How the microscopic structure of a cat’s tongue helps keep its fur clean
T.S. ELIOT’S MYSTERY cat, Macavity, besides being a criminal mastermind able to evade the combined ranks of British law enforcement, had a coat that was “dusty from neglect”. Criminality is one thing, but this truly strains the imagination. Real cats are champion groomers.
Of the ten hours a day that a domestic cat deigns to remain awake, it spends a quarter licking dirt, fleas, blood and loose hairs from its fur. Cats’ tongues, specialised for this task, are covered in hundreds of backward-facing keratin spines. But exactly how these cone-shaped protuberances, called filiform papillae, work to give the animals such mastery over their cleanliness has remained unknown until now.
To crack the mystery Alexis Noel and David Hu, a pair of engineers at the Georgia Institute of Technology, in Atlanta, examined the grooming mechanisms of six feline species—from domestic pets and bobcats to snow leopards and lions. Studying the activity of tongues inside the mouths of living creatures proved tricky, so instead Dr Noel and Dr Hu built an automated grooming machine fitted out with tongues and furs from animals whose lives had ended at places such as the Tiger Haven in Tennessee, a sort of retirement home for rescued big cats. They attached the tongues to a mechanical arm and made them “lick” the furs. High-resolution cameras and scanners took pictures.
为了解开谜底，亚特兰大佐治亚理工学院的工程专家亚历克西斯·诺埃尔（Alexis Noel）和胡立德（David Hu）探究了家猫、短尾猫、雪豹和狮子等六种猫科动物的清洁梳理机制。研究活体动物的舌头在口腔内的活动难度太大，所以两人打造了一台自动梳理机，装上了猫科动物的舌头和皮毛。这些器官的主人已经在田纳西州的老虎安息所（Tiger Haven）等收容大型猫科动物的养老院里去世。两人把舌头装到机械臂上，让它们去“舔”毛皮，并用高分辨率相机和扫描仪拍下照片。
The two researchers found that the filiform papillae were shaped not, as had previously been thought, like solid cones. Rather, they resembled tiny scoops. Each had a small groove—named a cavo papilla by the team—at its tip.
This structure permits surface tension to wick saliva from a cat’s mouth and release it into the farthest recesses of the animal’s fur. During each lick, about half of the saliva on the tongue is so transferred. Saliva serves as a multi-purpose cleaning agent and the cavo papillae also assist the absorption, for the return journey, of any dirt or blood that needs removing. The cat’s tongue therefore “acts like a loofah and a sponge at the same time”, says Dr Hu.
The pair’s findings, just published in the Proceedings of the National Academy of Sciences, could inspire new ways to clean complex hairy surfaces. The authors themselves demonstrated one such application, which they call the tongue-inspired grooming (TIGR) brush. To make this they employed 3D printing to create structures, shaped like cat papillae, attached to a silicone base. The TIGR brush pulled on cat hairs and fur with less force than existing brushes, and was easier to clean. Such a brush could also be used to spread medicines deep into a cat’s fur or onto its skin, without the usual distressing practice of having to shave the animal first.
两人的研究结果刚刚发表在《美国科学院院刊》上，可能会启发人们研究出清洁复杂多毛表面的新方法。两位研究人员自己展示了这类应用的一种，他们称之为TIGR刷（Tongue-inspired Grooming brush，即“仿猫舌清理刷”）。他们用3D打印制造出形似猫舌乳突的结构，嵌在硅胶基垫上。TIGR刷梳理猫毛时拉扯猫皮毛的力度比现有的刷子更轻，也更容易清洁。这种刷子还可以将药物涂抹在猫的皮毛深处或皮肤上，也就避免了通常需要先剃掉猫毛这个叫人烦恼的操作了。
（Nov 24th 2018）