We can't exist without slime

What is your reaction to slime? Most people find the substance, and even the thought of it, distasteful and yet we would not be alive if it was not for slime in one form or another.

Slime consists of chemical polymers that expand on contact with water, producing a clear, sticky substance that is ubiquitous and which we recognise from its slipperiness and its ability to stick to surfaces. The compounds that make up slime are referred to as exopolymers, or EPS, by those that study them and they consist principally of carbohydrates and proteins, although many other chemicals may also be found in the EPS produced by different organisms. They are truly ubiquitous: bacteria using them to attach to substrates; single-celled algae release them when producing an excess of carbohydrate during photosynthesis; and multicellular organisms use them for protection, locomotion, to aid in feeding, to aid buoyancy, and as a means of attachment [1].

During evolution, some cells in multicellular organisms became adapted to have the sole function of producing the EPS that result in slime. These goblet cells (see above) discharge their contents to become hydrated and we are familiar with the resulting sliminess of animals like worms, slugs and fish. 

I talked about EPS to an audience of trout fishers and this was recorded by the Wild Trout Trust [2] and one of the illustrations is shown below, together with the link to the video. I could only give a very few examples, but you get the drift of my talk: EPS are everywhere and yet they are largely ignored, even by scientists who should know better. Of course, there are prejudices to be overcome and at one conference dinner I was given a special prize for "the most revolting talk" given during the sessions. An award made in good humour, of course, but indicating that the subject was one that most find unpleasant. This is a pity, because EPS are one of the most important families of chemicals known.

It is fair to say that humans would not exist if it was not for slime. This argument has two components: one that develops ideas on the evolution of humans and the other on the very important role slime plays in allowing our survival. Our most distant ancestors lived in water and left this medium when fish transitioned into the amphibians (and then into reptiles and mammals). Reptiles and mammals have body coverings that reduce the loss of moisture, something that is a threat to amphibians and also the first fish making visits to land. Anyone handling a fish is aware that they have a slippery covering and this protects the animal from attack by parasites and may aid locomotion: it is a feature that is retained by amphibians and serves to reduce water loss from their bodies when they are exposed to the air for long periods. It is also a common feature among soft-bodied terrestrial invertebrates such as worms and slugs, while others, like the arthropods, have an impervious exoskeleton that much reduces the threat of desiccation.

Fish slime protects the gills from abrasion and also provides a barrier against osmotic stress, a feature that is very important to salmon as they migrate from the sea to fresh waters. Yet gas exchange occurs from the water to the mucus and then to the tissue of the gill surface and this is a feature retained through the evolution of respiratory organs of amphibians, reptiles and mammals. Human lungs and nasal passages have a coating of mucus, moved by cilia that are a throwback to our very ancient protozoan ancestors, and it can be so plentiful that it has to be removed by blowing, coughing, or swallowing, the latter normally being a continuous and unconscious process. In addition to allowing gas exchange, this mucus acts as a trap for particles, both living and dead, and it is a convention that we blow an excess of the slime into handkerchiefs, often noting the extent of hydration once the mucus becomes dried, demonstrating admirably the extent to which the EPS had undergone considerable expansion when in contact with water. Larger quantities of slime than usual are produced when this first defence mechanism is triggered by infection.

It is not only nasal, and bronchial, tissue that produce mucus in humans, and other mammals, as slime is also found in the digestive tract and in the reproductive system. The slippery quality of mucus acts as a protection for the oesophagus and slime is produced elsewhere in the gut to allow smooth passage of the contents while protecting the wall of the digestive tract. The mucus is not broken down by enzymes and, when aqueous solutions of food chemicals are removed, characteristic compacted faeces result. These are bound with slime produced originally by the gut wall and also by EPS released by the many micro-organisms that are resident within the digestive tract; the microbes protecting themselves against digestion by secreting EPS that then become a binding material for the faeces.

The final use of slime in humans is in reproduction and, especially, in allowing the migration of sperm deposited within the female genital tract. Each sperm swims within seminal fluid that contains EPS and then traverses the cervical mucus and onwards into the uterus, where one sperm fertilises a waiting egg, if one is present. It should also be pointed out that mucus provides a lubricant to facilitate copulation. 

Vital rôles indeed and it is fair to say that we would not exist without slime in one form or another, nor would very many other organisms

Having read this far in the blog post, what are your reactions? Perhaps you agree that I deserve to be thought revolting in writing, and talking, about such things, even though I respect proper taboos in polite company? Yet I am only highlighting the remarkable diversity of uses for slime and EPS and this deserves to be much better known, rather than being given the "Ugh! response" that seems to be most people's reaction to the subject. Why do we feel that way?

[1] Roger S. Wotton (2005) The Essential Role of Exopolymers (EPS) in Aquatic Systems. Oceanography and Marine Biology: An Annual Review 42: 57-94.

[2] https://www.youtube.com/watch?v=XNN-NeSwQj0

Capital punishment and the tragedy of Edith Thompson

It is easy to kill micro-organisms, plants and invertebrates and even a pleasurable act when these cause infestations. I find it more difficult to kill many vertebrates, especially mammals and, when writing the blog post about Taking Life [1], my thoughts turned to the theoretical consideration of whether I could kill another human. The answer was a clear "No" and that extended to warfare, even when individuals are removed from their background and one has no knowledge of them, or of their family and friends. I'm not sure that I could live with the thought of having killed another human, even when my own life was threatened. It's not an assumption that I am keen to test.

As a result of my views on killing other humans, I am firmly against capital punishment, yet recognise that it is practised in many countries and has been for centuries. Indeed, one of the most famous examples of capital punishment occurred two thousand years ago with the crucifixion of Christ and the religion would not exist if Christ had not been killed and then risen from the dead. From this perspective, capital punishment is fundamental to Christianity and provides an exception to the moral code of the Judaeo-Christian tradition given by God in the Ten Commandments [2].

The crucifixion of Christ was carried out alongside that of two other "criminals" (omitted by Giotto in the fresco shown above) and it was intended as a spectacle, this being the custom of the time. Executions continued to be held in public in Western countries until recent times and they occur today in the Middle East and elsewhere, both as a warning and as a form of macabre entertainment. Of course, I refer here to state-sanctioned murder, rather than the execution by terrorists of hostages, or of citizens who are deemed to be out of line with a religious or political principle. Capital punishment is a deliberate act of killing, usually carried out weeks and months after a trial and, bizarrely, in countries like the USA, this delay can extend to decades.

Capital punishment requires an executioner (or executioners). Firing squads have traditionally involved a number of shooters, some of whom have live ammunition and others blanks. This lessens a sense of responsibility for taking life when the executioners are coerced into having to take part. In most other forms of capital punishment there is one executioner and they may be remote (as in lethal injection, gassing, or electrocution) or be involved directly (as in beheading, the use of the guillotine, and hanging). The latter executioners know only too well that they are responsible for taking the life of another human and do so legally.

Hanging remains one of the most frequently used forms of capital punishment and, while the act is usually witnessed by prison officials and some others, it is mostly carried out in private. In some high profile state killings, the execution has been recorded on film or video to serve as confirmation that the act has taken place, but this is exceptional. There is a tradition that hangmen used by the state (are there any hangwomen?) are selected for their knowledge and ability to ensure clinical dispatch and some learn these skills from within a family tradition of having the role, learning by stages until able to perform a hanging themselves. How are they affected by the experience?

The following quote is from a BBC article [3] that includes an interview with Sabir Masih, a hangman in Pakistan:

"I feel nothing. It's a family thing. My father taught me how to tie the hangman's knot, how many coils etcetera, and he took me along to witness some hangings around the time when I was being recruited."..

.."My only concern is to prepare him [the victim] at least three minutes before the time of hanging. So I remove his shoes, put a hood on his face, tie his hands and feet, put the noose around his neck, make sure the knot is placed below his left ear, and then wait for the jailer's signal to pull the lever."

There is no pre- or post-hanging psychological counselling for hangmen, and no limit to the number of hangings one executioner may perform before he is given a break.

Mr Masih says he doesn't need either.

Not all hangmen have that reaction and one the chief executioners in England, John Ellis, committed suicide because of the stress created by his job, and of one execution in particular. A reporter for The Rochdale Observer interviewed Ellis's wife shortly after his funeral and she mentioned the hanging of Edith Thompson, carried out by her husband on 9th January 1923 [4]. The execution, and its preliminaries, are described in the book Criminal Justice by René Weis [5] and the distinguished Shakespearean scholar describes the events leading up to Edith Thompson's conviction for the murder of her husband. It is a harrowing, and tragic, story and I found some sections of the book distressing to read. Despite the verdict of the court that she was guilty of murder, Weis shows us that this was a miscarriage of justice. 

Edith had brief, passionate encounters with Freddy Bywaters, a young merchant seaman, during his short return visits to England between voyages to Australia and the Far East, but it was Bywaters alone who killed her husband, Percy. In the photograph below, posed deliberately by Edith's brother, Edith is flanked by Percy on the right and by Freddy on the left - eighteen months after the photograph was taken all three would be dead. There is no dispute that Freddy killed Percy, although there has been discussion of the circumstances that led up to the assault and, to the end, Freddy maintained that Edith was innocent and had nothing to do with the final act.

Especially harrowing in Criminal Justice are the descriptions of the extreme anguish that Ethel suffered while on remand and when awaiting execution. In the weeks leading up to 9th January 1923 she was so distressed that frequent doses of strong sedative had to be administered and she was near unconscious when warders effectively carried her to the scaffold after Ellis had entered her cell to prepare her for the execution (was this his first contact with Edith after being summoned from Rochdale?). When the act took place, there were dreadful consequences, as the drop caused severe haemorrhaging and there was a lot of cleaning up to do. Ellis and the prison staff were obviously very upset by this and they may also have suspected that she was innocent of a capital offence. Several journalists took up both Edith's and Freddy's cases and argued against the verdict of the court and there was wide coverage of the case [5] and of subsequent events.

I won't dwell more on that story, but it is relevant to discussions on the use of the death penalty as a means of state punishment. If the cold-blooded nature of the act wasn't bad enough, the mental anguish of waiting for "justice", the agony of visits from family and friends as the day draws nearer, and the effect on all the staff are quite enough to convince me that capital punishment cannot be justified, even for the most heinous crimes.

 

                                                     Executed and executioner

   

[1] http://www.rwotton.blogspot.com/2015/08/taking-life.html

[2] The Holy Bible Exodus chapter 20 verse 13 (King James' Version).

[3] http://www.bbc.co.uk/news/world-asia-33773477

[4] http://www.noose.wg.vu/interview_w__a._ellis/

[5] René J. A. Weis (1990) Criminal Justice: The True Story of Edith Thompson. London, Penguin Books.

Taking Life

The headline on page 6 of The Independent on Saturday 1st August read [1]: 'What is fun about death and the killing of a beautiful creature?'. It was a quote from an interview by Jonathan Owen with the campaigner Virginia McKenna and focussed on the killing of a lion by a trophy hunter, but it set me thinking more widely about my attitude to killing organisms. I maintain that all creatures are beautiful, so, for me, the adjective is redundant.

I'll begin with two examples that only loosely fit the definition of a creature. As someone who has had a close encounter with E. coli (below, top left), I am very thankful for antibiotics and their power to kill the bacteria. However, studies in microbiology reveal not only a beautifully adapted organism, but one with tremendous powers of reproduction and the ability to fend off the defence mechanisms of the host. Killing them when they infect areas of the body other than the gut brings a great deal of relief but I wouldn't describe it as being fun. The same applies to the presence of weeds like dandelions in the garden, especially the lawn. No-one could dispute that they are beautiful plants, but we like them in the countryside and not messing up the neat arrangement of plants that we like to culture. Killing weeds never involves thoughts of regret at extinguishing the life of another creature, at least in my experience.

Having spent time in Northern Scandinavia on research visits, I know something about high densities of mosquitoes [2]: who was it who said they enjoyed the high-pitched noise of mosquito wing beats and likened it to singing? Adult females require blood before they can mature their eggs and they are both persistent at finding hosts and, despite their noisy flight, usually land unnoticed. Unfortunately, I react badly to mosquito bites and invariably get lots of itchy lumps as a result. Creams and anti-histamine sprays are of some assistance, but I try to kill the insects before attack, if at all possible. Not exactly the fun of the headline in The Independent, but certainly pleasurable. Yet I have studied larval mosquitoes in some detail, as I have the larvae of other biting flies, and I am amazed by the evolution of their feeding structures and the metamorphosis that results in such different body plans as those of the larvae and adults. I retain a sense of wonder, but this is not in my mind when I kill biting flies (and I've killed millions of their larvae). However, there are plenty left after my efforts.

Other beautiful creatures include wasps and blowflies (above, lower). All of us are amazed at the structure of wasp nests: the way they are constructed; the social behaviour of the inhabitants; and the capacity for workers to hunt and gather to bring food to bring to the nest. Wasps are brightly coloured to give a warning that they sting and we react to that, even though it evolved long before humans appeared on the Earth. Indeed, almost any insects with black and yellow striped abdomens receive the same treatment as wasps as we try to brush them away and, preferably, swat them. As I write, we have a wasp nest nearby and the workers often enter our house through open windows. Despite my admiration for the structure and lifestyle of wasps, I kill these intruders with relish and would ideally like the nest removed, wherever it might be. It's the same with blowflies and house flies and their beautifully adapted maggots [3]. I kill those with the same degree of pleasure.

All the examples thus far are of creatures which either cause harm or irritation to us, or to our immediate surroundings. What of the killing of creatures for food? Our hunter-gatherer ancestors captured animals to eat and we can still do this if collecting, fishing or shooting. However, we are now mostly dependent on buying animals that have been killed by someone else, although blue mussels are sold alive before we kill them by tipping them into a pan of boiling muscadet [4]. The food industry is geared to providing us not only with killed animals, but also gutted fish, or butchered meat, although this processing is largely hidden from us. Fish are caught at sea by lines or trawls, or gathered from large enclosures in fish farms, and they are allowed to die before being gutted and packed on ice. Meat comes mainly in the form of chickens, turkeys, sheep, cows and pigs that are farmed, with the latter three transported first to markets and then on to abattoirs for slaughter. I've visited an abattoir and it was not a pleasant experience, but not sufficiently unpleasant to stop me from being an enthusiastic omnivore.

During disease outbreaks, it is common for farm animals to be shot in situ and their carcases burned or buried. It strikes me that killing livestock on farms is preferable to the market-abattoir route, although many may prefer the killing to continue being hidden from view. At least some chickens and turkeys are killed on the farms where they are reared, but the conditions in which they live vary greatly. The intensive rearing of battery chickens for egg production is a case in point and I still remember vividly the smells, sounds and sights of a battery rearing unit that I visited forty years ago. Slaughter is just part of a brutal process, as it is with other intensively reared farm animals, and slaughter on site, or nearby, is hardly the compensation it would be for animals that are allowed a (relatively) free range. 

Shooting livestock would be little different to hunting game, something that I've enjoyed. As I do not wish to kill the animals myself, my role in rough shoots is as a beater, walking up the game and watching the dogs quartering the ground ahead of the line of guns. It is a good day out and worth it just to watch the dogs in action, and most birds on shoots I've attended are shot cleanly. In addition, there is the prospect of being paid for my pleasure in the occasional gift of a bird and I'm very fond of game of all kinds. My sole experience of hunting deer came when I accompanied a friend who is highly experienced stalker. We could see roe deer in a clearing and I was told to lie down and watch while he moved through the wood to get into a good position to shoot. After minutes, there was a loud crack and the deer dropped dead and we were quickly on to it. We immediately performed the gralloch, which was not upsetting to me as it was no different to the dissecting that I had done as part of my Zoology training. The deer was grazing one minute and dead the next and I thought that was rather good, just like the killing of pheasants that died shortly after they were put to flight.

Killing to prevent attacks, or for food, seems acceptable to me, as long as death is rapid. Killing for fun is less acceptable, although I recognise that some people get pleasure from slaughtering large numbers of fish and higher vertebrates, enjoying in this way their power over Nature. Selecting the killing of a lion, albeit in a gruesome manner, highlights our approach to the killing of all living creatures, each a remarkable example of the power of evolution.

[1] The Independent 1st August 2015 p6.

[2] http://www.rwotton.blogspot.com/2013/09/plagues-of-flies.html

[3] http://www.rwotton.blogspot.com/2014/06/why-drosophila-is-so-interesting.htm

[4] http://www.rwotton.blogspot.com/2014/03/moules-marinieres.html