The Faber Book of Science (62 page)

A muskrat, also called musquash, or technically,
Ondatra
zibethica
zibethica
Linn. 1766 – the creature didn’t give a hoot about nomenclature – fell into our swimming pool, which was empty except for a puddle of winter water. It huddled in a corner, wild frightened eyes, golden-brown fur, hairless muddied tail. Before I could find instruments suitable for catching and removing muskrats, a passing neighbour (unfamiliar with rodents
per
se,
or even with rodents living in Czechoslovakia since 1905), deciding he’d come across a giant rat as bloodthirsty as a tiger and as full of infections as a plague hospital, ran home, got his shotgun, and fired at the muskrat until all that was left was a shapeless soggy ball of fur with webbed hind feet and bared teeth. There was blood all over the sides and bottom of the pool, all over the ball of fur, and the puddle of water was a little red sea. The hunting episode was over, and I was left to cope with the consequences. Humankind can generally be divided into hunters and people who cope with consequences.

I buried the deceased intruder under the spruces in the backyard, and, armed with a bundle of rags, I went to clean up the shooting gallery. The swimming pool doesn’t have a drain, so the operation looked more like an exercise in rag technology, chasing the blood
north, south, east, west, up, and down. Chasing blood around an empty swimming pool is as inspirational as listening to a record of Haydn’s ‘Farewell Symphony’ with the needle stuck in the same groove, I became very intimate with the blood in that hour, and I began to daydream about it. The blood wasn’t just that unpleasant stuff that under proper and normal conditions belonged inside the muskrat. It was the muskrat’s secret life forced out. The puddle of red sea was, in fact, a vestige of an ancient Silurian sea. It was kept as an inner environment when life came ashore. Kept so that even – though it’s changed to a radically different concentration of ions, a different osmotic pressure, and different salts – the old metabolism hasn’t needed too much reshuffling.

In any case, the muskrat was cast ashore from its own little red sea. Billions of red blood cells were coagulating and disintegrating, their haemoglobin molecules puzzled as to how and where to pass their four molecules of oxygen.

The blood corpuscles were caught in tender, massive nets of fibres formed from fibrinogen, stimulated by thrombin that was formed from prothrombin. A long sequence of events occurred one after the other in the presence of calcium ions, phospholipids from blood platelets, and thromboplastin, through which the shot arteries were trying to show that the bleeding should be stopped because it was bad for the muskrat (though in the long run it didn’t matter). And in the serum around the blood cells, the muskrat’s inner-life signals were probably still flickering, dimming, and fading out: instructions from the pituitary gland to the liver and adrenals, from the thyroid gland to all kinds of cells, from the adrenal glands to sugars and salts, from the pancreas to the liver and fat tissues – the dying debate of an organism whose trillions of cells coexist thanks to unified information.

And, especially because of the final chase, the adrenalin and the stress hormone corticotrophin were still sounding their alarms. Alarms were rushing to the liver to mobilize sugar reserves, alarms were sounding to distend the coronary and skeletal muscle arteries, to increase heart activity, to dilate bronchioles, to contract skin arteries and make the hair stand up, to dilate the pupils. And all that militant inner tumult was abandoned by what should obey it. Then there were endorphins, which lessen the pain and anxiety of a warrior’s final struggle, and substances to sharpen the memory, because the struggle for life should be remembered well.

So there was this muskrattish courage, an elemental bravery transcending life.

But mainly, among the denaturing proteins and the disintegrating peptide chains, the white blood cells lived, really lived, as anyone knows who has ever peeked into a microscope, or anyone knows who remembers how live tissue cells were grown from a sausage in a Cambridge laboratory (the sausage having certainly gone through a longer funereal procedure than blood that is still flowing). There were these shipwrecked white blood cells in the cooling ocean, millions and billions of them on the concrete, on the rags, in the wrung-out murkiness. Bewildered by the unusual temperature and salt
concentration
, lacking unified signals and gentle ripples of the vascular endothelium, they were nevertheless alive and searching for whatever they were destined to search for. The T lymphocytes were using their receptors to distinguish the muskrat’s self-markers from non-self bodies. The B lymphocytes were using their antibody molecules to pick up everything the muskrat had learned about the outer world in the course of its evolution. Plasma cells were dropping antibodies in various places. Phagocyte cells were creeping like amoebas on the bottom of the pool, releasing their digestive granules in an attempt to devour its infinite surface. And here and there a blast cell divided, creating two new, last cells.

In spite of the escalating losses, these huge home-defence battalions were still protecting the muskrat from the sand, cement, lime, cotton and grass; they recognized, reacted, signalled, immobilized, died to the last unknown soldier in the last battle beneath the banner of an identity already buried under the spruces.

Multicellular life is complicated, as is multicellular death. What is known as the death of an individual and defined as the stoppage of the heart – or, more accurately, as the loss of brain functions – is not, however‚ the death of the system that guards and assures its individuality. Because of this system’s cells – phagocytes and lymphocytes – the muskrat was still, in a sense, running around the pool in search of itself.

Not to mention the possibility that a captured lymphocyte, when exposed to certain viruses or chemicals, readily fuses with a cell of even another species, forgetting about its previous self but retaining in its hybrid state both self and non-self information; it can last more or less forever there, providing the tissue culture is technically sound.

Not to mention the theoretical possibility that the nucleus of any
live cell could be inserted into an ovum cell of the same species whose nucleus has been removed, and after implantation into the surrogate mother’s uterus, the egg cell will produce new offspring with the genetic makeup of the inserted nucleus.

The shed blood shows that there is not one death, but a whole stream of little deaths of varying degrees and significances. The dark act of the end is as special and prolonged as the dark act of the beginning, when one male and one female cell start the flow of divisions and differentiations of cells and tissues, the activation of some hereditary information and the repression of some other, the billions of cellular origins, endings, arrivals and departures.

So in a way the great observer William Harvey was at least a little right when he called blood the main element of the four basic Greek elements of the world and body. In 1651 he wrote: ‘We conclude that blood lives of itself and that it depends in no ways upon any parts of the body. Blood is the cause not only of life in general, but also of longer or shorter life, of sleep and waking, of genius, aptitude and strength. It is the first to live and the last to die.’

Blood will have its way, I thought, wringing out another rag.

It is the colour of blood that makes death so horrible. People and other creatures (unless they happen to be the likes of a shark, hyena or wolf) have a fear of shed blood for this reason. It is a fear that hinders further violence when mere immobility, spiritlessness and
breathlessness
can’t. A fear that keeps the published photographs of a killing or slaughter from being true to life. The human reaction to the colour of blood is a faithful counterpart to the microscopic reality, the lethal cascade we so decently provoke by the final shot in the right place. There are an extraordinary number of last things in anyone’s bloodbath. Including a muskrat’s. And if any tiny bit of soul can be found there, there is not one tiny bit of salvation.

They say you can’t see into blood. But I think you can, if only through that instinctive fear.

Lucky for the Keres, the goddesses of bloodshed, that no one concerns himself with the microscopy of battlefields; lucky for the living that molecular farewell symphonies can’t be heard; lucky for hunters that they don’t have to clean up the mess.

To indicate the crucial nature of the nonclimatic effects of carbon dioxide, it is sufficient to mention the fact that a field of corn plants growing in full sunshine will completely deplete the carbon dioxide from the air within one meter of ground in a time of the order of five minutes …

Owners of commercial greenhouses discovered long ago that seedlings grow faster when the air in the greenhouses is enriched with
carbon dioxide. Many experiments have been done in growth chambers designed so that the carbon dioxide can be accurately controlled and the response of plants accurately measured. A typical experiment was done in 1975, measuring the effects of carbon dioxide on the growth and transpiration of leaves of the American poplar,
Populus
deltoides.
Experiments on other plant species usually give similar results. The poplar experiment used atmospheres ranging from one-tenth to three times the present outdoor concentration of carbon dioxide. The growth rate is zero at one-tenth of the outdoor level, rises rapidly as the carbon dioxide is increased up to the outdoor level, then rises more slowly as the carbon dioxide is increased to twice the outdoor level, then becomes constant as the carbon dioxide increases beyond twice the outdoor level. The saturation value of growth rate is one and a half times the rate at the outdoor level, and is reached at three times the outdoor level. So far, the results are unsurprising.

More surprising and of greater practical importance are the measurements of water transpiration in the poplar experiment. Transpiration means the loss of water by evaporation from the leaves. The rate of transpiration falls steadily as carbon dioxide increases, and is reduced to about half its present value when the carbon dioxide is enriched threefold. How is this decrease of transpiration to be explained? The essential point is that carbon dioxide molecules are rare in the atmosphere. They are hard for a plant to catch. The only way a plant can catch a carbon dioxide molecule is to keep open the little stomata or pores on the surface of its leaves, and wait for the occasional carbon dioxide molecule to blunder in. But the air inside the stomata is saturated with water vapor. On the average, about two hundred water molecules will stumble out of the hole for every one carbon dioxide molecule that stumbles in. The poplar experiment measured the water loss and the carbon gain of the leaves simultaneously, and found that the loss is a hundred times the gain when the carbon dioxide is at the outdoor level. The plant is forced to lose a lot of water in order to collect a little carbon dioxide. When the carbon dioxide in the atmosphere is enriched, the plant has a choice. The plant may either keep its stomata open and lose water as rapidly as before while increasing photosynthesis. Or it may partially close its stomata and reduce the loss of water while keeping photosynthesis constant. Or it may make a compromise, closing the stomata only a little, so that water loss is decreased while photosynthesis is increased.
The poplar leaves in the experiment chose the compromise strategy. Plants will in general choose whatever strategy they find optimum, depending on local conditions of temperature, humidity, and sunlight.

The moral of this story is that for plants growing under dry conditions, enriched carbon dioxide in the atmosphere is a substitute for water. Give a plant more carbon dioxide, and it can make do with less water. Since the growth of plants, both in agriculture and in the wild, is frequently limited by lack of water, the effect of carbon dioxide in reducing transpiration may be of greater practical importance than the direct effect in increasing photosynthesis. It is easy to measure both these effects of carbon dioxide in greenhouses and growth chambers. It is difficult to measure them in the real world out-of-doors. Here then is the crucial task for understanding the human dimensions of the carbon-dioxide problem. Our research programs must come to grips with the responses of crop plants and grasses and trees all over the world to increased carbon dioxide. To measure these responses, experiments in growth chambers are inadequate and computer simulations are useless. There is no substitute for field observations, widely distributed in place and extended in time.

If we can establish research programs, putting as much money and time and talent into the measurement of ecological responses to carbon dioxide as we are now spending on climatic effects, we may be able within a few years to answer the politically crucial questions. Is the direct effect of increasing carbon dioxide on food production and forests more important than the effect on climate? Is the human species already hooked on carbon dioxide, needing a continued increase of fossil fuel burning to fertilize our crops? When the coal and oil are all gone, shall we be burning limestone to keep the atmosphere enriched in carbon dioxide at the level to which the biosphere will have become addicted? I am not saying that the answers to these questions should be yes. But we must be aware that we do not have the knowledge to answer them with a confident no.