托福各单项备考是相互联系的，托福听力和托福阅读作为语言学习中偏向于输入的部分，可以有效积累重要语料素材助力作为输出部分的托福口语和托福写作能力提升。在备考托福阅读的过程中我们可以通过扩展英文文章阅读去辅助阅读和其他各单项能力的提高，积累地道英文表达，提升语感和熟练度。下面我们看一篇经济学人双语阅读文章：对抗衰老。
Fighting ageing
Youthful spirits
Blood transfusions from young animals can revitalise old ones. Trials are now running to see if that is true for people, too
对抗衰老
青春血液
输入年轻动物的血液可助年老动物重现活力。在人类身上是否亦是如此?试验正在进行中
IT WAS one of the oddest experiments in the history of dentistry. In the early 1950s a researcher called Benjamin Kamrin was looking into the causes of tooth decay. To do so, he turned to that scientific stalwart, the lab rat. Specifically, he cut small patches of skin from pairs of rats and then sutured the animals together at the site of the wound. After about a week of being joined in this way, the animals’ blood vessels began to merge. The result was two rats whose hearts pumped blood around a shared circulatory system. This state of affairs is called parabiosis.这是牙科史上最怪异的试验之一。20世纪50年代初，一位名叫本杰明·卡姆林(Benjamin Kamrin)的研究人员为研究蛀牙的成因，求助于科学试验的忠实伙伴——大鼠。具体来说，就是从好几对大鼠身上分别切下小块的皮肤组织，然后在切口处把这些大鼠两两缝合在一起。如此合体约一周后，它们的血管开始融合。结果是两只大鼠的心脏会向共享的循环系统供血。这种情况被称为联体共生(parabiosis)。
Parabiosis works best on animals that are closely related genetically. By getting his rats to share blood, as well as genes, and then feeding the animals a variety of diets, Kamrin hoped to prove (which he did) that it was sugar in food, and not some inherent deficiency in individuals, that was responsible for rotting their teeth.在基因密切相关的动物身上，联体共生的效果最佳。卡姆林让这些大鼠共享血液和基因，然后向它们投喂各种食物，希望以此证明导致龋齿的是食物中的糖分，而非个体的某种先天不足。他最终成功证明了这一点。
Other people, though, have used the technique to find more striking results. For example, mammalian bone density usually drops with age. Three years after Kamrin’s work, however, a gerontologist called Clive McCay showed that linking an old rat to a young one boosted the density of the oldster’s bones. In 1972 another paper reported, even more spectacularly, that elderly rats which shared blood with young ones lived four to five months longer than similarly old rats which did not.其他人则利用该技术获得了更惊人的发现。例如，哺乳类动物的骨密度通常随年龄增长而下降。然而，卡姆林的研究过了三年后，老年病学家克莱夫·麦凯(Clive McCay)证明了把老年大鼠和幼年大鼠联体能提升老年大鼠的骨密度。1972年，另一篇论文更令人咋舌地指出，相比同类老年大鼠，分享了幼年大鼠血液的老年大鼠能多生存四至五个月。
The rats themselves, unsurprisingly, were not always keen on the procedure. Early papers describe the dangers of “parabiotic disease”, in which one animal’s immune system rebels against the foreign blood, and also explain how rats must be socialised carefully before being joined, to stop them biting each other to death.当然，大鼠们本身并不太喜欢这个过程。早期就有论文描述过“共生病”的危害——发病时动物的免疫系统排斥外来血液。论文也解释了在把这些试验鼠联体之前，必须先小心地让它们熟络起来，防止互相撕咬致死。
“The technique itself is kind of gross and crude,” admits Michael Conboy, a biologist and parabiosis researcher at the University of California, Berkeley. Perhaps for that reason, research had more or less died out by the late 1970s. These days, though, it is back in the news—for a string of recent discoveries have suggested that previous generations of researchers were on to something. The blood of young animals, it seems, may indeed be able to ameliorate at least some of the effects of ageing. And the technique is promising enough to have spawned human clinical trials.加州大学伯克利分校的生物学家和联体共生研究员迈克尔·康博伊(Michael Conboy)承认，“这种技术本身有些野蛮和倒人胃口。”也许是这个原因，到了20世纪70年代后期，这方面的研究已差不多销声匿迹。不过，最近这种技术又重新回到人们的视线里，因为近期有一连串发现显示，前几代研究人员其实已经摸索到了一些重要的东西。看起来，年轻动物的血液好像确实能够缓解至少一部分的衰老的影响。以该技术的前景，足以催生这方面的人体临床试验。
No jokes about vampires, please
拜托，别拿吸血鬼开玩笑
This modern interest in parabiosis dates back to 2005, when Dr Conboy (who was then at Stanford University), his wife Irina, and a group of other Stanford researchers published a paper in Nature. In it they described joining mice aged between two and three months with members of the same strain that were 19-26 months old. That is roughly equivalent to hooking a 20-year-old human up to a septuagenarian. After five weeks, the Conboys and their colleagues deliberately injured the older mice’s muscles. Usually, old animals heal far less effectively from such injuries than young ones do. But these mice healed almost as well as a set of young control animals. The young blood had a similar effect on liver cells, too, doubling or tripling their proliferation rate in older animals.联体共生的现代研究始自2005年。当时在斯坦福大学工作的康博伊(Conboy)和妻子伊琳娜(Irina)以及斯坦福的其他几位研究人员在《自然》杂志上发表了一篇论文。文章描述了对两至三个月大的小鼠和19至26个月大的同种小鼠所做的联体试验。这大致相当于把20岁的年轻人与七旬老人联体。五周后，康博伊夫妇和同事故意损伤了受试老年鼠的肌肉。通常，老年动物受到这类损伤后的恢复速度远不及年轻动物。但这些老年小鼠的痊愈效果堪比对照组的年轻小鼠。年轻血液对肝细胞也有类似效果，使老年小鼠体内肝细胞的增殖速度提高了一或两倍。
Since then, a torrent of papers have shown matching improvements elsewhere in the body. No one has yet replicated the finding that young blood makes superannuated mice live longer. But it can help repair damaged spinal cords. It can encourage the formation of new neurons in mouse brains. It can help rejuvenate their pancreases. The walls of mouse hearts get thicker as the animals age; young blood can reverse that process as well.自此，有大量论文显示动物体内其他方面也存在类似的改善。但至今尚未有研究重复出年轻血液延长老年鼠寿命这一结果。但研究证明年轻血液有助修复受损的脊髓，还可促进小鼠的大脑形成新神经元，帮助它们的胰腺恢复活力。小鼠的心脏壁会随年龄增长而变厚，年轻的血液还可逆转这一过程。
The effects work backwards, too. Old blood can impair neuron growth in young brains and decrepify youthful muscles. Intriguingly, the phenomenon even seems to operate across species. In April Tony Wyss-Coray, also at Stanford, showed that infusing old mice with blood from the umbilical cords of infant humans improved their performance on memory tests.其中也存在逆向效果。老年血液会损害年轻大脑中的神经元生长，并使年轻的肌肉衰老。有趣的是，这种现象似乎甚至可以跨物种显现。今年4月，同为斯坦福大学研究人员的托尼·魏斯-克雷(Tony Wyss-Coray)表示，老年小鼠输入人类婴儿的脐带血后，在记忆测试中的表现有所提升。
There have been enough results, says Janet Lord, who runs the Institute of Inflammation and Ageing at Birmingham University, in Britain, to remove any doubt that something impressive is happening. But finding out exactly what is trickier. The working theory is that chemical signals in young blood are doing something to stem cells in older animals. Stem cells are special cells kept in reserve as means to repair and regrow damaged tissue. Like every other part of the body, they wear out as an animal ages. But something in the youngsters’ blood seems to restore their ability to proliferate and encourages them to repair damage with the same vigour as those belonging to a younger animal would.英国伯明翰大学炎症和老化研究所(Institute of Inflammation and Ageing)的负责人珍妮特·洛德(Janet Lord)说，现有研究结果足以让人消除怀疑，确信有一些非同一般的因素在起作用。但要确切说明到底是什么就不那么容易了。初步的理论是，年轻血液中的化学信号对年老动物中的干细胞施加了某种影响。干细胞是储备在体内的特殊细胞，用于修复和再生受损组织。就像身体其他各部分一样，干细胞也会随动物的年龄增长而老化。但年轻血液中的某些成分似乎能令干细胞恢复增殖能力，并促进它们像年轻动物的干细胞那样有效地修复受损组织。
Nobody yet knows exactly what that something is, but people are looking hard. In all probability, says Dr Lord, it is not one thing at all, but dozens or hundreds of hormones, signalling proteins and the like, working together. Researchers have been comparing the chemical composition of old and young blood, searching for those chemicals that show the biggest changes in level between the two. These include oxytocin (a hormone better known for its role as a transmitter of signals between neurons); two proteins called GDF-11 and TGF beta-1, both of which are already known to affect cell behaviour; and B2M, another protein which, among other things, affects the body’s ability to absorb iron from food.还没有人确切知道到底是什么在起作用，但人们正在仔细分辨。洛德表示，很有可能不止一种，而是数十或数百种激素、信号蛋白及类似物质在共同作用。研究人员比较了年老及年轻血液的化学成分，寻找两者间含量水平差异最大的化学物质。这其中包括催产素，这种激素更为人熟知的作用是在神经元之间传递信号;还有名为GDF-11和TGF beta-1的两种蛋白质，已知两者均会影响细胞的行为;另外还有一种名为B2M的蛋白质，它的作用之一是影响身体从食物中吸收铁的能力。
Even with a list of targets, working out what is going on is hard, says Richard Lee, a cardiologist at Brigham and Women’s Hospital in Boston, Massachusetts. Blood is complicated stuff, and the tools available to analyse it are far from perfect. Dr Lee’s own work is a good example. In 2014 his group suggested GDF-11 as a possible rejuvenating factor. The following year a team at Novartis, a big pharmaceutical company, said that they were unable to replicate those results. The trouble, said the group from Novartis, was that the test used by Dr Lee’s team was sensitive to proteins besides GDF-11, messing up the results. Dr Lee’s team replied within months that, no, it was in fact the Novartis test that was flawed, because it was itself picking up extra proteins. And there, at the moment, the matter stands.即便有了目标清单，要弄清楚发生作用的过程还是很难，马萨诸塞州波士顿市布列根和妇女医院(Brigham and Women’s Hospital)的心脏病专家理查德·李(Richard Lee)说道。血液是很复杂的东西，现有的分析血液的工具也远非完美。李博士自己的研究便是个好例子。2014年，他的团队发现GDF-11有可能是一种“返老还童”因子。第二年，大型制药公司诺华(Novartis)的一个团队称无法重复该结果。诺华团队表示，问题在于李博士团队的测量方法对GDF-11以外的蛋白质也有敏感性，影响了测量结果。几个月后，李博士的团队予以否认，称有问题的其实是诺华团队的测试，因为正是该团队的测试在过程中混入了其他蛋白质。目前此事件尚无进一步发展。
There are further possible explanations for parabiotic rejuvenation besides blood chemistry. One is that older animals may also benefit from having their blood scrubbed by young kidneys and livers, which mere blood transfusion would not offer. A paper published by the Conboys and their team in 2016, which described blood exchanges that were done in short bursts (thus eliminating the possibility of such scrubbing) reported rejuvenating effects, but ones that were not as widespread as those obtained by full-on parabiosis.除了血液化学方面的因素，联体共生的“返老还童”现象还有其他可能的解释。其一是，老年动物可能也同时受益于年轻肾脏和肝脏对血液的净化作用，而这单靠输血是无法实现的。康博伊及其团队在2016年发表的一篇论文称，在短时间内完成的血液交换(因而消除了上述净化过程的可能性)具有复壮的效果，但不如全面联体共生后那样全面。
Another idea is that cells from the young animal, rather than chemicals in its blood, could be doing some of the work. By modifying the genes of a mouse so that its cells glow under ultraviolet light, researchers can track where those cells end up when the mouse in question is linked to another. They have found that only a few cells from a younger mouse take root in an older animal it is linked to. This does not quite rule the theory out, says Irina Conboy, for the number of cells may not reflect their importance. Immune-system cells, for instance, multiply rapidly when needed. And they are precisely the sorts of cells that might help an older animal.另一个想法是，也许是来自年轻动物的细胞发挥了些许作用，而非血液中的化学物质。研究人员改造了一只小鼠的基因，使其细胞能在紫外线下发光，从而在这只小鼠跟其他小鼠联体时跟踪这些细胞的去向。他们发现，在与老年鼠联体时，只有少数幼鼠的细胞转移到老年鼠体内。但这并不能完全推翻上述理论，伊琳娜·康博伊(Irina Conboy)说，因为细胞数量不一定反映其重要性。举个例子，免疫系统细胞在必要时可迅速繁殖。它们正是那种可能会对老年动物有所帮助的细胞。
The mechanisms by which parabiosis operates, then, are foggy. But that has not dissuaded some companies from setting up trials to see if young blood can work its magic in people as well as rodents. Persuading patients to have themselves stitched to another person so they can share circulatory systems might be tricky. So instead of full-on parabiosis, these trials are using donated blood plasma.如此说来，联体共生的作用机制仍是个谜。但这并没有阻止一些公司展开试验，探究除了啮齿类动物之外，年轻血液是否也会在人类身上发挥神奇的效应。说服患者与他人缝合成一体以共享循环系统可能不大容易。因此，这些试验运用了捐献血浆，而非采取全面的联体共生。
Blood simples
输血蠢行
One such firm, based in California, is called Ambrosia. It has attracted plenty of raised eyebrows for charging its participants, who must be at least 35 years old, $8,000 to join. For that, they get an infusion of blood plasma from a donor under 25. Most clinical trials work by comparing the treatment under investigation either with another, established treatment, or with a placebo. Ambrosia’s trial will not do this. Jesse Karmazin, Ambrosia’s founder, says it would be hard to persuade people to pay if there were a chance they might not get the real thing. Instead, he says, patients will serve as their own controls. This will be done by comparing their blood chemistries before and after the treatment.这类公司中有一家位于美国加州，名为Ambrosia(“长生珍馐”)。该公司要求参与试验者必须年满35岁，并收取8000美元的费用——这一价格令不少人感到惊讶。付钱后，参与者被输入来自25岁以下捐献者的血浆。大部分临床试验要么是将所研究的疗法与另一种已经证实的疗法作对照，要么是与安慰剂组作比较，Ambrosia的试验则不然。其创始人杰西·卡马辛(Jesse Karmazin)表示，如果受试者有可能被分到对照组，那么就很难说服他们付这笔钱来参与试验。他说，患者将充当自己的对照组，通过比较接受治疗前后的血液化学成分来进行临床试验。
The unusual trial design, the charge for participation and the sheer amount of hype surrounding anti-ageing research has led some to accuse Dr Karmazin of being more interested in money than science. Not so, he says. Because blood plasma is a natural product, he says, it is not patentable. Without the prospect of a profitable new drug, no drug companies are interested in sponsoring his work. “If I could run this trial for free, I would,” he says. “But the reality is I can’t.” Indeed, Dr Karmazin would not be drawn on how—or if—he plans to turn an eventual profit. But he argues that, with plenty of blood plasma already being collected, both for transfusion and to extract important biochemicals such as clotting factors from it, checking to see if it might have other useful properties is only sensible. Although Ambrosia is not yet ready to publish its results, its initial findings, he says, are encouraging.由于不寻常的试验设计，加上参与费用和围绕抗衰老研究的大量炒作，已有一些人指责卡马辛意在赚钱甚于科研。他否认了这一点。他说，血浆是一种天然产品，因此不能申请专利。如果没有希望研发出有利可图的新药，制药公司就不会有兴趣赞助他的研究。“我要是能免费做这个试验，我会免费的，”他说道，“但现实是我不能。”的确，卡马辛不愿意透露他是否或者如何计划籍此最终获利。但他认为，已有大量血浆被收集起来，既为输血之用，也为抽取凝血因子等重要生化物质，测试血浆是否有其他有用特性恰是明智的做法。尽管Ambrosia公司还未准备好发表研究成果，但他说初步结果令人鼓舞。
Another firm, called Alkahest, which was spun out of work done at Stanford, has had less trouble attracting money. It began its life in JLABS, a biotechnology “incubator” run by Johnson & Johnson, a big drug firm, and has secured $50m from Grifols, a Spanish company that processes blood plasma into various products. It has commissioned a trial in which 18 people with Alzheimer’s disease will be given four infusions of plasma taken from young donors, over four weeks. The main goal, says Karoly Nickolich, Alkahest’s boss, is to see if the treatment is safe. That should, he says, be fairly straightforward. Blood transfusions are, after all, routine procedures. The study will also, though, check whether the blood used can reverse some of the effects of Alzheimer’s, as seems to happen in mice in analogous circumstances.另一家名为Alkahest(“万能溶剂”)的公司源于斯坦福大学的研究项目，在吸引投资上阻力较小。它最初成形于大型制药公司強生设立的生物科技“孵化器”JLABS，并从生产各类血浆制品的西班牙公司Grifols获得了5000万美元的投资。Alkahest已经委托开展一项试验——在四周内，向18名阿尔茨海默症患者分四次输入年轻献血者的血浆。Alkahest公司的老板卡罗伊·尼克里奇(Karoly Nikolich)表示，试验的主要目标是了解疗法是否安全。他说，结果应该会相当明确，毕竟输血是常规医疗手段。不过，该研究也将检验所用的血液能否逆转阿尔茨海默氏病的某些影响，这对处于类似情况下的小鼠似乎是有效的。
Alkahest plans to present the results of its study at a conference in November. Because the trial is being run by researchers at Stanford, rather than by the firm itself, Mr Nickolich does not yet know what they are likely to show. But if the treatment is safe, he says, and if it proves effective, then the next step will be to identify and isolate the responsible compounds. Unlike blood plasma, such compounds would be patentable—particularly if they were then made synthetically. And such synthesis would be needed. As Mr Nickolich observes, even if things go well, there is simply not enough donated blood around to treat the world’s 44m Alzheimer’s patients with plasma extracts.Alkahest公司计划在11月的一次会议上介绍其研究成果。由于试验是由斯坦福大学的研究人员而非公司自己进行的，尼克里奇还不清楚可能会展示怎样的内容。不过他说，如果疗法是安全的且被证明有效，那么下一步便会是识别及分离发挥效力的化合物。不同于血浆，这类化合物是可以申请专利的，尤其是以后需要人工合成的话。而且也的确需要合成制造。正如尼克里奇认为的那样，即便试验一切顺利，献血量也不足以提取血浆物质来治疗全球4400万名阿尔茨海默症患者。
Some researchers are more wary than Mr Nickolich about the wisdom of such trials. Michael Conboy points out that transfusions are risky. “You can occasionally get immune reactions even with well-matched donors,” he says. “In the worst cases you can get full-on anaphylaxis [an extreme allergic reaction that can be fatal].”对于这类试验是否明智，一些研究人员比尼克里奇更为谨慎。迈克尔·康博伊指出，输血是有风险的。“即便血浆来自配对得当的献血者，也可能出现免疫排斥反应，”他说，“最糟糕的情况是出现全身过敏反应(一种可能致命的极端过敏反应)。”
For his part, Dr Lee worries about the hype that inevitably attaches itself to “anti-ageing” treatments. “I never use terms like ‘anti-ageing’ or ‘rejuvenation’ when I talk about laboratory science,” he says. “It conveys a false sense of hope.” Dr Lord agrees that talk of reversing ageing is premature. But, she says, there are reasons for cautious optimism. Improving the ability of old muscles to repair themselves, for instance, might not be enough to fend off the Reaper for ever. But frailty, and the falls it causes, are a problem for the elderly. Mitigating the damage from Alzheimer’s, even if it cannot be cured, would also be a boon. Rather than lengthening lifespan, says Dr Lord, it is better to think about lengthening “healthspan”. That is not immortality. But it would still be quite something.而李博士则担心对这类试验的大肆宣传难免会使其与“抗衰老”疗法挂钩。“在谈论实验室研究时，我从来不用‘抗衰老’或‘返老还童’这些词，”他说，“这会产生误导，让人空欢喜。”洛德也认同现在谈论逆转衰老还为时尚早。不过她说确有理由持审慎乐观态度。例如，改善老化肌肉的自我修复能力也许不足以长久对抗死神，但年老体衰以及由此导致的跌跤对老年人来说的确是个问题;即便无法治愈阿尔茨海默症，能减轻其损害也是一个福音。洛德说，与其追求延年益寿，还不如考虑怎样延长“健康期”。这不是长生不老，但仍会是件了不得的事。
