Are the Planets Inhabited?

ence with men. But "men" presuppose the existence of living organisms of inferior grades. Therefore a world

is sufficient that we know from experience that life does exist here; and in whatsoever way it was firs

s, or amongst the latter, between plants and animals. These are important subjects for discussion, but they do not affect

hey perish. We can, to a varying degree, determine the physical conditions prevailing upon the heavenly bodies, and w

first essential approximation, it indicates the continuance of the whole, with the unceasing change of the details. Were this definition complete, a river would furnish us with a perfect example of a living orga

h zone that is faintly luminous; and beyond this again, the broad spread of the two wings that are brightly luminous. The flame, like the river, preserves its identity of form, while its constituent details-the gases that feed it-are in continual change. But there is not only a change of material in the flame; there is a change of condition. Everywhere the ga

engine; so far the illustration is analogous to that of the gas flame. But the engine carries us a step further, for part of the material supplied to it is water, which is converted into steam by the heat of the fire, and

into itself non-living matter, converting it into an integral part of the organism, and so endowing it with the qual

and their inorganic surroundings. Without cease certain substances are taken up and disappear in the endless round of chemical reactions in the cell. Other substances which have been produced by the chemical reactions in living matter pass out of the cell and reappear in inorganic nature as waste products of the life process. The whole complex of these chemical transformations is generally called Metabolism. Inorganic matter contrasts strikingly with living substance. However long a crystal or a piece of metal is kept in observation, there is no change of the substance, and the molecules remain the same and in the same number. For living matter the continuous change of substances is an indispensable condition of existence. To stop the supply of food material for a certain time is sufficient to cause a serious lesion of the life process or even the death of the cell. But the same happens when we hinder the passing out of the products of chemical transformation from the cell. On the other hand, we may keep a crystal of lifeless matter in a glass tube carefully

he whole what we call life is nothing else but a complex of innumerable

neral. It is that special process of the circulation of matter which we call metabolism,

nds which these five elements form with each other are most complex and varied, and they also admit to combination-but in smal

l structure. "However differently the various plasma substances behave in detail, they always exhibit the same general composition as the other albuminoid

d jelly, or solution of glue. Just as we find the latter substance in all stages between the solid and the fluid, so we find in the case of protoplasm. The cause of this softness is the quantity of water contained in the living matter, which generally amounts to a half of its volume and weight. The water is distributed between the plasma molecules or the ultimate particles of living matter in much the same way as it is in the crystals of salts, but with the important difference that it is very variable in quantity in the plasm. On this depends the capacity for the absorption or imbibition in the plasm, and the mobility of its molecules, which is very important for the performance of the vital actions. However,

hey should be built up of chemical compounds that are most complex and unstable. "Exactly those substances which are most important for life possess a very high molecular weight, and consequently very large molecules, in comparison with inorganic matter. For example: egg-

ty, a living individual, wherein highly complex and unstable compounds are unceasingly undergoing chemical reactions, a metabolism essentially a

the basis of life must itself also in like manner be infinitely broad and infinitely varied. In this they are mistaken. As we have seen, the elements entering into the composition of organic bodies are, in the main, few in number. The te

nous matter and water, and the protoplasm can only take from without material dissolved in water; it can only eject matter in the same way. This osmosis i

y confined within this range, and therefore we are apt unconsciously to assume that this range is all the range that is possible, whereas it is but a very small fraction of the range conceivable, and indeed existing, in cosmical space. In its liquid state water is a general solvent, and yet pure water is neutral in its qualities, both characteristics being essential to its usefulness as a vehicle for the protoplasmic actions. Naturally, this function of water as a solvent can only exist when water is in the liquid state; solid water, that is ice,

onvert inorganic matter to their own use; they can only assimilate organic material. The plant, on the other hand, unlike the animal, can make use of inorganic material. Plant life, therefore, requires an abundant supply of water in which the various substances necessary for its s

f water that constitutes the oceans. It does not exist in the heart of the rocks forming the body of the planet nor in the void of space surrounding it outside the atmosphere. As the Earth condensed from the original nebula, and cooled and solidified, a certain quantity of matter remained at its surface in the form of free gases and unstable compounds, and, within the narrow precin

offer no home for the living organism; least of all for the highest of such organisms-Man. Both must be tempered t

iate being was spread between him and its darkness, in which were joined, in a subdued measur

had to be spread of intermediate being;-which should appease the unendurable glory to the level of human feebleness, and sign the changeless motion of the heavens with the semblance o

The cloud, that is to say water-vapour, is necessary because the plant in its turn cannot directly assimilate to itself the nitrogen from the atmosphere. The food for the plant is brought to it by water, and it assimilates it by the help of water. It is, t