口水

Saliva contains many useful components . Lubricants. Enzymes for breaking down food. And now,compounds that can reveal a person's age. That's according to a study in the journal Public Library of Science ONE. 唾液中含有很多的有用成分：润滑剂，分解食物的生化酶。而现在，发表在《公共科学图书馆·综合》期刊上的一项研究表明，这些成分还可以揭示一个人的年龄。  During normal development, DNA in your body gets what's called methylated . Small chemicals called methy! groups bind to the DNA, helping to determine which genes become active. But the patterns of methylation change as we grow older. Which was a clue that measuring methylation might give away age. 在正常的发育过程中，我们体内的DNA渐渐被甲基化[注1]。一些称为甲基的小化合物编进DNA中，用来决定哪些基因被激活。但是甲基化形式会随着我们的长大而改变。因此甲基测试也会泄露我们的年龄。  The researchers studied DNA in saliva contributed by 34 pairs of male identical twins, ages 21 to 55. They found 88 sites on the men's DNA where the amount of methylation correlated with their ages. The scientists next verified that finding in 60 men and women, ages 18 to 70. 研究人员对34对21至55岁男性同卵双胞胎唾液中的DNA进行分析。他们发现男性DNA上有88个地方的甲基数量与他们的年龄有关。于是科学家们接下来在18至70岁的60位男性和女性中去验证。  Then they narrowed in on two genes that had the strongest age-related correlation. And using just that data, they found that they could estimate the ages of their saliva contributors to within five years. 接着他们锁定在两组与年纪最为相关的基因上。利用这组数据，他们发现可以根据唾液来估计他们的年龄，误差在5岁之内。  This technique might help in crime scene investigations—recovered saliva could tell the age of a perpetrator. So if you're worried about anyone knowing how old you are, be careful where you spit. 这项技术在犯罪现场调查中可能会起到作用---被发现的唾液可以判断犯罪人员的年龄。所以，如果你担心别人知道你的年纪的话，喷口水的时候就要小心咯~