by John Carey
We intoxicated them with pure oxygen and then tried the salts, but with the same result. Finally, by administering the salts in minute quantities and very slowly, we were able to preserve some uneviscerated specimens, but none with the head extended.
Source: John Steinbeck, The Log from the Sea of Cortez, London, Heinemann, 1958.
Telling the Workers about Science
J. B. S. Haldane (1892–1965) was a child prodigy. At three, it is claimed, he asked, on looking at blood from his cut forehead, ‘Is it oxyhaemoglobin or carboxyhaemoglobin?’ Because of his precociousness he was savagely bullied at Eton, which turned him against authority for life. In the 1930s he became an ardent Communist, visiting Spain during the Civil War to observe the effects of Fascist aerial bombardment.
As a student at Oxford he switched from maths to Classics, in which he got a first class degree. He had a wide knowledge of literature and a huge memory for English poetry. In the First World War he was commissioned into the Black Watch, earning the nickname ‘Bombo’ for his experiments with bombs and grenades.
After the war, as a don at New College, Oxford, he became a member of Lady Ottoline Morrell’s Garsington Manor set, meeting writers of the day – Katherine Mansfield, Lytton Strachey and Aldous Huxley, who satirized him as Shearwater in Antic Hay. Encouraged by his first wife, a journalist, he began writing the popular scientific articles for the Manchester Guardian and the Daily Worker for which he is best known. As a scientist, his main interest was in applying genetics to evolution theory, to show how evolution worked mathematically, and he became the first Professor of Biometry at University College London in 1937.
Of the two articles that follow, the first is from Haldane’s first collection, Possible Worlds (1927) and the other explains nuclear fission to readers of the Daily Worker in 1939.
On Being the Right Size
The most obvious differences between different animals are differences of size, but for some reason the zoologists have paid singularly little attention to them. In a large textbook of zoology before me I find no indication that the eagle is larger than the sparrow, or the hippopotamus bigger than the hare, though some grudging admissions are made in the case of the mouse and the whale. But yet it is easy to show that a hare could not be as large as a hippopotamus, or a whale as small as a herring. For every type of animal there is a most convenient size, and a large change in size inevitably carries with it a change of form.
Let us take the most obvious of possible cases, and consider a giant man sixty feet high– about the height of Giant Pope and Giant Pagan in the illustrated Pilgrim’s Progress of my childhood. These monsters were not only ten times as high as Christian, but ten times as wide and ten times as thick, so that their total weight was a thousand times his, or about eighty to ninety tons. Unfortunately the cross sections of their bones were only a hundred times those of Christian, so that every square inch of giant bone had to support ten times the weight borne by a square inch of human bone. As the human thigh-bone breaks under about ten times the human weight, Pope and Pagan would have broken their thighs every time they took a step. This was doubtless why they were sitting down in the picture I remember. But it lessens one’s respect for Christian and Jack the Giant Killer.
To turn to zoology, suppose that a gazelle, a graceful little creature with long thin legs, is to become large, it will break its bones unless it does one of two things. It may make its legs short and thick, like the rhinoceros, so that every pound of weight has still about the same area of bone to support it. Or it can compress its body and stretch out its legs obliquely to gain stability, like the giraffe. I mention these two beasts because they happen to belong to the same order as the gazelle, and both are quite successful mechanically, being remarkably fast runners.
Gravity, a mere nuisance to Christian, was a terror to Pope, Pagan, and Despair. To the mouse and any smaller animal it presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only to a hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.
An insect, therefore, is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble. It can go in for elegant and fantastic forms of support like that of the daddy-long-legs. But there is a force which is as formidable to an insect as gravitation to a mammal. This is surface tension. A man coming out of a bath carries with him a film of water of about one-fiftieth of an inch in thickness. This weighs roughly a pound. A wet mouse has to carry about its own weight of water. A wet fly has to lift many times its own weight and, as every one knows, a fly once wetted by water or any other liquid is in a very serious position indeed. An insect going for a drink is in as great danger as a man leaning out over a precipice in search of food. If it once falls into the grip of the surface tension of the water – that is to say, gets wet – it is likely to remain so until it drowns. A few insects, such as water-beetles, contrive to be unwettable, the majority keep well away from their drinks by means of a long proboscis.
Of course tall land animals have other difficulties. They have to pump their blood to greater heights than a man and, therefore, require a larger blood pressure and tougher blood-vessels. A great many men die from burst arteries, especially in the brain, and this danger is presumably still greater for an elephant or a giraffe. But animals of all kinds find difficulties in size for the following reason. A typical small animal, say a microscopic worm or rotifer, has a smooth skin through which all the oxygen it requires can soak in, a straight gut with sufficient surface to absorb its food, and a simple kidney. Increase its dimensions tenfold in every direction, and its weight is increased a thousand times, so that if it is to use its muscles as efficiently as its miniature counterpart, it will need a thousand times as much food and oxygen per day and will excrete a thousand times as much of waste products.
Now if its shape is unaltered its surface will be increased only a hundredfold, and ten times as much oxygen must enter per minute through each square millimetre of skin, ten times as much food through each square millimetre of intestine. When a limit is reached to their absorptive powers their surface has to be increased by some special device. For example, a part of the skin may be drawn out into tufts to make gills or pushed in to make lungs, thus increasing the oxygen-absorbing surface in proportion to the animal’s bulk. A man, for example, has a hundred square yards of lung. Similarly, the gut, instead of being smooth and straight, becomes coiled and develops a velvety surface, and other organs increase in complication. The higher animals are not larger than the lower because they are more complicated. They are more complicated because they are larger. Just the same is true of plants. The simplest plants, such as the green algae growing in stagnant water or on the bark of trees, are mere round cells. The higher plants increase their surface by putting out leaves and roots. Comparative anatomy is largely the story of the struggle to increase surface in proportion to volume.
Some of the methods of increasing the surface are useful up to a point, but not capable of a very wide adaptation. For example, while vertebrates carry the oxygen from the gills or lungs all over the body in the blood, insects take air directly to every part of their body by tiny blind tubes called tracheae which open to the surface at many different points. Now, although by their breathing movements they can renew the air in the outer part of the tracheal system, the oxygen has to penetrate the finer branches by means of diffusion. Gases can diffuse easily through very small distances, not many times larger than the average length travelled by a gas molecule between collisions with other molecules. But when such vast journeys – from the point of view of a
molecule – as a quarter of an inch have to be made, the process becomes slow. So the portions of an insect’s body more than a quarter of an inch from the air would always be short of oxygen. In consequence hardly any insects are much more than half an inch thick. Land crabs are built on the same general plan as insects, but are much clumsier. Yet like ourselves they carry oxygen around in their blood, and are therefore able to grow far larger than any insects. If the insects had hit on a plan for driving air through their tissues instead of letting it soak in, they might well have become as large as lobsters, though other considerations would have prevented them from becoming as large as man.
Exactly the same difficulties attach to flying. It is an elementary principle of aeronautics that the minimum speed needed to keep an aeroplane of a given shape in the air varies as the square root of its length. If its linear dimensions are increased four times, it must fly twice as fast. Now the power needed for the minimum speed increases more rapidly than the weight of the machine. So the larger aeroplane, which weighs sixty-four times as much as the smaller, needs one hundred and twenty-eight times its horsepower to keep up. Applying the same principles to the birds, we find that the limit to their size is soon reached. An angel whose muscles developed no more power weight for weight than those of an eagle or a pigeon would require a breast projecting for about four feet to house the muscles engaged in working its wings, while to economize in weight, its legs would have to be reduced to mere stilts. Actually a large bird such as an eagle or kite does not keep in the air mainly by moving its wings. It is generally to be seen soaring, that is to say balanced on a rising column of air. And even soaring becomes more and more difficult with increasing size. Were this not the case eagles might be as large as tigers and as formidable to man as hostile aeroplanes.
But it is time that we passed to some of the advantages of size. One of the most obvious is that it enables one to keep warm. All warm-blooded animals at rest lose the same amount of heat from a unit area of skin, for which purpose they need a food-supply proportional to their surface and not to their weight. Five thousand mice weigh as much as a man. Their combined surface and food or oxygen consumption are about seventeen times a man’s. In fact a mouse eats about one quarter of its own weight in food every day, which is mainly used in keeping it warm. For the same reason small animals cannot live in cold countries. In the arctic regions there are no reptiles or amphibians, and no small mammals. The smallest mammal in Spitzbergen is the fox. The small birds fly away in the winter, while the insects die, though their eggs can survive six months or more of frost. The most successful mammals are bears, seals, and walruses.
Similarly, the eye is a rather inefficient organ until it reaches a large size. The back of the human eye on which an image of the outside world is thrown, and which corresponds to the film of a camera, is composed of a mosaic of ‘rods and cones’ whose diameter is little more than a length of an average light wave. Each eye has about half a million, and for two objects to be distinguishable their images must fall on separate rods or cones. It is obvious that with fewer but larger rods and cones we should see less distinctly. If they were twice as broad two points would have to be twice as far apart before we could distinguish them at a given distance. But if their size were diminished and their number increased we should see no better. For it is impossible to form a definite image smaller than a wave-length of light. Hence a mouse’s eye is not a small-scale model of a human eye. Its rods and cones are not much smaller than yours, and therefore there are far fewer of them. A mouse could not distinguish one human face from another six feet away. In order that they should be of any use at all the eyes of small animals have to be much larger in proportion to their bodies than our own. Large animals on the other hand only require relatively small eyes, and those of the whale and elephant are little larger than our own.
For rather more recondite reasons the same general principle holds true of the brain. If we compare the brain-weights of a set of very similar animals such as the cat, cheetah, leopard, and tiger, we find that as we quadruple the body-weight the brain-weight is only doubled. The larger animal with proportionately larger bones can economize on brain, eyes, and certain other organs.
Such are a very few of the considerations which show that for every type of animal there is an optimum size. Yet although Galileo demonstrated the contrary more than three hundred years ago, people still believe that if a flea were as large as a man it could jump a thousand feet into the air. As a matter of fact the height to which an animal can jump is more nearly independent of its size than proportional to it. A flea can jump about two feet, a man about five. To jump a given height, if we neglect the resistance of the air, requires an expenditure of energy proportional to the jumper’s weight. But if the jumping muscles form a constant fraction of the animal’s body, the energy developed per ounce of muscle is independent of the size, provided it can be developed quickly enough in the small animal. As a matter of fact an insect’s muscles, although they can contract more quickly than our own, appear to be less efficient; as otherwise a flea or grasshopper could rise six feet into the air.
Atom-Splitting
This is a sensational article. I am sorry. In these articles I try to keep to facts. But occasionally facts are sensational. A discovery has just been made which may revolutionize human life as completely as the steam engine, and much more quickly. The odds are against its doing so, but not more than ten to one, if so much. So it is worth writing about it.
In the Daily Worker of March 30th, 1939, I described the recent work on splitting the nuclei of uranium atoms. A certain number of them explode when neutrons collide with them. Neutrons are among the so-called elementary particles – that is to say, particles which have not yet been broken up, such as electrons, protons, and perhaps a few others. This does not mean that they will never be broken up.
Ordinary atoms hold together when they collide at a speed of about a mile a second, as they do in air. When the temperature is raised and the speed of collisions goes up to ten miles or so a second, they cannot hold together, but electrons – that is to say, elementary particles with a negative charge – are torn off them. That is why a flame conducts electricity.
But at moderate speeds – say, a few thousand miles per second – collisions only break up the atoms temporarily. They soon pick up their lost electrons. When the speed rises to tens or hundreds of thousands of miles per second, the nuclei, or cores of the atoms, are sometimes broken up.
When a current is passed through the heavy variety of hydrogen at a voltage of half a million or so, the atomic nuclei become formidable projectiles, and if they hit a light metal called lithium they break up its atomic nuclei and let neutrons loose. Neutrons can penetrate the nuclei of many atoms even when moving slowly and cause still further changes.
Generally they only chip a piece off. But when they attack uranium, an element which is unstable, anyway, and produces radium, though very slowly, when left to itself, the uranium nuclei split up. The new fact, first discovered by Joliot and his colleagues in Paris, is that when the uranium nucleus splits, it produces neutrons also. In the experiments so far made, very small pieces of uranium were used.
So most of the neutrons, which can penetrate even metals for some distance, get out. But if the neutrons are liberated in the middle of a sufficiently large lump of uranium, they will cause further nuclei to break up, and the process will spread. The principle involved is quite simple. A single stick burns with difficulty, because most of the heat gets away. But a large pile of sticks will blaze, even if most of them are damp.
Nobody knows how large a lump of uranium is needed before it begins to set itself alight, so to say. But experiments are already under way in two British and one German laboratory to my knowledge, and doubtless in others in America, the Soviet Union and elsewhere.
In the current number [May 13th, 1939] of Nature Joliot and Halban, a French and a German physicist working together in Paris, published an S.O.S. letter sug
gesting means for slowing the process down, so as to avoid disaster.
If the experiment succeeds several things may happen. The change may take place slowly, the metal gradually warming up. It may occur fairly quickly, in which case there will be a mild explosion, and the lump will fly apart into vapour before one atom in a million has been affected. Or there may be a really big explosion. For if about one four-hundredth of the mass of the exploding uranium is converted into energy, as seems to be probable, an ounce would produce enough heat to boil about 1,000 tons of water. So i oz. of uranium, if it exploded suddenly, would be equivalent to over 100,000 tons of high explosive.
Of course, no one will begin with an ounce. Still, they may do a good deal of damage. Most probably, however, nothing much will happen. It may be, for example, that the majority of uranium atoms are stable, and only one of the several isotopes (as the different sorts of atom of the same element are called) is explosive. If so it will take several years to separate the isotopes.
Nevertheless, the next few months may see the problem solved in principle. If so, power will be available in vast quantities. There will be a colossal economic crisis in capitalist countries. There is plenty of uranium in different parts of the world, notably northern Canada, the Belgian Congo, Czechoslovakia and in several parts of the Soviet Union.