Natural Philosophy

by Wilhelm Ostwald

54. Life.

Among the bodies in our environment that are ponderable and have mass the animate beings are so strikingly distinguished from the inanimate that in most cases we have not the slightest doubt whether a body belongs to the one kind or to the other, even if in some cases we happen not to be familiar with its peculiar form. In the first place, therefore, we must answer the question in a general way and tell what the distinguishing peculiarities are that mark them off one from the other.

The first peculiarity is this, that living organisms are not stable but stationary forms. This distinction is based upon the fact that a stable form is at rest or unchangeable in all its parts, while a stationary body, though it seems unchangeable in its form, internally undergoes a constant change of its parts. Thus, a brass faucet is a stable body, since it not only preserves its form and function permanently, but consists at all times of the same material and shows the same peculiarities, such as stains, defects in form, etc. It cannot be said, it is true, that it will remain completely unchanged for all time. Its metal suffers a gradual chemical and mechanical deterioration. But this is not essential to the existence of the faucet, since the deterioration varies greatly with circumstances, and if conditions are ideal it can be reduced to zero.

On the other hand, the jet of water flowing from the faucet is a stationary body. In favorable circumstances it can assume a constant form, so that at a hasty glance it might be taken for a stable glass rod. On closer examination it will be found that the parts of water of which it is formed are not the same at any given instant as the instant before, each part that has flowed away being replaced by another just as large following it.

From this difference in the nature of the two bodies results a difference in their behavior. If I make a mark on the faucet with a file, the mark remains permanent. But even if I sever the entire water jet with a knife, the cut is healed the next moment, because by reason of the continuous flow of the water, the severed place is instantly eliminated from the body. Owing to this nature peculiar to stationary bodies, they have the capacity of being healed or of regeneration.

For a body to continue permanently in a stationary condition the material of which it is composed must be permanently supplied. If we turn off the faucet, the water jet immediately disappears or "dies." Evidently, therefore, a stationary body can subsist by its own means only if it has the property or capacity to provide itself continually with the necessary material. This material consists in the main of ponderable or chemical substances of definite physical and chemical properties, and thus the change of substance, metabolism, appears as a necessary property of the stationary body. In order, however, that metabolism should take place we must have free energy, or energy having the capacity to work, since it is only free energy that can cause substances to change, just as every phenomenon in the world implies the equalization of free energy. For a stationary body to exist independently, therefore, it must have the property of being able spontaneously to possess itself of the necessary substances and of free energy. But since, as we have already said, the energy of organisms is stored up and used in the main in the form of chemical energy, the two tasks which a stationary body has to perform, that of meeting the need for substances and for energy, are as a rule externally combined. In organisms these two necessities combined are called nutrition, and thus we recognize in the capacity for self-acquisition of nutrition another essential property of organisms.

A third essential property of organisms is the capacity for reproduction, for the bringing forth of similar beings. It is never impossible that the balance between the receipts and expenditures of a stationary body should, in consequence of some external causes, be disturbed, even when under normal conditions it possesses the property of self-nutrition. If the disturbance remains below a certain point, then, as we have already stated, regeneration sets in. But the disturbance may rise above that point, in which case the body ceases to exist, or dies. Then a similar body will not arise unless the manifold necessities that have led to the origin of the first will combine again to produce the second. That such a thing is possible, that, in fact, it often happens, is shown, for example, by the waves of the ocean, which have a stationary character since, while they are composed of constantly changing masses of water, their form remains unchanged. The waves are destroyed in the breakers, but arise again and again through the action of the wind upon the surface of the water. But the more complex such bodies are the less easily they are formed, while once they have been formed and have found the conditions of their existence, their preservation is much easier.

Beings, therefore, which have the capacity to form similar bodies out of themselves regularly and at the right time can preserve their species much more easily than those in which this property is absent. Death has to a great extent lost its power over beings capable of reproduction. By way of illustration let us take another stationary thing, a flame. A flame is not an organism because it is not self-sustaining. Yet it multiplies itself. And while a single little flame soon dies out, the sea of flame of a burning forest, which started from a single small flame, is well-nigh inextinguishable, and it cannot be fought in any other way than by letting it die its natural death and burn to the end.

Thus, while the fulfilment of the first two conditions, the stationary change and the self-supply of food, could produce bodies, which would be able to exist for a longer or shorter period, but which at some time would have to give way to other bodies of different form and nature, the capacity for reproduction creates the condition that forms of the same species continue to exist even after the existence of the individual has ceased.

These three properties constitute the essential characteristics of animate things or organisms.

That the organisms are all constructed upon the basis of chemical energy is a fact of experience which may be understood to imply that the other forms of energy are not capable of producing the above-mentioned conditions. This is due to the properties of chemical energy to which I have already called attention: its great concentration and, at the same time, its capacity for prolonged preservation. That chemical energy is the only form of energy suitable to life is obvious from the fact that in airship navigation, for example, the kinetic energy required for steering can be supplied only in the form of gasoline or hydrogen, that is, in the form of chemical energy, because any of the other forms would be much too heavy. The flight of a bee or the swimming of a dolphin cannot be conceived of except as brought about through chemical energy.

That this chemical energy is essentially that of carbon has also been established by experience, although it is not quite universal, for the sulphur bacteria found their household upon the energy of sulphur. The cause of the preference of carbon is again to be sought in its special fitness for the purpose, due, on the one hand, to its wide distribution, and, on the other hand, to the exceeding manifoldness of its combinations.

Finally, the construction of the organisms from a peculiar combination of solid and liquid substances can be proved to be equally due to technical relations.

These three last-named peculiarities are therefore to be regarded as the special characteristics of the organisms with which we are acquainted on the surface of the earth in the conditions there prevailing. We need not regard them conceptually as unchangeable or irreplaceable. But the first three characteristics, namely, the stationary nature, self-supply of nutrition, and reproduction, we may regard as the essential characteristics of organisms. They constitute the frame within which everything must be found which we should recognize as living in the widest sense.