RATHER than overstate the implications of our little parable we will understate them. We do not say that the parable proves or disproves any theory. An analogy never does either. But at least our story shows this. To say that a living organism is a "mere machine" is to say a great deal. How much will, no doubt, be realized with particular force by an engineer who knows what skill and thought go to the making of a machine, but everyone will agree that this analogy presents us with a problem of some magnitude. lf living organisms are more than machines there is more of a problem, but the lesser one is quite sufficient to claim our attention for a while.

The mechanical analogy can be illustrated by any example we care to choose. Let it be the governor of a steam-engine. This rotates with a velocity proportional to that of the engine. It is provided with weights which move outwards under the influence of centrifugal force and are restrained by gravity or a spring. At any given speed these weights take up such a position that the centrifugal force and the restraining force balance. The governor is connected by a system of rods and levers to a valve controlling the amount of steam admitted to the engine cylinder. When the speed begins to rise, the weights move further outward reducing the valve-opening and therewith the supply of steam. When the speed begins to fall, movement in the opposite direction increases the amount of steam admitted to the cylinder. In either case the previous speed is nearly restored. A tendency for the speed to change is generally due to a change in the work required of the engine, technically known as the load on it. The function of the governor is, therefore, to compensate for any change in load by a corresponding change in steam supply. The running of an engine would be irregular or, in engineering terms, unstable, if the engine were not fitted with this correcting device.

A creature supported on legs above the earth is naturally somewhat unstable and would fall over unless fitted with devices designed to maintain an upright position. These are situated in the ear where three semi-circular canals are arranged at right-angles to each other. These canals contain nerve endings which record movements of the hquid in them. When the head is tilted there is a change and a notification of this change is passed by nerve impulses to the brain. Here a test is made to check whether the head alone is tilted or the whole body, and if it is shown to be necessary, impulses are sent out through other nerves to those muscles which are required to restore balance. When these respond, the tendency to fall over is counteracted. Thus the function of the semi-circular canals in the labyrinthine organ of the ear is to compensate for any tendency towards loss of balance by a corresponding muscular effort. The process by which this function is performed is, as we know from experience, quite unconscious. It is research into this process which Hogben tells us "has disquieting conse- quences" and "overthrows the system of Kant".

A regulating action in physiology may result not from. mechanical, but from chemical change. An example is the involuntary deepening and quickening of respiration which occurs during muscular exertion. As a result of the increased rate of fuel consumption needed to supply the greater demand for energy, there is an increase in the amount of carbon-dioxide in the blood. To compensate for this, a part of the mid-brain known as the respiratory centre acts as a regulating device. This centre is bathed by the blood, and hence receives samples of it continuously. The respiratory centre sends impulses via the spinal cord and the nerves connected with it, to the respiratory muscles. These in turn are stimulated to greater activity, causing the lungs to exhale more carbon-dioxide, and to inhale more oxygen, until a normal concentration is restored.

Every text-book on physiology abounds in similar examples which demonstrate the close analogy between living organisms and machines. In both engineering practice and biology innumerable devices are to be found in which an initial disturbance sets up a complicated series of changes. These may be of a physical or chemical nature and may affect parts of the system remote from the scene of the initial disturbance. The successive events are causally linked to each other and serve the same general purpose, both in animate and inanimate mechanisms, namely to maintain the system in its proper working condition. Sometimes a tendency to depart from a predetermined performance is instantly corrected. Sometimes an organ increases or changes its activity to compensate for failure of some other organ. In extreme instances one organ may assume the duties of another, as in an automatic electric substation one machine may take over the duties of another which has become damaged.

Compensating and adjusting functions can only be performed both by engineering devices and living organs because their component parts are dehcately poised. A mechanism which can be easily set into operation must be responsive to a slight displacement. For perfect speed control the engine governor must be sufficiently unstable to be easily disturbed. This responsiveness is called sensitiveness in engineering and threshold value in physiology. It differs for different parts of the body and for different kinds of disturbance. The eye has a low threshold value for visible light, while the hide of a rhinoceros has a high one for almost any kind of applied force.

Our more elaborate and sensitive engineering devices are necessarily not only delicately poised, but also somewhat fragile. An automatic telephone exchange, for instance, is so susceptible to external influence that it requires an even temperature, dry atmosphere and the scrupulous exclusion of any dust. Thus anyone farnihar with machinery can readily understand why living organisms are so highly vulnerable. Were they not, their tissues would not be capable of the quick, sensitive, pervading flutter of response to external influence which is necessary in order that the organism may be preserved from destruction. One reason why the highly unstable configurations constituting living bodies are not easily upset is, paradoxically, their very instability. Thus vulnerability is once again proved to be one of the characteristics which marks the resemblance between living and non-living mechanisms.

This resemblance is, of course, not perfect, for we do not confuse the one with the other; machines are, for instance, constructed of component parts which are in themselves homogeneous, stable and solid, such as the bedplate, casing, cylinder, pistons and connecting-rods of a steam-engine. But the component parts of a living organism are each so small that the whole appears non-homogeneous and unstable throughout. This need not surprise us unduly. For a machine generally serves only one purpose while the various parts of a living body jointly serve more purposes than it is possible to enumerate. How so much can be packed into so little space baffles the imagination. We are inclined to admire the skill which goes to making a lady's small wrist-watch. But the simplest and smallest living thing performs many more functions than a watch. Some viruses are so minute that their bodies may span less than a score of molecules, yet these tiny specks of matter possess all the devices necessary to ensure that their unstable configurations shall not be upset and they contain, in addition, the mechanisms of nutrition and reproduction. The component parts of such mechanisms must obviously be near atomic dimensions. It is difficult to imagine any machine designed to the scale on which all organic devices are constructed.

Moreover, living bodies are able to perform functions that no machine so far invented is capable of. Among these are metabohsm, reproduction and the healing of wounds as well as the capacity of an organism to render itself immune against attacking forces. When a piece of machinery is knocked about it becomes less capable of withstanding further ill-treatment. But living bodies often become more able to resist disturbing influences after they have been exposed to them. The effect of the sun's rays is to render the skin less susceptible to sunlight, and many infectious illnesses can only be caught once.

Materialists tell us not to conclude that these differences have much philosophical significance. They point out that there is no known reason why, for instance, immunization should not be possible in the engineering world. That no machine has yet been invented capable of performing this function on itself does not prove that one could not be produced under the application of sufficient skill and ingenuity. Machines exist to-day which would have appeared impossible a generation ago. What inventions the future may bring, no man knows. This consideration leads materialists to the conclusion that any differences which we may observe between living bodies and machines are not fundamental and qualitative, but only differences of degree. Their view might be expressed picturesquely by saying that living organisms are like macliines, only more so.

This difference in degree can be allowed for without sacrificing any part of the analogy which mechanists stress, by letting only a part of the body correspond to any one machine. The brain alone has been compared by physiologists to a telephone exchange. Glands can be said to correspond to chemical factories. Thus we are able to stretch the mechanical analogy so as to make it even more apt without altering anything essential in the mechanist's argument. On the larger scale thus provided the whole body is more suitably described as equivalent to a town. Indeed, when we come to think about it a town seems so apt an analogy that we are inclined to wonder why the doctrine now known as "mechanism" has not been called "urbanism" instead.

A town with its multitudinous activities, its busy comings and goings, offers an unlimited number of points of resemblance to a living organism. Atoms of hydrogen, carbon, nitrogen, oxygen are like bricks, the principal building materials. The cells are like houses. Veins and arteries serve a similar purpose to streets, while capillaries are the counterparts of alleyways and passages. As blood carries its varied load of sugar, oxygen, carbon-dioxide and much else, so do motor-lorries transport goods required for the activities of a town. Hormones are dehvered to their required destinations like letters, nerves act as telephone wires, the brain as the above-mentioned central exchange; phagocytes are like policemen; carbon-dioxide is ejected through lungs as through chimneys; organs meet their needs from substances stored in the tissues as households do from shops; cells are born and cells die just as new houses are built and old ones pulled down; living bodies grow and change their shape, and so do towns. One could go on almost indefinitely drawing comparisons.

There are differences of degree. In a town, buildings are fairly durable, but living tissues are continuously falling to pieces and being repaired. In a town resembling a living body in this respect, the labour of keeping houses in repair would be enormous. Many thousands of tons of building materials would pass daily down each street, the railways and goods yards would handle an incredible volume of traffic.

Moreover the laws of biology are rigid indeed compared with those governing the conduct of any town. If the latter laws were prescribed by the most tyrannous autocracy, they would still appear liberal by contrast with the rigid ones which define the behaviour of every morsel of substance in a living organism.

Another difference is in the mode of control. Let us imagine a town which is as close as possible a counterpart of a living organism. Could we visit such a town we should be amazed at its activity, but we should be even more puzzled to see letters and parcels correctly delivered, although they had no addresses inscribed on them. The transport system would work to a perfect time-table of which we could not procure a copy because none would exist. As fast as wardrobes and .fireplaces tumbled out of the flimsy houses, others would be cast up by some propelling means with so perfect an aim that they would fit exactly into place. Hurricanes that swept the town and left the streets full of debris would blow in so strange a way that new bricks and doors and chimneys were carried off their lorries and placed exactly in position where needed to repair the damage. And in this fantastic town of nightmare bustle, we should not see, feel or hear any postmen, bricklayers, mayor, councillors, telephone operators, engine drivers, clerks or persons of any sort or description. There would be nothing to show how doors came to drop so accurately on to their hinges, roofs were mended, right numbers put through the telephone exchange, railway vans off-loaded at their proper sidings. Any student of physiology can confirm that the picture presented by no means overstates the facts.

Much of this has been pointed out by mechanists, and since they nevertheless prefer to say that living organisms are mere machines rather than that they are mere towns, we shall accept their more limited analogy. In some respect - which we have not appreciated the wider one may go further than a mechanist could countenance. Anyhow the resemblance of living organism to machines suffices to illustrate the point we wish to make. This is that for a machine and anything which resembles a machine the laws of physics and chemistry do not suffice to describe that which determines its structure and behaviour. To say that a thing is a mere machine is to say that it is more fully determined than any structure which results only from the unaided action of Matter on Matter.

We know a machine from a rough piece of untouched inorganic nature because its component parts are carefully shaped; because they fit neatly together; because they make up a delicately balanced system which goes on being delicately balanced; because they serve a specific purpose; because they provide evidence of the skill and ingenuity which went to their making. In all these respects a living body differs still more from a rough piece of untouched inorganic nature. Its parts are more carefully shaped, they fit more neatly together, they make up a more delicately balanced system, they serve a greater number of specific purposes, they convey, rightly or wrongly, the impression of a greater degree of skill and ingenuity in their design and production. Though, therefore, a machine may not be a perfect analogy to a living body, it is a far better one than any other to be found in the world of lifeless things. Indeed, anything which is less than a machine is not a suitable analogy at all.

Mechanists claim that this resemblance supports their doctrine. The reasoning which has led to this claim is surely one of the oddest things in the history of thought. For what does the mechanist theory say? It says that living bodies are in all essentials indistinguishable from the rough, untouched world of lifeless things, that they are entirely due to the uncoordinated forces operating in the Material Universe, that, like rocks and clouds and stars, they originate by the unaided action of Matter on Matter.

We should expect the mechanist to support this theory by pointing an analogy to rocks, or stars, or clouds, or perhaps to crystals, or rivers or atoms, to something belonging without a doubt to the rough, untouched world of lifeless things. If he did this we could follow his reasoning, even if we thought the resemblance only slight. But the mechanist does not do this. He says that living organisms are a part of the rough, untouched world of lifeless things because they are even less like this world than machines are. He says that living organisms are due to nothing but the unco-ordinated forces of Nature, because they resemble objects which are due to the carefully co-ordinating powers of Man.

"As the cat possesses a labyrinthine organ analogous to the product of human effort", the mechanist argues in effect, "we may be sure that the cat's body just happened like anything untouched by human effort. Living creatures move about and do not get smashed up. Motor-cars also move about and do not get smashed up if they have careful drivers inside them. But they do get smashed up if they are driverless. Therefore, living creatures are analogous to driverless motor-cars."

Surely this is the kind of logic which was taught in the Colleges of Unreason in the country of Erewhon described by Samuel Butler.

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