This week, playing bingo on an inflatable space station, a new way to attack the cause of Alzheimer's and mending a broken heart with stem cells. Also, using bananas to speed up fruit ripening, leeches out of water and chemical tricks to stop smoking and iron out wrinkles. Plus, in Kitchen Science we vibrate our way to a fountain in a cup!
In this episode
Bouncy Space Station
Las Vegas based space company Bigelow Aerospace have just this week successfully launched their second inflatable spacecraft into Earth orbit.
Bigelow Aerospace intend to launch the worlds first commercial inflatable space station by the year 2010 called Sundancer which will hold a crew of three and in 2012 they intend to launch an add on module called BA330 which will make the whole Bigelow station larger than the current International Space Station.
The recently launched module is called Genesis 2 and is the second test mission using the ultra tough inflatable design. The craft includes 22 cameras, both inside and outside and also contains a number of personal items sent up to space by the public. Mostly people paid to send photos and memorabilia and the first images sent back show these items floating around inside the cabin.
Genesis 2 also carries a bingo ball selector which will be activated in the coming weeks so that people can play space bingo on the Bigelow web page
New Alzheimer's Drug goes on Trial
A new class of drug designed specifically to combat Alzheimer's Disease has entered clinical trials in the US this week. Dubbed CTS-21166, the drug was the brain child of Purdue researcher Professor Arun Ghosh. Unlike existing treatments for Alzheimer's, most of which aim to boost levels of the neurotransmitter acetyl choline, CTS-21166 blocks an enzyme called beta-secretase, which is thought to be responsible for the pathological build-up in the brain of aggregates called beta-amyloid.
These are a neuropathological hallmark of the disease and are thought to provoke the death and dysfunction of nerve cells, which is what triggers the disease. Scientists suspect that if the formation of these amyloid plaques can be prevented then the progression or even the onset of the disease might be delayed. The trial, which is being run by San Francisco-based pharmaceutical company CoMentis Inc., has enrolled 48 healthy volunteers in a phase 1 trial to assess the safety and tolerability of the new drug, with phase 2 trials involving patients with Alzheimer's starting in 2008. Ghosh is optimistic. "The molecule is both highly potent and highly selective, meaning it does not appear to affect other enzymes important to brain function or cause harmful side effects".
Ever wanted to take part in astronomy research, but don't have a telescope? Well now you can get a chance to look through some of the most beautiful astronomical images taken and make a contribution to science in a project called galaxy zoo.
A galaxy is a cluster of billions of stars swirling through our universe. Our sun for example is part of a galaxy called the Milky Way. These galaxies come in a number of varieties. Our Milky way for example is a spiral galaxy, which is flattened like a pancake and has spiral arms containing bright young stars, hence the name a spiral galaxy. But there are other types too large amorphous galaxies with no spirals arms are called elliptical galaxies for example.
A robotic telescope called the Sloan Digital Sky Survey has been automatically taking photos of one million galaxies and these now need categorising. Unfortunately computers have turned out to be incredibly bad at doing this, which is where the Galaxy Zoo project comes in. Members of the public get to be the first human eyes to look at some of these galaxies in return for telling scientists what kind of galaxy you think it is. But don't worry if you think you're not up to the task, full instructions are on the site and initial testing has actually shown that members of the public are better at it than scientists.
So if you're keen then log on to
www.galaxyzoo.org to sign up.
Stem cells get to the heart of angina
Researchers in the US have found that patients with angina who received injections of their own stem cells into the diseased heart muscle showed considerable improvements in their symptoms. Cardiologist Douglas Losordo and his colleagues recruited 24 patients aged 48-84 with severe (grade 3 or 4) angina; on enrollment the patients were symptomatic upon mild exertion; even brushing their teeth was sufficient to provoke chest pain. The team harvested stem cells from the patients by injecting them with a hormone called G-CSF. This encourages bone marrow stem cells to grow and spill over into the bloodstream from which they can easily be collected.
The team used a molecular marker known as CD34 to single out the stem cells, which were then injected into the heart muscle in some of the patients. Others received a placebo. The injections were placed at sites in the heart known as "hibernating myocardium", which are regions of the muscle revealed by scans to contain viable muscle which is largely shut down (asleep) due to poor oxygen and glucose supply. Three to six months after the therapy the patients given stem cell injections had improved significantly. Some of them went from barely being able to make it to the toilet to managing two flights of stairs. The team suspect that the injected stem cells promote the formation of new blood vessels within the muscle, helping to boost the supply of oxygen and therefore increasing the workload that the heart can handle.
"Our goal is to reconstitute the microcirculation, get the blood back into the tissue and alleviate the symptoms," says Losordo.
12:30 - What prevents venomous animals from being killed by their own venom?
What prevents venomous animals from being killed by their own venom?
The reason that snakes, scorpions or other venomous creatures don't poison themselves is because it's kept in a very special compartment in the body, specifically designed not to let the venom out and not to be sensitive to the effect of the venom. In a snake's poison glands, there are specialised cells which have genes activated which tell them how to make the cocktail of proteins (snake venom is a protein) which makes up the venom. The venom is then squirted out into a special system of ducts, lined with cells designed not to be sensitive to the venom. The venom is produced, it trickles down these ducts and into a special bag which holds it and keeps it safely away from the rest of the snake's body until it's needed.
A snake's teeth are hollow and, in the case of the cobra, curved. This means that when the snake wants to bite something, it can lock on to its prey and hook its teeth in. Muscles around the venom bag then contract, squirting the venom out through the hollow teeth and inside the tissue of the victim.
Normal tissue lacks the specialist defences found in the venom producing glands of the snake.
This is very similar to the human stomach. We make digestive juices in the stomach including acid and enzymes which could break down our body's tissues. They are stopped from doing this by the stomach's special lining, which protects it from the effects of the digestive juices.
If you were to inject cobra venom into the normal tissue of a cobra, it would have the same effect at it would on you!
What is the surface of the Sun made of?
The sun itself is made of gas, mostly hydrogen and helium, and so does not have a solid surface like you would find on Earth or Mars. However, if you look at a photo of the sun you can see it has a definite edge to it. This is not because the gas stops at this point, it actually carries on diffusely for thousands of kilometres. The Sun is hotter in the centre and cooler towards the outside, and there is a point where the hot gas becomes cool enough to become transparent, so this point is what we see as the surface of the Sun.
The surface of the Sun is about 5000 degrees Celsius, but inside its millions of degrees. Nuclear fusion reactions occur inside the Sun, much like nuclear bombs going off all the time.
There is also material streaming off the surface of the Sun all the time, which forms the "Solar Wind".
17:05 - Why does tea leave a stain in a cup only in a ring around where the surface of the tea was?
Why does tea leave a stain in a cup only in a ring around where the surface of the tea was?
In hard water areas, the water contains quite a lot of calcium in the form of 'temporary hardness' - calcium hydrogen carbonate Ca(HCO3)2. When this is heated, the temporary hardness breaks down into calcium carbonate, which is chalk, and water. These calcium salts can bind to tannins in the tea and form an insoluble precipitate - a scum. These particles float to the top of the tea, and stick to the side of the cup. Tannins contain some of the colour of the tea, and so this ring of particles will be dark, and stain your cup!
21:31 - Fit Fathers, Unfit Daughters
Fit Fathers, Unfit Daughters
with Loeske Kruuk, University of Edinburgh
The BBC's Autumnwatch programme last year featured the antics of a group of Scottish Red Deer. Loeske Kruuk, from the University of Edinburgh has been studying them, and re-writing some scientific textbooks.
Chris - Loeske, what have you found by looking at these Deer?
Loeske - What we've found is that the genes that make a successful male do not always make a successful female.
Chris - What does that actually mean?
Loeske - Successful fathers, those who sire many offspring, will have daughters who actually have relatively low breeding success.
Chris - Because Darwin would have us believe that as you breed populations you get survival of the fittest, and so everyone should get better as time goes on.
Loeske - Exactly, but what our results are suggesting is that maybe the idea that some genes are better than others, that we can have a single measure of fitness, may just be too simplistic. It may depend on the sex of the individual animal carrying the genes.
Chris - So when you look at a male deer, for instance, what makes a good male would be big muscles, big antlers for fighting... Those genes wouldn't help a female very much, is that what you're saying?
Loeske - Exactly, there are very different traits that contribute to breeding success in males. As you say, fighting ability, antler size and also their skills at roaring, as anyone who watched Autumnwatch will have seen they spend a lot of time [roaring] during the mating season.
Chris - Does this apply to football hooligans as well?
Loeske - [Laughs] It may well do! But those are very different traits from those that determine breeding success in females. With females, those who produce the most number of calves over a lifetime will have the highest fitness, the highest breeding success.
Chris - How did you actually do the study and find these results?
Loeske - Well, we have data from more than 30 years of very intensive study of this population of red deer. And, as anyone who saw Autumnwatch will have seen, we can recognise all the individual deer in the population. It is an entirely wild population.
Chris - Have you named them?
Loeske - We do have names for every animal in the population, yes.
Chris - And your favourite?
Loeske - Well there was Caesar on Autumnwatch as people will have seen.
Chris - That's a kind of dog food, isn't it?
Loeske - [Laughs] Yes and many other attributes as well. There have been some every successful females along the way as well; Aphrodite was one with a very nice name.
Chris - She was very popular with the males, presumably?
Loeske - She did very well...
Chris - So why is it that the males have unfit daughters? Does the same work in the reverse direction? Do you end up with females who are very successful, they have lots of offspring, in the same way as the males' daughters are compromised, are the females' sons compromised?
Loeske - It's slightly more complicated when you look at it that way round, because with females they contribute not only their genes to their offspring's later performance, but they also provide maternal care. So in the Red Deer, all the males contribute to their offspring are their genes, the females provide both genes and maternal care. So a good quality female, although she may be passing on genes which are detrimental in a son, she will also provide very high quality maternal care to both her daughters and her sons. Those two effects seem to balance one another out when you look at the performance of the offspring of the females. It doesn't quite pick up the same relationship in relation to mothers offspring performance.
Chris - So what would you say the bottom line with this study is? That because of the effects you've found, this mechanism contributes to a huge amount of genetic diversity and variation in a population?
Loeske - It's intuitively a very appealing explanation for a lot of the biological diversity that we see in nature. This is important because genetic differences that we see between individuals within a single species have always been quite a puzzling fact for evolutionary biologists, because as you mentioned, the process of natural selection is expected to favour only the best adapted individuals; Darwin's survival of the fittest. What we're suggesting is that maybe the idea of a single 'fittest' genotype is a bit too simplistic.
26:52 - Science Update - Babies!
Science Update - Babies!
with Chelsea Wald and Bob Hirshon
Bob Hirshon - This week for The Naked Scientists we're featuring babies. I'm going to talk about their extraordinary ability to recognize languages, even before they can talk. But first, the sound of a crying baby is said to be one of the most disturbing in the whole world. But Chelsea has found a scientist who can turn it into beautiful music.
Chelsea Wald - [Baby crying] Don't you sometimes wish crying babies sounded more like, say, pianos? [morphs into a piano] Well, you have your wish, at least temporarily, thanks to acoustician Kelly Fitz of the Starkey Hearing Research Center. He says morphing sounds together makes for cool sound effects and innovative music.
Kelly Fitz (Starkey Hearing Research Center) - I always wanted to be a composer, and I thought that this way of working with sound was of interest but the tools just really haven't been strong enough.
Chelsea - His new technique first breaks down two sounds into their component tones, like this. [trumpet sound] Then he adds the components of one sound to the other to make a seamless transformation. [trumpet morphs to crying baby] Oh, so we're back to the baby again? I guess in the real world there's no substitute for just changing the diapers. [To hear the sounds featured in this week's Science Update - Listen to the podcast!]
Bob - Thanks, Chelsea. Babies can barely do anything for themselves, but those as young as four months can tell their native language from a foreign tongue, even if they can't hear a word of either. This according to a study led by psychologists Whitney Weikum and Janet Werker of the University of British Columbia in Canada. Werker says past research has shown that babies can discriminate the sound patterns of different languages from a very early age.
Janet Werker - But because speech is so richly multimodal, and because past research has shown that babies pay attention to both the visual and auditory aspects of speech, we asked "Gee, can they use just the visual information alone, and can they use that to help identify speakers of their native language?"
Bob - Her team showed babies silent videos of bilingual adults, speaking alternatively in English and French. Weikum says that babies' attention instinctively perks up when they detect a language switch.
Whitney Weikum (University of British Columbia) - And we found that at four and six months, babies from the home where only English is spoken can tell the difference between the languages. But their ability to tell the difference between the languages declined by eight months of age.
Bob - On the other hand, babies raised in bilingual homes showed no such decline, suggesting that this ability persists only if it's needed just as the ability to discriminate between certain vowel and consonant sounds fades away, if those differences aren't important in one's native language. As for the ability to distinguish between languages by sight, it's not yet clear whether this is merely a phase of normal language development, or the result of an evolutionary advantage for babies who could recognize other members of their community.
Chelsea - Thanks, Bob. Next time, we'll talk about how scientists are trying to kick the healing process up a notch. Until then, I'm Chelsea Wald...
Bob - ...and I'm Bob Hirshon, for AAAS, The Science Society. Back to you, Naked Scientists...
Why do bannanas ripen other fruit?
The reason it ripens is because bananas happen to produce a huge amount of the ripening chemical that fruit uses, Ethylene. It's the same stuff that can be processed to create polyethylene - plastic. Bananas secrete loads of ethylene, and so it will spread to any other fruit in the fruit bowl. All fruit use ethylene as a signal to ripen, so this is a natural way to encourage fruit to ripen.
If you traumatise a plant, such as by pulling leaves off, it will release a burst of ethylene as a growth signal to the rest of the plant.
33:18 - Want to Quit Smoking and Iron Out Wrinkles? Chemistry can help!
Want to Quit Smoking and Iron Out Wrinkles? Chemistry can help!
with Richard Van Noorden
Chris - Now if you are a smoker and you would like to know how to quit the habit, perhaps help is at hand because joining us from Chemistry World is Richard Van Noorden. Hi Richard.
Richard - Hi Chris!
Chris - You're going to tell us about these chemical strategies that can help people quit?
Richard - Yes. It all seems so simple, if the nicotine is the demon driving tobacco smoking, then you just give the smokers a nicotine-fix and that will keep their hands off the pack. But it's actually 30 years ago since the first nicotine replacement gum was developed in Sweden, and still, according to US centre for disease control, only 5% of those who try to quit smoking succeed in a year.
Chris - With that gum?
Richard - With that gum.
Chris - Which is not much better than will power is it?
Richard - Yes. But fortunately chemists have some new drugs up their sleeve. Number 1 is marketed in the UK as Champix, which received draft approval from the NHS in March, and a decision is being made about it in July, that's this month. It works by cutting the pleasure of smoking and reducing the withdrawal symptoms. It's a bit like nicotine so it binds to the nicotine receptors in the brain and produces dopamine (the pleasure chemical) just like nicotine, but in a slow and long lasting seep, where as nicotine gives you a rush. So, you can use it to alleviate your withdrawal symptoms.
Chris - But don't you get hooked on the Champix then?
Richard - No, as far as I'm aware it's such a small seepage out that it's a bit like the nicotine replacement gum. But the clever thing about this is that although it's a bit like the gum, if you lapse and decide to smoke a cigarette, this drug is already blocking the receptors that nicotine would normally go to, so when you smoke a cigarette you don't get the nicotine rush.
Chris - Didn't this drug originate form the chemicals in a tree in Eastern Europe?
Richard - Yes, the chemical came from the golden rain tree, which has a beautiful name. It has been used since the 1960s by smokers wanting to quit. The chemists changed the structure the molecule slightly, so it's not the same as the molecule you'll find in the tree but like so many chemicals it came from a natural product.
Chris - Like Aspirin. Aspirin came from willow trees. Although the synthetic chemical is very different, the chemical clue was the willow bark. So how do the benefits of Champix compare with Zyban which made the headlines about 10 or 8 years ago, and other things like hypnotism and that kind of stuff?
Richard - Well, they're all actually fairly similar. No one has managed to break the ceiling on 30% long-term quit rate. So all of these drugs that you can take are not very successful so far, but one other strategy you could try is a smoking vaccine, which won't be available yet but I think is incredible.
Chris - How does that work?
Richard - Well, what you do is you take a molecule that looks a bit like nicotine and put a small amount of it in the body and it stimulates antibodies. So when you smoke and nicotine enters your blood stream, the nicotine is swallowed up by the antibodies and forms a big complex. These are too big to cross the blood-brain barrier so the nicotine can't activate the receptors that it normally activates. This is still in clinical trials but it seems promising so far.
Chris - There is a similar technique to treat people who are on cocaine. I think they've done the same chemical trick where you take the cocaine and link it to a molecule that makes the immune system react to it and make antibodies against cocaine. I think it works by blunting the delivery of the drug to the nervous system so you don't get that big chemical surge of pleasure, so you forget to associate taking the drug with feeling good, so it breaks up the addictive cycle.
Richard - Yes. The only problem with vaccine is that the antibody concentration may not be large enough to counter a serious relapse for someone who smokes lots of cigarettes.
Chris - A determent smoker...20 cigarettes in the mouth at once!
Richard - Another problem is that you may not be addicted to just nicotine. When you smoke a cigarette, you are probably also addicted to the irritating rush of smoke against your throat, so just taking nicotine replacement gum doesn't stop you wanting that rush of smoke. Sometimes the best anti-smoking strategy is to smoke a cigarette that doesn't have any nicotine in it, and take nicotine replacement gum at the same time. That way you are actually decoupling the two mechanisms, one the nicotine withdrawal symptoms, that's what the gum is doing, and the other is the pleasure you associate with the smoke and the scent of a cigarette, and that's what the nicotine free cigarette is providing.
Chris - Well, one problem with smoking is that it makes people look a lot older than they really are. There is actually a medical phenomenon called the smokers face and one of things doctors look for in a patient are lines around the mouth and the obvious complexion of someone who has smoked for a long time. But chemistry has a few things that it can throw at the aging process now, I understand.
Richard - Yes. You might remember earlier in May that there were huge queues outside a Boots store when shoppers were keen to get their hands on this anti-wrinkle cream which Manchester researchers had shown that it actually worked. In fact this anti-wrinkle cream contains pro-retinol as an active ingredient, which is not new or exclusive to this product, it's actually the precursor to vitamin A. There are studies to support that in fact vitamin A increases the amount of collagen under the skin. Collagen is a stringy, fibrous protein that makes the skin supple and elastic. But cosmetics are not drugs, a drug with vitamin A in it, for example a treatment for acne, can contain a lot of active ingredients. But a tightly regulated cosmetic can only change the appearance of your wrinkles because they are not allowed to have enough active ingredients to actually do something to your skin.
Chris - So what sorts of chemicals can you put into your skin to iron-out wrinkles.
Richard - Well, we already mentioned vitamin A, you also have vitamin C which is also a cofactor for collagen production, the alpha-hydroxy acids that you get form fruit are acidic and breakdown dead skin cells to leave the new ones underneath, then there is also antioxidants that prevent skin aging by scavenging up the free-radicals. There are also these peptides which are copies of the precursors for producing collagen proteins. So they are all fairly well understood, it's just the case of how much the cosmetic can have in it. Now what's quite interesting is that a new branch called the cosmeceuticals industry is trying to create much more bio-active product, more like drugs and less like cosmetics and they are trying to inject fillers into the skin to stimulate the cells to produce more collagen. This is going to be a huge industry if they ever succeed, but we will see.
Chris - Thank you very much Richard. That's Richard Van Noorden from Chemistry World, at the Royal Society of Chemistry and you can find out more about what he's been up to on the web at chemistryworld.org.
40:44 - The Wellcome Collection
The Wellcome Collection
with Dr Ken Arnold, Wellcome Trust
Ben Valsler: On the 21st of June the Wellcome Collection opened to the public. Sited on Euston road, the Wellcome collection combines three contemporary galleries together with the world famous Wellcome library and a new forum for public debate on science; they offer a fantastic line-up of events throughout the year including music, tours, storytelling and even live surgery.
I spoke to Dr Ken Arnold, the head of public programs for the Wellcome trust, about what to expect.
Ken Arnold: The Wellcome Collection has somewhere near 1500 exhibits, so this is a gallery full of treasures and curiosities. They're arranged in three galleries, one of them is called medicine man where we look at the life and work of Henry Wellcome. Alongside that an exhibition that looks at Medicine Now, so the Human Genome, Malaria, Obesity and the Quest to picture the human body. And then in our temporary exhibition space we've started with The Heart, which looks at both the history of how we've understood the heart, but also not forgetting that the heart is absolutely at the core of our emotional response. So exhibits from around the world that show that sense in which the heart is just as important as a symbol as it is a pump, keeping us alive.
Ben - Visitors will be entranced by the range of unusual artefacts on display in the medicine man gallery. Consisting of hundreds of examples from Henry Wellcome's personal collection, Medicine man offers a glimpse of the history of medicine and of attitudes towards the human body.
Visitor 1: We came here deliberately because we had heard good things about the collection, a bit odd, quite eclectic. Maybe Henry Wellcome was quite a weird chap? And I think I'm probably beginning to agree with that. There are some very, very weird things here, but it's really interesting.
Ben - Certain items in the collection are intrinsically fascinating, as explained by visitor services assistant, Brittany Hudak.
Brittany Hudak: I think that so far people have tended to gravitate towards the Peruvian Mummy, or even people coming in the door have asked "where's the mummy?" Which goes to show that the fascination of the mummified body is apparently still alive and well.
Ken Arnold: This is a mummified male figure in a sort of foetal position with its very delicate skin draped over the skeleton. It's between five and seven hundred years old. One of the things that I'm sure intrigued Wellcome is that fact that actually this is completely naturally preserved. It's simply wrapped in textiles and then dried. It shows that the people who did this had a strong understanding of how to preserve biological material. Also, of course, what we're able to do now is apply modern scientific techniques to study objects like this.
Ben - I spoke to some of the visitors on the opening day to see what aspects of the collection had caught their eye.
Visitor 1: Well at the moment I'm stood in front of a bunch of nipple shields, which is quite interesting, I certainly haven't seen any of those before!
Visitor 2: I think that all the old medical instruments are very interesting and a bit gruesome as well. Dissection models and things like that.
Visitor 3: I found it very interesting to see the changes in different cultures and over time that medicine has progressed, so looking at things like artificial limbs they've had in the past, and how much better ours are nowadays is interesting to see.
Ben - In contrast to medicine man, the medicine now gallery focuses on issues in contemporary medicine. In this exhibition, installations of provocative modern art add an extra dimension to an otherwise clinical display of the tools of modern medicine. I asked Dr Arnold to pick a highlight...
Ken Arnold: This exhibit here is the Human Genome, printed out in all its glory; all 3.4 billion letters of it. We're standing in front of a bookshelf which is almost 5 meters tall, about 2 meters wide and it has 120 volumes, all of them about the size of a telephone directory. To print the Human genome in these books we've had to reduce it to 4.5 point type, so type that's about a quarter of the size of the average newspaper type. You open a volume and you find just millions and millions of C's, of T's of G's of A's. And as a source of information this at once seems like the most extraordinary book of life, both literal and metaphorical, and yet in a curious way it also means nothing to the average person on the street. There is then this kind of tension here of being the richest source of information we could possibly have, and yet also maybe at the same time the deepest mystery.
Ben - In addition to the two permanent galleries, The Heart exhibition is the first to fill the temporary gallery. Exploring both the anatomical function of the heart as well as its powerful cultural symbolism, this exhibition includes ancient Egyptian artefacts and Leonardo Da Vinci drawings through to cutting edge cardiovascular imaging technology, even detouring through the music of Hank Williams.
Ken Arnold: This is the most recently added exhibit to the heart show. It is a Human heart. It doesn't look too healthy; it's got lots of yellow tissue on the outside of it. Remarkably enough, this heart was beating inside the chest of Jennifer Sutton just a fortnight ago. She had a heart transplant operation and was good enough to allow us to put it on display. So we have the remarkable possibility that Jennifer could, when she's feeling a bit better, come in and actually look at her own old heart.
Ben - By marrying science with art, historical with contemporary, the Wellcome Collection provides something to engage everyone.
Brittany Hudak: I rather enjoyed today watching people kind of looking at an object and then going and opening one of the cabinets and learning about it and going "Oh My Gosh! Do you know what that is?" I do feel like light bulbs are going off all over. It really is an individual experience, I think everyone in here could find something different that they would enjoy.
Ben - For more information about how to find the Wellcome Collection, its opening hours and details about upcoming events, you can visit the collection's website, at
What are flames made of?
Flames are simply soot particles made when a wick (in the example of a candle) burns. Because these soot particles are so hot, travel upwards and glow, just as a red hot poker might glow. They glow a yellow colour and so create a flame.
What shoud I do with leeches in my pond?
Leeches are a member of the worm family, and do not have to live in water, as long as they don't risk drying out. It's unlikely that they will harm you; in fact medically speaking leeches have been used for centuries.
The saliva of leeches contains a natural anti-coagulant called hirudin. This stops blood from clotting. If a surgeon needs to reattach a body part, it's relatively easy to attach the arteries that supply blood, but much harder to attach all the tiny veins which allow blood to get back out. When lots of blood goes in and can't get out this creates blood clots which can cause tissue to die. If you attach leeches, they suck out some of the blood, establishing blood flow and avoiding clots.