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The smell of death：The dogs have had their day

来源：网络发布时间：2009-08-25

　　IT IS morbid, but true, that one of the ways survivors of natural disasters are found is by bringing out bloodhounds that have been trained to find the dead. Often, when these dogs reveal corpses under rubble, rescuers also find previously undetected air pockets with living people in them. Dogs are useful when police officers are looking for the buried corpses of murder victims, too. Such animals, however, require feeding and housing when they are not being used, and expert handling when they are. It might be better, therefore, if they could be replaced by machines—and that is what Sarah Jones and Dan Sykes of Pennsylvania State University propose to do. As they outlined to this week’s meeting of the American Chemical Society, in Washington, DC, they have been analysing the smell of corpses, with a view to automating the process of detecting them.
　　The idea of doing this is not entirely new, but when Ms Jones and Dr Sykes looked at the previous studies they found that the corpses used were usually at least three days old. That is an almost inevitable delay if human cadavers are employed, since permission must be sought and forms filled in. But the two researchers wanted to know which chemicals emanate from freshly dead bodies, as well as from those that have been around for a few days. So they decided to compromise and work on pigs instead of people. Pigs are often used as substitutes for humans in early-stage medical experiments, as they are about the same size. For that reason, too, they decay at the same rate and go through the same phases of decomposition.
　　To carry out their experiment Ms Jones and Dr Sykes put dead pigs inside small wooden chambers that were covered with clear plastic sheets. The chambers, which were placed in the middle of a field, prevented large scavengers from coming along and dragging the corpses away. Insects and bacteria from the air above and the grass below, however, had easy access to the bodies.
　　The chemicals of decay were sampled by three collectors inserted through holes in the plastic sheet. The collectors contained fibres of different compositions, each of which absorbed a unique range of volatile molecules such as organic acids, alcohols, amines and ketones. The fibres were replaced at regular intervals over the course of seven days and taken away for analysis by a device called a gas chromatograph-mass spectrometer.
　　As Ms Jones and Dr Sykes told the meeting, the composition of the chemicals released by the corpses did, indeed, change over time. Acids made up 32% of the compounds detected in the first two days, but dropped to 25% after the third day. Some of the individual acids that were released, such as pentanoic and benzoic acid, were present throughout all seven days that the experiment was conducted. Some, including tetradecanoic acid, were found early but not late in the decomposition process, while others, such as acetic and propanoic acid, were found late but not early. Similar results were found with other sorts of volatile compounds.
　　This information will be useful for establishing “time of death” in murder investigations. It could also be used to fine-tune an electronic nose, if such a device were to be used at the site of a disaster. Electronic noses rely on detecting changes in the electrical conductivity of various substances when they absorb particular target molecules, and could easily be brought in to replace dogs if they were thought reliable enough.
　　For that to happen, more research will be needed. The pigs will have to be staked out in a wide variety of environments, and more experiments on human corpses would be desirable, as well. The result, though, could be lives saved and murderers caught—as well as a few redundant bloodhounds.

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