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Stingray injury
Stingray injuries are caused by the venomous tail spines or stingers of rays in the order Myliobatiformes, most significantly those belonging to the families Dasyatidae, Urotrygonidae, Urolophidae, and Potamotrygonidae. Stingrays generally do not attack aggressively or even actively defend themselves. When threatened, their primary reaction is to swim away. However, when attacked by predators or stepped on, the stinger in their tail is whipped up. This is normally ineffective against sharks, their main predator.〔(【引用サイトリンク】 Stingray City - About Stingrays )〕
Depending on the size of the stingray, humans are usually stung in the lower limb region. Stings usually occur when swimmers or divers accidentally step on a stingray,〔 but a human is less likely to be stung by simply brushing against the stinger. Surfers and those who enter waters with large populations of stingrays have learned to slide their feet through the sand rather than taking steps, as the rays detect this and swim away, as will stamping on the bottom as one treads through murky water. .〔http://uk.news.yahoo.com/5/20091116/twl-croc-hunter-s-widow-blamed-for-bushf-3fd0ae9.html〕 The stinger usually breaks off in the wound.〔 This is not fatal to the stingray as it will be regrown at a rate of about per month (though with significant variations depending on the size of the stingray and the exact species). Contact with the stinger causes local trauma (from the cut itself), pain, swelling, and muscle cramps from the venom, and possible later infection from bacteria〔 or fungi. Immediate injuries to humans include, but are not limited to: poisoning, punctures, severed arteries and veins, and occasionally death.
Fatal stings are very rare, but can happen, famously including Steve Irwin. In this case, the stinger penetrated the thoracic wall, causing massive trauma.
== Biological structure of the barb ==
The barb is covered with rows of sharp flat spines, composed of vasodentin. Vasodentin is an incredibly strong cartilaginous material which can easily cut through flesh. The undersides of the spines contain two longitudinal grooves which run along the length of the spine and enclose venom-secreting cells. Both the venom-secreting tissues and vasodentin are enveloped in an epidermis that tears open when the barb is plunged into a victim. Some spines may break off as the barb exits the wound and stay within the victim causing prolonged envenoming.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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