3. Locked up in a cell
You have no doubt cut yourself at some point and seen deep red blood well up from the wound. If you have a sterilised needle handy and would like to prick the ball of your thumb to take a closer look at a drop, feel free (provided you have no medical problems that make this dangerous) – but it’s not essential. If you do decide to give this a go, as you stick the needle in, you may feel the urge to swear. And this isn’t necessarily a bad thing.
Cursing the pain away
Research carried out in 2009 suggested that there is a good reason that we tend to yell expletives when we hurt ourselves. By comparing the effects of swearing against using everyday words, it was discovered that yelling swear words increased the ability to tolerate pain and decreased the amount of pain that was felt. According to the research, this relief didn’t apply to men with a tendency to ‘catastrophise’. As this word isn’t in the Oxford English Dictionary, I’m not entirely sure what the scientists mean by it – I can only assume it’s a tendency to be a drama queen.
The suggestion from the research was that swearing could break the link between fear of pain and the feeling of pain, reducing self-induced suffering. Whether this helps or not, there is a small amount of suffering required if you want to take a look at that drop of your blood.
A living liquid
Here is something very different from that lifeless hair. There is no doubt that your blood is active in a way your hair isn’t. Yet it isn’t easy to say at what point we move from something that is dead to something that’s alive. Down at the level of atoms, the blood is no different from your hair, or, for that matter, from a rock. The specific mix of atoms may be different – there’s a significant amount of iron in the blood, for example – but both are still made up of assemblies of atoms in the form of various molecules. Yet somehow the ‘living’ blood and the dead hair are different.
Deciding for certain whether or not something is alive is a surprisingly non-trivial task. Before you read on, see if you can list at least six things that distinguish something that is living from something that isn’t.
At one time it was thought that there was a ‘life force’, a form of energy that was present in living things, but that wasn’t there when they were dead. But this energy has never been detected and the life force is no longer taken seriously outside of pseudoscience and metaphor (‘she looks full of energy today’).
The signs of life
Instead, biologists look for seven signs that life is underway, known as life processes. Life is, in effect, defined by what it does rather than what it is. These seven processes are:
- Moving – even plants move over time; watch a sunflower follow the Sun
- Nutrition – consuming something to generate energy, whether that something is plants, animals or sunlight
- Respiration – the process by which energy is produced from the ‘food’ source, often but not always involving oxygen
- Excretion – getting rid of waste matter
- Reproduction – making new copies of themselves (often with variation) to continue the species
- Sensing – having some interaction with what is around, usually by detecting forms of energy
- Growth – though not a constant throughout life, all living things grow at some point in their development.
At the level of an organism – a plant or animal – the simple rule is that unless all these processes take place, whatever you are looking at isn’t alive. Get all seven and you probably have a winner. Even here, though, making the ‘dead or alive’ call is not always totally clear. Take the virus that gave you an irritating sniffle some while back. You could regard a virus as a single-celled living thing. There are plenty of things that only have a single cell that definitely are alive, bacteria for example. Yet viruses fail on the reproduction test.
It’s not that viruses don’t reproduce – it is their reproduction that causes problems in your body. But the way they do it is to commandeer the mechanisms of their host’s cells. In a sense, when you get a virus, it’s your life that reproduces a virus, not its own. Many – though not all – biologists do not consider viruses to be alive, and in part it’s the lack of life that makes it particularly difficult to get rid of them. You certainly won’t get anywhere with an antibiotic, which is why taking these for colds and flu is a waste of time.
Are your cells alive?
It’s harder still to be sure if something is alive when looking at a part of a living thing. With the exception of single-celled creatures, an organ or a cell taken in isolation certainly won’t fulfil all the criteria – your heart can’t reproduce, for example.
Life, as the biologists use the word, is a holistic term that really only works at the level of an organism. When an animal goes from being alive to being dead, we can’t see immediate changes in every cell, though eventually they will come. So with this interpretation we can’t say that a drop of your blood or a cell from your finger is alive. And yet there is so much more going on in there than was the case with your hair. We can’t say that flesh and blood is dead in the same way as hair – parts of a living thing, like blood or a cell from the flesh of your thumb, will typically exhibit some (but not all) of the life processes.
I asked a cell biologist if she thought cells are alive, and she was very certain that they are. As she pointed out, ‘This is never more evident than when you’ve had a bad day in the lab and you end up killing your cell cultures by mistake. Cells that are alive metabolise, and divide, and move around – if you film them with time-lapse microscopy, they are amazingly dynamic, quivering and pulsating and sending out probing little fingers (filopodia) and feet (lamellipodia); some cells even crawl around. And of course, they reproduce themselves, some endlessly, like immortal cancer cell lines. When cells die, they retract all their fingers and feet, and round up – their nucleus disintegrates and they sort of explode. Then they are utterly motionless, never to rise again. So in my view, this is clearly the difference between life and death!’
Blood cells are tricky in this respect. Unlike most of your cells they don’t have a nucleus (more on this soon) and they just go with the flow with the circulation of your blood. However, they still play a hugely important and active role in keeping the rest of you alive.
A voyage through your bloodstream
If you look at a drop of blood that oozes from a pinprick on the end of your finger, it seems to be a dark red liquid with no particular bits and pieces in it – but get a smear of it on a microscope slide and it is packed with small objects. Some, the red cells, are like little lozenges, resembling tiny dried apricots. Their role is to carry oxygen from the lungs to the body tissues.
These cells are red because their main constituent is a protein called haemoglobin (your many different proteins are amongst the most important worker molecules in your body). Take away the water from red blood cells and 95 per cent of what’s left is haemoglobin. This large molecule is excellent at binding onto oxygen to carry it around the body. Haemoglobin contains iron, and it is often thought that this causes the red colour just as it produces the red tint of rust, but the colouring is a coincidence. The iron atoms are bound in a ring of atoms called porphyrin, and it is this organic structure that provides the colouration. The red blood cells are produced in your bone marrow and typically whizz around your body every twenty seconds for around four months, along with trillions of others, before they are replaced.
The other familiar occupants of that drop of blood are the white blood cells. There are many types of these, acting as defence mechanisms and clean-up operatives. One kind of white blood cell disposes of old red cells when they are past their prime. But most are on the hunt for sources of disease and other unwanted substances that may have got into the body.
Although you can’t make out individual white blood cells with the naked eye, you’ve probably seen a collection of one kind of white blood cell that have done their job and died – they make up pus. There is a whole army of these cells in your body, billions of them, each dedicated to taking on particular forms of attacker or internal cells that are in need of culling.
That’s not the end of blood’s armoury. There is also a third type of cell in the blood that may be less familiar – platelets. These are short-lived, rather shapeless cells that are responsible for blood clotting, preventing wounds from bleeding indefinitely.
The special molecule
Of course there’s another component of blood as well – water. The plasma (we are not talking about states of matter now, remember) that the blood cells float in has a number of proteins and other chemicals dissolved in it, but it’s primarily water. Your body contains lots of water – more water, in fact, than anything else. Water is a simple but fascinating molecule. One oxygen plus two hydrogens makes that most familiar of chemical formulae, H2O. Water has huge significance for biology, so much so that when we search the Solar System for likely sites for life, we first look for water. Bacterial life has been found at the extremes of heat, cold and airlessness that our planet can serve up. But there is no known life without water.
Underlying water’s importance is a unique collection of properties. It’s the only compound that exists as solid, liquid and gas at the typical temperatures we experience on the Earth’s surface. And as a molecule it has some surprising characteristics – without one of these, its boiling point would be below –70 degrees Celsius. If that were the case there would be no liquid water on Earth, and so no life. But thanks to this special property the water molecule shares with a few others, it boils at the familiar 100 degrees Celsius.
The property in question is hydrogen bonding, an attraction between the electrical charge on a hydrogen atom and that on another atom like oxygen, nitrogen or fluorine. In the case of water, the hydrogen’s relative positive charge is attracted to the slight negative charge on the oxygen in another water molecule. The result of this bonding is that it’s harder to separate the molecules into a gas than it otherwise would be. The bond has to be overcome, pushing up water’s boiling point and so making the Earth habitable.
Hydrogen bonding is also responsible for another of water’s unusual properties. Most substances occupy less volume as a solid than they do as liquid. However, solid water – ice as we tend to call it – has a higher volume than the liquid form, which is why it’s not recommended to freeze a bottle full of water, and why ice floats on a pond, making it easier for life to survive under it. It’s often said that this is a unique property of water. It’s not – acetic acid and silicon, for example, are both less dense as a solid than as a liquid – but it is unusual.
Fill a small plastic bottle with water right up to the top, leaving no air, and screw the top on. Leave it in a freezer overnight. As the water expands to form ice it will either crack the plastic, force the top off or stretch the plastic so it feels strangely floppy once it has thawed. Don’t use a glass bottle or you may get shattered glass all over your freezer.
The reason for this expansion on freezing is that the shape of the standard crystal form of water, a six-sided lattice, won’t fit with the way the hydrogen bonds pull the hydrogen of one water molecule towards the oxygen of another. To slot into the structure, these bonds have to stretch and twist, pulling the water molecules further apart than they are at water’s most dense form (which is at around 4 degrees Celsius).
Water is, of course, transparent but it does have a slight blue coloration due to the scattering of light (the same reason the sky is blue), although this is not obvious except when there’s a large amount of water we can see through, for example in glacier ice.
One of the reasons water is so important for life is that it is a great solvent thanks to the charges on the molecule than make hydrogen bonding possible, dissolving many other materials and acting as a transport for them in living cells. But this isn’t the only way that water supports life. It takes part in many of the chemical reactions necessary for the metabolic processes of the body. Without water, living cells can’t exist.
A company of tiny boxes
I’ve already used the term ‘cell’ repeatedly. You can’t avoid it once you start to take a look inside your body. The word was coined by Newton’s contemporary (and arch rival) Robert Hooke. A great scientist in his own right, Hooke’s best-known book is Micrographia, a wonderfully illustrated study of the very small, seen through magnifying glasses and early microscropes.
The illustration of a flea in Robert Hooke’s Micrographia
Some of the illustrations folded out of the book, stunning the readers of the day with detailed images of a flea and a louse, two creatures with which they would be all too familiar, but which they would never have seen in such monstrous detail. He also amazed his public with a detailed drawing of the compound eyes of a fly. He even studied sections of cork. In these he saw an ‘infinite company of tiny boxes’ which he likened to the cells occupied by monks in a monastery. The biological cell is named after a monk’s bedroom.
Every known living thing has at least one cell. The simplest forms of life – bacteria, for example – consist of a single cell, while your body has trillions of them. In effect each cell is a container of life. The blood cells we’ve already met are fairly unusual, but the more standard forms in your body are complex packages with a central nucleus and various bits of biological machinery floating around in the fluid surrounding it.
The superstar molecule
That nucleus houses the most famous complex chemical compound in existence, DNA. Let’s face it, DNA is a celebrity of the chemical world. How many other molecules regularly get mentioned on the news? We don’t even have to give its full name – the initials are enough. (Which is just as well as deoxyribonucleic acid doesn’t trip off the tongue.) And we only have to see a picture of a double helix to know what we’re dealing with.
DNA is not a single substance. It’s not like salt, say, which is always sodium chloride, a simple compound of two atoms stuck together in the NaCl molecule. DNA is more of a format for storing information in chemical form. The DNA in the nucleus of one of your cells – let’s say a cell in the flesh of your fingertip where that blood oozed from – is in the form of a series of long molecules, twisted around proteins called histones that act rather like a set of spindles for the DNA.
You may have seen pictures of human chromosomes. Each chromosome is a single molecule of DNA with its accompanying histones, and each of your cells contains 46 of these chromosomes in the nucleus. We’ll find out more about these in Chapter 7, but the important thing that often isn’t mentioned when people are talking about chromosomes is that the DNA in each one is a single molecule. This isn’t obvious because they are wrapped up in a bundle, making them much more chunky than a typical molecule. Their sheer size is also part of what distracts us from thinking of them as a molecule. The DNA in human chromosome 1 is the largest molecule known, with around 10 billion atoms in it.
Experiment – DNA dabbling
Here’s a chance to experience what those forensic science dramas on TV are up to when they isolate a DNA sample. In this experiment you can extract DNA from a banana. It is the most complex experiment in the book, but even if you don’t do it, it’s still impressive that you can get hold of DNA with a relatively simple bit of science.
Blend half a banana to a paste (just blend for a few seconds – don’t let it become too liquid). Mix clear liquid dishwasher detergent and a pinch of salt with around nine times as much warm water to fill half a mug (say 10cc of detergent, making up 100cc of solution). Stir this and the banana together, trying to avoid creating bubbles, until you have an even mix with no lumpy bits.
Use a coffee filter to filter the liquid from this mix in a cold place. Put some of the liquid in a narrow glass container (a test tube would be ideal) so it’s a couple of centimetres deep. Now gently pour very cold alcohol down the side of the container so it forms a layer on top. DNA will begin to come out of solution in the alcohol. You should be able to spool it out on a cocktail stick.
Ideally the alcohol should be 95 per cent ethanol – effectively pure alcohol. If you can’t get hold of this, rubbing alcohol should work. Alcoholic drinks are not pure enough. You don’t have to use a banana – practically anything living will do, but bananas are one of the easiest things to use. Note that the final gunk will have some proteins attached, but it’s mostly DNA.
That double helix structure of DNA is very similar to a spiral staircase. The helix part consists of long strings of sugars – the ‘deoxyribo’ in the full name of DNA comes from the sugar deoxyribose that forms part of these backbone polymers, long chains of atoms with a repeating structure. As far as DNA is concerned, these are just foundations. The important constituents are the treads of the spiral staircase. Each tread is made up of a pair of chemical compounds, which are selected from the four ‘bases’: cytosine, guanine, adenine and thymine.
Your own special code
These bases are like the zeroes and ones in binary code in a computer (though of course bases are not binary because there are four of them). There are six billion base pairs in the DNA that is found in each of your cells. The codes there are used to store information that will be used to produce various proteins, the multi-purpose workers of the biological world, and to create a whole set of other molecules that help determine how you are formed and develop over time. What makes the whole thing work is that the treads always have the same coupling of bases. Adenine is always paired with thymine, while cytosine is always linked to guanine.
This pairing is the key to a copying mechanism. New cells are produced by splitting one cell into two, and each of the resultant cells needs its own copy of the DNA data. To do this, the two chains of the double helix are unwound, dividing each of the treads in two. Although those two halves are not identical, because the base pairs always couple up the same way, it’s easy to recreate the missing half and end up with a complete set of DNA in each cell.
DNA is often described as providing the blueprint for the living thing that contains it – and it certainly has quite a job to do. Just think of it. You started off as a single cell. That cell divided into two, the two cells divided into four and so on until you reached your current, magnificent, total of about 50 to 70 trillion cells. Clearly things couldn’t just continue that way with simple splitting or you would just be a big blob of cells. Something had to give directions for the cells to know how to ‘differentiate’ – to form different types of cells and different structures – and that’s the role of DNA.
However, to call DNA a blueprint is misleading. A blueprint gives you detailed specifications of exactly what goes where so you can build an artefact. But DNA has nowhere near enough data in it to specify everything that goes into a human being. There is certainly no link between the number of genes – the basic code level of the information in the DNA – a living thing possesses and its complexity. Rice, for example, has more than twice as many genes as human beings do. However, this is a simplistic view, as we’ll see when we examine genes in a bit more detail.
Instead, then, it’s better to think of the DNA in your fingertip (and every other normal cell in your body) as the control software of the complex automated factory that is a living thing. The DNA doesn’t contain all the details, and other factors are interacting with the software, changing which parts of it are active at any one time. Nonetheless, as we’ll see in more detail in Chapter 7, DNA has a hugely important part to play.
The 46 molecules of DNA in the nucleus of a cell aren’t the only DNA in that cell, though. In fact there’s some extra DNA that you could think of as alien – it doesn’t originate in a human being at all.
The invaders in your cells
Floating around in a cell but outside the nucleus you will find structures called mitochondria. These minuscule pods are sometimes called the cell’s power plants, as their job is to take the oxygen collected by breathing (delivered by the red blood cells) and combine it with chemicals from your food to make ATP, adenosine triphosphate, a molecule that your body uses to store up energy. The mitrochondria are biochemical battery chargers. The most remarkable thing about them is that they appear to have once been bacteria that became part of the cell in a mutually beneficial symbiosis.
This theory for the origin of mitochondria has been around a while, but the evidence for it became even stronger in 2011, when a common marine bacterium with the rather boring name SAR11 was discovered to be likely to share a common ancestor with our mitochondria. It’s a bit like humans and gorillas – we both share a common ancestor and so, it seems, do SAR11s and mitochondria. Comparison of the genes in the two suggests that they originated in the same early form of bacterium.
This comparison was possible because mitochondria have their own DNA – just thirteen genes that are separate from your main chromosomes in the nucleus of the cell. Unlike your principle body of DNA, which is a mix-and-match combination from both your parents, the mitochondrial DNA only comes from your mother. These built-in ex-bacteria need the action of around 1,000 genes to work. In the distant past all those genes would have been on board the single cell that became a mitochondrion, but over time all but the thirteen have migrated out to the chromosomes.
The number of mitochondria present varies from cell type to cell type. They are at their most dense in your liver cells, where you will typically have over 1,000 mitochondria in each cell. Although mitochondria have a number of other functions, their biggest role is storing energy away in ATP, which is the chemical equivalent of a coiled spring in a clockwork motor.
When a spring is wound up, it takes energy to twist it into a tight form. That energy is stored until the spring is released, when it can push on a mechanism and make it go. Similarly, the mitochondria store energy by creating ATP. This rather messy chemical (its full name is dihydroxyoxolan-2-yl methyl (hydroxyphosphonooxyphosphoryl) hydrogen phosphate) contains a pair of bonds that link phosphorus atoms with a single oxygen atom. These bonds (linkages between the electrons in the atoms) are relatively weak, and a simple chemical reaction will result in the bonds breaking, giving off energy in the process. It is the combination of tiny doses of energy from these molecules that gets your muscles moving every time you lift a finger or carry out any other action. Just to keep your eyes following this text, ATP bonds are popping all over the place.
Wearing your alien genes
Mitochondria aren’t the only invaders that have been completely integrated into your body. Your DNA includes the genes from at least eight retroviruses. These are a kind of virus that makes use of the cell’s mechanisms for coding DNA to take over a cell. (Aids is produced by such a virus.) These viral genes in your DNA now perform important functions in reproduction, yet they are entirely alien to human DNA.
If mitochondria were once bacteria, they are now very much part of your cells. Although they don’t turn up in the more basic single-celled creatures, they are present in almost all organisms that have a nucleus in their cells. It seems the mitochondrial invasion took place at a very early stage of the development of more complex life on Earth. However, they aren’t the only bacterial presence in your body.
Your trillions of tiny stowaways
Next time you take a look in the mirror, remember this. On sheer count of cells, there is more bacterial life inside you than there is human life. There are almost ten trillion of your own cells in that body – but as many as ten times more bacteria than that.
Many of the bacteria that call you ‘home’ are friendly, in the sense that they don’t do any harm. Some are positively beneficial. They aren’t as integrated into your system as mitochondria, so it is possible to live without them, but losing them makes life harder. Back in the late 1920s an American engineer decided to investigate whether animals could live without any bacteria whatsoever, hoping that a bacteria-free world would be a healthy one. James ‘Art’ Reyniers made it his lifes work to produce environments where guinea pigs and other animals could be raised bacteria-free from birth.
The result was clear: it was possible. You could clean away all those nasty bacteria and it wouldn’t stop animals from living. As a bacteria-free world would clearly reduce the potential for disease, Reyniers’ results encouraged the widespread use of antibacterial cleansers and antibiotics.
There is no doubt that some bacteria cause a huge amount of harm. It turns out, though, that Reyniers’ research was misleading. He did indeed get some of his guinea pigs to live without bacteria. But many died. And those that did live had to be fed on special food. This is because bacteria in the gut help with digestion. This is particularly important for animals and insects eating plants high in cellulose, like grasses and wood. These foods are difficult to break down, and without bacteria to help, animals with this kind of diet wouldn’t survive.
You could live without your bacteria – but without the help of the enzymes in your gut that bacteria produce, you would need to eat food much more loaded with nutrients than your usual diet. This is particularly true for vegetarians, as plant fibres are particularly resistant to our own enzymes and it’s only with the help of the much wider range of chemicals produced by bacteria that we can get anywhere with them.
This is something you need to bear in mind if you take a course of antibiotics. Although any particular antibiotic will only kill a percentage of bacteria, there is no distinguishing between ‘good’ bacteria and ‘bad’ bacteria. Antibiotics don’t care. They will, without doubt, cut a swathe through the bacteria in your gut. This means that you may need a richer diet for a while, and will also have to be careful to avoid infection – the bacteria in your gut help fend off unwanted intruders, so if you knock out these locals with antibiotics it is significantly easier for a new and possibly harmful strain to take hold.
Sadly for those who enjoy them, there is no evidence that adding ‘friendly bacteria’ in the form of pro-biotic drinks and other products has any positive effect. The bacteria consumed this way will make very little contribution to your in-house fauna. There is probably some psychological benefit (see page 267 on the placebo effect), but no genuine biological assistance from those friendly bacteria.
A useful appendix
Bacteria are also part of the story in what is probably the most misunderstood part of your body: your appendix. If you still have your appendix, you might wonder what the point of it is. After all, the appendix sometimes goes wrong and causes potentially life-threatening appendicitis, yet it doesn’t seem to do anything useful. This surely does not make evolutionary sense. Given that human beings have had appendixes for a long time, if they are totally useless, why haven’t they disappeared entirely?
It is only relatively recently that it has been discovered that the appendix is very useful to your onboard bacteria. They use it as a kind of holiday home; somewhere to get a respite from the strain of the frenzied activity of the gut; somewhere to breed and help keep the gut’s bacterial inhabitants topped up. So the appendix isn’t as useless as it has traditionally been regarded.
But it seems strange that the bacteria inside you, even those in the appendix, aren’t mopped up by your defensive systems. White blood cells are constantly producing antibodies, proteins designed to lock onto invaders and cripple them. This is why transplant surgery is so difficult – human bodies even tend to fight off other perfectly harmless human cells. Yet by mechanisms we don’t entirely understand, all these bacteria seem to be able to resist the actions of the antibodies.
One other surprise about the appendix is the recent discovery that it contains vast quantities of antibodies. Some of these do have a way of latching onto some of the bacteria that find their way to your gut, but in a helpful, rather than destructive way. The most common antibody in the gut, also very common in the appendix, is called IgA. This binds onto the gut bacteria – but not to kill them. Instead, it forms a supportive structure that helps the bacteria stick in place and thrive in the gut, rather than being flushed out as if they were food. Your antibodies give a helping hand to these useful gut bacteria.
The name IgA is short for immunoglobulin A. There are huge numbers of such proteins, large complex molecules produced in the body and used as chemical workhorses. Initially these were given sober and serious names like immunoglobulin, but over time a tradition has developed of landing them with quirky ones. So we have proteins called sonic hedgehog, pokemon, seahorse seashell party, dickkopf, R2D2, Homer Simpson, glass-bottomed boat and, my favourite, abstinence by mutual consent.
Bacteria don’t know the five-second rule
Bacteria (and viruses) aren’t, of course, always good for you. Although some illnesses are genetic or due to normal human processes going wrong, most are probably caused by one of these types of tiny invader. An old wives’ tale that we need to check against our knowledge of bacteria is the five-second rule – the idea that if you drop a piece of food, as long as you pick it up within five seconds you should be okay.
Apparently this approach dates all the way back to the time of Ghengis Khan, though back then, when people were less fussy about what they ate, it was the twelve-hour rule. A US high school student, on a summer course at a local university, took a more modern scientific approach to the rule, with some interesting conclusions.
When Jillian Clarke took swabs from floors at the university, including areas with a high footfall, she discovered that the floors were surprisingly clear of bacteria. The PhD students helping her couldn’t even find countable numbers of them. However, perhaps not surprisingly, they did discover that people are less likely to pick up from the floor and eat broccoli or cauliflower than sweets or biscuits.
Perhaps the most important finding was that when a surface was inoculated with E. coli bacteria, foodstuffs did pick up the bacteria in under five seconds – so in that sense the rule fails.
Worming their way into your affection
Bacteria may be the most common alien life form that you will have on and in your body, but they certainly aren’t the only ones. Some people will have undesirable guests. Lice, for example (see page 17), or fleas, not to mention worms. Worms are fascinating – we tend to think of them purely as unwanted parasites, but there is now some evidence that the right worms in the right circumstances can be beneficial.
This may seem a bizarre suggestion, but though they are a more recent companion than the bacteria we depend on, human beings have lived with worms for sufficiently long that our bodies have grown used to them. Although trials are still relatively infrequent (quite possibly because of the revulsion worms cause), there is reasonably good evidence that some worms can have a beneficial effect on the body, because our internal systems expect them to be present and are out of kilter without them. It has been suggested that some medical conditions that have increased in frequency as worms have been wiped out could be improved with judicious application of worm therapy.
The noble leech
Another parasite that has a positive side is the leech. Leeches have been used medicinally for hundreds of years, but the traditional use was based on a totally false premise. Medicine has only recently become scientific. For a long time it hung onto an idea that was the medical equivalent of the Ancient Greek four elements, that of the four ‘humours’. This was based on the belief that the body contained four liquids that maintained its equilibrium: blood, phlegm, black bile and yellow bile.
These humours had to be kept in balance. If you were thought to have too much blood, for example (and so were ‘sanguine’), some would be removed by bleeding. This bloodletting was a common treatment, and often made patients significantly weaker and less able to fight off infection than they would otherwise have been. While it was frequently performed directly by incision, leeches were sometimes used as a convenient way to remove blood.
Although, thankfully, modern medicine has realised the ineffectiveness of bloodletting, leeches have come back on the scene to help with some post-operative problems. A blood-sucking creature like a leech wants blood to flow smoothly without clotting. To help this, it applies a natural anticoagulant as it sucks. An operation can sometimes result in congestion where blood builds up in some regions and doesn’t reach others. Careful use of leeches can clear the congestion and help the blood to flow better into the tissues that are not receiving a good supply.
Aliens in the eyelashes
Depending on how old you are, it’s also pretty likely that you have some other aliens on board. There are tiny creatures called eyelash mites that live on old skin cells and the natural oil (sebum) that is produced by human hair follicles. Unlike lice, these mites are only surface feeders and don’t do any damage, though they can cause an allergic reaction in a minority of people. They are very small – typically around 1/3 of a millimetre when fully grown and near-transparent – so you are very unlikely to see them with the naked eye.
Put an eyelash hair or eyebrow hair under the microscope, though, and you may well find these little creatures, which spend most of their time right at the base of the hair where it meets the skin. Around half the population have them, with children having fewer and older people more. Although they don’t have the positive benefits of bacteria, there is no need to worry about eyelash mites – they are harmless.
Seeing small
Such miniature invaders have only really become part of our conscious understanding of the body with the use of microscopes. Similarly, cells only began to be understood as this technology became more widely available. The first observations, like many of Hooke’s, were done with a strong single lens, supported to avoid vibration. This was also true of the man who discovered bacteria in 1674, Anton von Leeuwenhoek. But real advances depended on the introduction of the compound microscope.
By simply putting two of the right lenses together in a tube, our ability to delve into the nature of microscopic life was much enhanced. A lens close to the object being studied produces a magnified image on the opposite side of the lens. This is a ‘virtual’ image – you can’t see it, it floats in space. The second lens, the eyepiece, then acts as a magnifying glass focused on this already enlarged image.
We can thank a Dutch father-and-son team, Hans and Zacharias Janssen, for this invention. These Dutch spectacle makers put together their first compound microscope around 1590. At the time Hans was only a boy. He tends to be the better known of the two because his future career was based on optical instruments, but it’s arguable that Zacharias should have most of the glory.
Our current knowledge of the working of the body has been enhanced greatly by other technologies that enable us to see beyond the immediately obvious. The first real breakthrough was the use of autopsies to explore the inner workings of the body, a process that was hampered because for many years it was illegal to undertake such operations. But cutting a person apart to see what’s going on inside has its limitations, particularly if they are alive, and modern technology has a number of other answers to this need.
The rays that don’t stop giving
The first big breakthrough was back in 1895, an accidental discovery when German scientist Wilhelm Röntgen was experimenting with a ‘Crookes tube’. This was a crude form of the cathode-ray tube which was used in TV sets and computer monitors until LCDs and plasma took over. The ‘cathode rays’ of this tube are actually a stream of electrons, which can be steered using electrical and magnetic fields. The electrons usually end up hitting a phosphorescent screen which lights up where they arrive.
These glowing screens were built into the front of TV sets, but Röntgen had a free-standing screen, which he had left to the side of the tube rather than placing it at the target end. He was amazed to discover that it still glowed when he switched the tube on, despite the sides of his tube being swathed in cardboard to stop stray emissions. It seemed that the electrons, hitting a metal target, were generating some new kind of ray that shot off sideways and was so powerful that it went straight through the cardboard.
Röntgen referred to this new form of radiation as X-Strahlen (pronounced Eeks-Shtrahlen), which in English became X-rays. The ‘X’ just meant this was something unknown and mysterious, and the term was only intended as a temporary nickname. The scientific establishment didn’t like it and tried to call the effect Röntgen rays, but it was too late, the term ‘X-ray’ stuck.
Back then, just as now, a scientific paper sometimes caught the attention of the press, and Röntgen’s paper on the discovery of X-rays had one feature that made the headlines: a single photograph. Röntgen had shone the X-rays onto his wife’s hand. They passed through flesh, but not through bone. For the first time ever, the photograph showed a human skeleton inside the flesh; a picture of his wife’s bones. It was even more striking as his wife had not taken off her wedding ring (although she seems to have tried to, as it’s above the knuckle), so this stands out as a dramatic blob on the image.
The medical applications of this were so stunningly obvious that the world’s first X-ray unit was set up at Glasgow Royal Infirmary in 1896, just one year after their discovery. The users of medical X-rays have never looked back. What’s more, the general public could not get enough of the novelty of X-ray vision. Well into the twentieth century amateur electrical magazines featured DIY designs to build your own X-ray machine, and as a child my shoes were still being checked with a device that let you look down and see your own toe bones inside the shoe.
What was not realised initially was that, marvellous though X-rays are, they come with risks attached. Röntgen suspected from the beginning that they were a form of light, which they proved to be. X-rays are exactly the same stuff as visible light, but with higher energy. We know that electrons can be bumped up to a higher level by absorbing a photon, a quantum of light energy. But X-rays are so energetic that they can blast electrons right off the atom – they are what’s known as ionising radiation.
Of itself, ionisation is a very common process. It happens, for instance, when salt is dissolved in water – so the fluids in your body contain plenty of ions. But when ionising radiation hits cells in the body it can create free radicals; highly reactive molecules that increase the risk of cancer. (The body’s natural defence against free radicals is antioxidants, which is why foods with antioxidants in are often advertised as good for your health, though all the evidence is that antioxidants you consume don’t join forces with your internally produced ones, so have no benefit.)
The danger of ionisation in your body created by the high energy photons means that it’s best to avoid excessive exposure to X-rays, which is why radiographers operate from behind a protective screen. But the levels we are exposed to as patients are very low-risk, especially bearing in mind the natural radiation we are exposed to all the time. There is always a certain amount of radiation in the air around us from natural sources. A chest X-ray, for example, is about the same level of radiation as the extra natural radiation you are exposed to by taking a ten-hour flight.
Cats and nuclear resonance
To discover what is going on inside your body without cutting it open, doctors now have a much wider range of penetrating beams available to them. A CAT scan is still an X-ray, but one that goes far beyond anything that was possible before computers. It stands for ‘computer assisted tomography’ (or computerised axial tomography), which sounds a little scary when you realise that tomography is generally a matter of cutting things into very thin slices. But here it’s the X-ray image that produces a series of snapshot slices through the part of the body being examined. Heavy-duty maths (hence the ‘computer’ part of the name) transforms data from a range of angles into a detailed, multi-layered image.
The other well-known scanner is MRI, standing for magnetic resonance imaging. It was originally called NMR, with the ‘N’ short for nuclear, but that first initial was dropped because of the association of ‘nuclear’ with nuclear radiation. This was an unnecessary fear, as the name simply means that the nuclei of atoms in the scanned person’s body are being observed. The patients aren’t bombarded with radiation.
The protons in the nuclei of atoms can act like little magnets. MRI uses a strong magnetic field to get the magnetic fields of some of the protons in water molecules to line up. The scanner then uses a burst of radio. Radio is a relatively low-energy form of light, and if the radio photons have just the right energy they can give the little proton magnets a brief flip of the direction of their spin. The flipped protons rapidly fall back and produce their own photons, which can be detected. Because different types of tissue and different levels of blood flow produce different outputs it is possible to distinguish between them when the emitted photons are detected by the scanner.
Hunting the elusive neutrino
Photons of light of appropriate energies aren’t the only particles that can pass through solid matter. Every second about 50 trillion particles called neutrinos pass through your body. These particles are emitted by the Sun and other nuclear sources. Neutrinos are very slippery customers. They are so difficult to detect that although theory predicted their existence in the 1930s, neutrinos weren’t actually spotted for over twenty years. In an experiment at CERN in Geneva in 2011, these particles were thought to be discovered travelling faster than light, with claims that Einstein’s theory of relativity would fall apart if something could do this.
Because of the ease with which they pass through your body, it might seem neutrinos would be great for medical scans – the trouble is that no part of your body is much of a barrier. Neutrinos have little more problem getting through you than empty space. In fact most neutrinos pass through the whole Earth as if it wasn’t there. The only reason we can detect them at all is that just occasionally one of them will collide with an atom or molecule and will generate a little spray of other particles – we never see the neutrinos themselves.
Neutrino ‘telescopes’ are usually situated in mines a couple of miles underground, where hardly anything else is likely to get through and set off reactions in the vats of cleaning fluid, or similar materials, that are used as detectors. Such a device has been used to produce a neutrino picture of the Sun. It’s very blocky – just a few pixels – and it’s typical of neutrinos that the Sun was the opposite side of the Earth at the time.
The most dramatic neutrino detector is the IceCube observatory at the South Pole. This remarkable device, completed in April 2011, uses a square kilometre of ice as its detection medium, with detectors buried nearly 2.5 kilometres down looking for tiny flashes where incoming neutrinos collide with the ice above. The ice acts as both the barrier to other particles causing false signals and as a detection medium – there’s something rather spooky about the thought of tiny flashes deep in the Antarctic ice revealing neutrinos from distant nuclear reactions in space.
The neutrinos light couldn’t catch
The CERN discovery will probably prove to be a storm in a teacup. The experiment involved sending neutrinos down a distance of 732 kilometres (this incidentally has nothing to do with CERN’s most famous experiment, the Large Hadron Collider). At the end of the journey, the few neutrinos that would be detected were discovered to have arrived 0.00000006 seconds earlier than they should have. By far the most likely reason for this is that the distance measurement was wrong. At the time of writing this result had not been duplicated elsewhere.
Failing that, the next most likely explanation is that the neutrinos were bending the rules. It’s wrong to suggest, as so many articles did at the time, that modern physics somehow depends on nothing being able to go faster than light. Special relativity says that this won’t happen as a rule, but it is possible to get around the ‘barrier’. In fact we already have well-established experiments in which particles travel faster than light speed.
This is a consequence of quantum mechanical tunnelling. One of the strange aspects of quantum physics is that particles don’t have an absolute location, just a probability of being in various places. This means that particles can jump through an obstacle without passing through the space in between.
This sounds like something obscure and unusual, but it’s how the Sun (or any other star) works. For nuclear fusion to take place, positively charged protons have to be pushed incredibly close together – so close that even the temperatures and pressures in the Sun aren’t enough to get the reaction going. The Sun only works because every second billions of particles tunnel through the barrier of the repulsion and fuse.
That same tunnelling technique has been used to send particles faster than light. All the evidence is that a tunnelling particle doesn’t travel through the space in ‘tunnels’ through – instead it disappears at one side and instantly reappears at the other. So if you imagine a photon going 1 centimetre at the speed of light, tunnelling 1 centimetre instantly and going a further centimetre at the speed of light, it will have traversed the entire distance at one and half times the speed of light – 1.5c where ‘c’ is the speed of light.
I’m not saying this is what is happening in the neutrino experiment, but I do imagine that the cause will be something similar. Not a collapse of special relativity, just a way around it. That’s if it’s not experimental error, which still seems most likely. Special relativity has been tested so many times and has always delivered.
Either way, neutrinos won’t be joining the medical toolkit used to explore your body any time soon, but with the work of facilities like IceCube, they are of interest to astronomers. In exploring the universe, just as in investigating the innards of your body, it’s light that reigns supreme. Light is our ultimate vehicle for exploring space, near and far, and it’s one that your body is adept at handling.