Impartial thought comes to a conclusion about these phenomena different from that derived from anthropomorphic delusions. It does not try to smuggle dim, dark life into the collections of mercury molecules apparently obeying some inner impulse, or into the seeking or feeling about of a pseudopod of chloroform. On the contrary, it understands life as the play of natural forces under the conditions supplied by a living organism, as the automatic working of a machine-like apparatus to which natural forces supply the motive power. Similar manifestations in inanimate matter and in elementary organisms seem to justify the conclusion that the distinction between living and non-living matter is arbitrary, that there are only forces, or perhaps one single force, that is to say, one movement, in the universe, whose activity is manifested in the most manifold forms, of which life is one. Modern Monism has come to this conclusion, but it is not alone in so doing. Long before Monism there was a philosophy which conceived all cosmic energies to form a unity; and really it is only an obstinate quarrel about words, for the Hylozoists regard the universe as something living and ascribe life to all matter and all atoms of which matter is made up, while the Materialists regard life as a play of forces in matter. Fundamentally the Hylozoists and Materialists hold the same views, only that the former call force life and the latter call life force; just as the only point of difference between them and the Pantheists is that these have given the majestic title of God to the universal life they assume--as Spinoza has it, "_Omnia quamvis diversis gradibus animata sunt_." The question, what is life? is the greatest that the human understanding can ask of itself. For thousands of years man has cudgelled his brain over this, and is as far from finding an answer to-day as he was on the first day. The definition most often repeated runs thus: Life is the ability possessed by certain bodies to react to stimuli, to absorb nourishment and to reproduce themselves. That is a statement of observed facts, but it is no explanation. It informs us that we are familiar with bodies which behave in a way distinguishing them from other bodies; but why they conduct themselves differently from others, what the particular thing is which is present in certain combinations of matter and absent in others--that is an impenetrable secret.