态”的（decomposed，常译作“腐烂的”，但从尊重小虫们和死者的角度来看，称为“分解状态的”似乎更合适，因为生命形态本就是compose与decompose两面）女尸。在分析了于抛尸地采集的各类小虫后，Lee Goff断定死亡时间为样本(specimen)采集前的34天。据此，警方锁定了最后与死者接触的人，并获得搜查证（search warrant）；在仔细搜查了曾经嫌犯细心清理的住所后，警方最终通过luminol(发光氨)技术发现了大量血迹：“When luminol was sprayed（喷洒）in the bedroom and the lights were dimmed（调暗）, the outline of a body was clearly visible on the floor beside the bed. The body had been lying on its side and blood had seeped（渗出）out of it to form the outline”。显然，若非小虫们“作证”，警方便难以锁定嫌犯，更无法得到搜查证，冤案便不知如何昭雪了。

有时候，小虫们提供的线索远比“死亡时间”更有趣。1992年8月27日，在Grand Canyon（大峡谷）的某个山崖下发现了一对男女的遗体，尸体解剖证实，二人是在一处沙漠地带溺水死亡（The results of the autopsies indicated that both had died by drowning, even though the bodies had been recovered in a dry, desert area），这结论当然不可思议，除非，你假设他们是溺水而死后，又被人捞起，然后抛尸他处。然而，Lee Goff分析了现场小虫的样本，以及当地土壤样本后，得出结论：“It appeared that the two hikers, last seen alive on August 18,had left the marked trail（有标志的路线） through the canyon. The woman had fallen, injuring her leg.Her companion then climbed down to assist her and fashioned（制作） the crude（简陋的） splint(夹板）.Because of injuries or oncoming darkness, they found themselves spending the night of the twenty- first on the canyon floor. During the evening, a flash flood(骤发山洪）swept through the canyon, drowning them both, and depositing their bodies downstream, 100 feet apart on rocks at the base of a cliff. As is typical in flash floods, the water evaporated quickly（蒸发）,leaving no trace. With daytime temperatures ranging from 81 to 100 ℉, their clothing quickly dried and insects immediately began to arrive at the bodies.Thus they were discovered five days later, having drowned in a desert”。

与蛆虫和尸体整日为伍，大概要算得上一份真正意义的“dirty job”了吧。不过正如Lee Goff所说，“As forensic entomology has changed, I also have changed... I am no longer concerned with just the insects and what they do to each other. I have entered into an area where insects, crime, and our criminal justice system intersect with（交叉）very darkest aspects of human nature.” 被Lee Goff亲切地称作“witnesses”（证人）的小虫们不会撒谎，不会爽约，它们总是在该“到场”的时候“到场”；与这些“可爱”而“单纯”的creepy-crawlies（爬虫）相比，反倒是“人”让昆虫学家难以理解了：在很多的案件中，案发地附近，甚至当场，便有不止一个目击“证人”，但是这些人既没有出面制止犯罪，也没有站出来在法庭上指证罪犯。“I find myself looking again at old questions regarding human nature. Some things I am certain I will never be able to comprehend”。也许，在良知的法庭上，小虫们也是指证我们的证人吧。