It is possible that such similarities may be mere coincidences, but surely it is more reasonable to suppose that life in its operations may utilise, though it modify, the molecular affinities which produce the crystal. Life did not spring from crystallisation, but both alike. sprang in due order from natural antecedents; and if the spontaneous evolution of life, unlike crystallisation, no longer occurs, it is only because the requisite conditions of the former have passed away, while those of the latter have survived.

If we seek to know what the conditions of archebiosis, or lifebeginning, were, we must realise broadly what was the course of the earth's development chemically. In the earth's infancy chemical combination was rendered impossible by the intense heat which kept terrestrial matter in a state of dissolution. It has been calculated that the earth's temperature when it first started on its course as an independent planet was something like 3,000,000 degrees Fahrenheit, or about 14,000 times hotter than boiling water. As the mass grew cooler the affinities of certain molecules became just strong enough to overbalance the disruptive influence of heat and its allied forces, and the first and simplest chemical combinations then took place. It is obvious that such combinations would at first be very unstable, and would so continue till a cooler stage rendered them practically permanent, and called new combinations into being. At each repetition of the process a similar instability would attach to the newest combinations, while these combinations would gradually become more complex. Clearly, therefore, the stage of terrestrial formation from the earliest chemical combinations down to the hardening of the earth's crust must have been a period of enormous chemical activity. Nor is this all; for under the thermal conditions which heralded the appearance of life on the earth, many substances may, indeed must, have possessed properties which they no longer display. Experiment, even under present limitations, verifies the marvellous effects of heat, cold, and pressure. Heat will drive iron into vapour; cold will solidify or liquefy oxygen and other gases; and even hydrogen, the lightest of known substances, when subjected to a pressure of 650 atmospheres (about 9,533 pounds to the square inch), issued as a steel blue substance, and fell to the ground in solid drops which rang like a metal.12 But here we must bear in mind that absolute stability is unknown. The molecules of the most compact body are incessantly swinging to and fro, though the rate of their vibrations may vary. Now heat increases the impetuosity of this molecular rhythm till the point is reached at which cohesion is overpowered and disruption ensues. Any compound therefore under a temperature close upon the disruption point is in a very unstable or mobile condition. Now we are not in any way bound to conclude that the lowest forms of life discoverable at the present day are necessarily identical with the forms

12 Experiments by M. Raoul Pictet, of Geneva, in 1878.

which first appeared. But even protoplasm as known to us possesses a chemical constitution of considerable mobility.

And now, gathering up the threads of the argument, is it not possible to conjecture that life may have arisen in some such way as this? Colloid, no less than crystalloid, matter depends ultimately for its coherence on the polar groupings of its molecules. Given, therefore, colloid matter of a certain complexity, and a high mobility · caused by the thermal conditions of its environment, we may well suppose that under such circumstances the polarities of its molecules might fluctuate to a degree which would produce corresponding modifications of its character; and this, with the motion supplied by molecular vibration, would constitute a moving equilibrium almost sufficient to bridge the gap between animate and inanimate existence.

Regarding life as a process of adjustment of inner to outer relations, matter in such a state would possess the mobility of constitution without which life-adjustment would be impossible, and it would also possess the motion without which such an adjustment could not be carried into effect. But it is clear that these are not quite sufficient. Mere capability of chemical modification by its environment will not turn dead into living matter. However elastic such a capability might be, it could not provide for the complex adjustments involved in nutrition and growth. Something more is needed to change this passive capability of modification by, into a capability of active response to, external stimuli, and thereby to give the process of adjustment that purposive and selective character which seems to be of the essence of life. It is obvious what this something must be. It must be some form, however faint, of sentience.

Since, therefore, life can find its necessary mobility in matter, can it not also acquire its necessary sentience from the same source? I think the answer to this question may be found in the late Professor Clifford's doctrine of Mindstuff.' A full account of this is given in an article by him on The Nature of Things-in-Themselves,' in Mind, vol. iii. (1878), p. 57. But his conclusions, so far as they relate to the present subject, may be summarised as follows:

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1. A feeling can exist by itself without forming part of a consciousness.

2. That element of which even the simplest feeling is a complex he calls Mindstuff;' and these elemental feelings which correspond to motions of matter are connected together in their sequence and coexistence by counterparts of the physical laws of matter.

3. A moving molecule of inorganic matter does not possess mind or consciousness, but it possesses a small piece of mindstuff. When molecules are so combined together as to form the film on the underside of a jellyfish, the elements of mindstuff which go along with them are so combined as to form the faint beginnings of sentience.

When the molecules are so combined as to form the brain and nervous system of a vertebrate, the corresponding elements of mindstuff are so combined as to form some kind of consciousness. When matter takes the complex form of a living human brain, the corresponding mindstuff takes the form of a human consciousness, having intelligence and volition.' 13

Such in brief is the theory of mindstuff, and though I do not think it can be accepted unreservedly, it lends great help to the present inquiry. Clifford's premature death prevented any further elucidation of the subject by him, and some of its points are left in unwelcome uncertainty. Prima facie we should suppose that mindstuff was something material, but Clifford seems to evade this conclusion, and to treat mindstuff, first, as something distinct from but inseparably connected with matter, and, later, as the one absolute reality of which matter is only a manifestation. However, I think there can be little doubt that, according to his original idea, mindstuff was something in its nature material. A moving molecule of inorganic matter possesses, he says, 'a small piece of mindstuff." These words can mean nothing unless mindstuff is to be credited with quantity and extension. But that which has quantity and extension we can only regard as matter; and this view I am prepared to adopt. With respect, however, to the association of matter and mindstuff, I do not think that we can regard this combination as consisting of a double atom of matter and mindstuff. I think rather that we must distinguish matter proper and mindstuff as two forms of matter, diffused in their original condition separately through the universe; though this apparent duality of substance will disappear, as will be seen later, under a somewhat different analysis.

But this primitive sentience which comes in as the crowning factor of life is something more also: it is the first germ of soul. There is a tendency in force, pointed out by Dr. Maudsley, to develop upwards, and consequently a tendency in organic substance, even when life has fled, to resist, as he puts it, 'the extreme retrograde metamorphosis of material and force before being used up again in vital compounds.' 14

Let us see how this will apply to the growth of soul. For the convenience of discussion I retain matter' and 'mindstuff' as distinctive terms, but it must be clearly understood that mindstuff is in its nature material.

It is possible, perhaps, that mindstuff can cohere mechanically with simple matter; but I do not think that it could combine physiologically, except with matter of a certain complexity. The

13 In a note to this article Professor Clifford remarks that he had found traces of his theory in other writers, mentioning particularly Kant and Wundt. To these may be added Spinoza, Schopenhauer, and perhaps Herbert Spencer.

14 Body and Mind, p. 282.

earliest forms of life present such a combination, and from such forms soul growth, as well as physical growth, originates. Where living matter has only assimilated mindstuff enough to give it mere sentience, when physical life ceases, the mindstuff may perhaps be released from combination in its original simple condition. But as physical life mounts higher, soul-life follows in its train. Every advance in physical complexity brings with it higher mental needs and higher mental possibilities. The simple mindstuff which suffices to supply unmodified protoplasm with its feeble sentience is replaced in the higher organisms by mindstuff grouped into a mental structure. When such a higher physical organism dies, the mental organism belonging to it does not forth with decompose back into simple mind-stuff, but normally retains its organic unity, and in this state can be appropriated again by a physical organism, but only by an organism at least as highly developed as its last. In the order of purely physical development we find that the lower organisms commonly draw the materials for their growth and nutrition from inorganic nature.15 Thus the plant depends for its nourishment on a proper supply of carbon, oxygen, hydrogen, &c., and these inorganic materials it works up within itself into protoplasm. But higher organisms, such as the vertebrates, depend for their nutrition on a proper supply of formed protoplasm. The ox, for instance, is nourished by the formed protoplasm of the grass which it assimilates, as the man, in turn, may be nourished by the formed protoplasm of beef. Similarly in the order of mental development. As in due course of evolution higher and higher organisms appear, these cease to draw solely upon simple mindstuff for their mental needs (though probably enough they may use it for some lower sentient purposes), but in virtue of their greater complexity require, and are able to appropriate, the formed mindstuff structures fashioned by lower organisms, and gradually to group them into mental structures of a higher complexity. Thus the whole mental fabric of a lower form of life may be merely one of the molecules, as it were, which compose the consciousness of a higher form. This process continues till some mental structure is reached upon which self-consciousness dawns; with self-consciousness arises for the first time the ego' or soul; and at this point we may safely assert that no known organism can group it any further.

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It would be as rash to declare that a mental organism never undergoes the extreme of decomposition as it would be to make a similar assertion of a physical organism. But what is true of the latter is probably true of the former, and we are entitled to think that a mental organism tends to cohere as such, instead of sinking back into simple mindstuff.

But how does self-consciousness spring from mere consciousness? 15 Certain fungi, I believe, can assimilate organic matter.

How can a mere capability of apprehending sensations furnish the idea of an 'ego' that apprehends? In some way or another consciousness becomes able to turn from the perception of sensations as such, to a cognition of the sensations as states of itself. And how is this brought about? The question is not an easy one, but I believe the explanation is to be found in the structure of the mental organism. At first sight it may seem unwarrantable to treat our highest human quality as a mere product of structure, but a little consideration will show how closely quality and structure are connected. We are bound to regard matter in its simplest form as homogeneous; how, then, did it come by its present diversity of qualities? These are clearly the results of various molecular groupings -in short, of structure. A striking proof of what diversities of quality structure can produce is shown by the isomerism' of chemistry. Substances composed of the same elements, and in the same proportions, are chemically described as isomeric. But the properties of isomeric bodies often differ widely, as may be seen in the case of starch, gum, and a certain form of sugar. These are all isomeric, and their differences depend simply on the different arrangement of their component molecules. And be it observed, the more complex the structure, the higher as well as the more numerous will its properties be.

In the case of a mental organism, the very fact that, with all endeavour, we cannot get at the back, so to speak, of our self-consciousness strongly suggests that this self-consciousness is not an independent entity, but a property of structure. If we still press for some mechanical account of how self-consciousness operates, we may arrive at some such conclusion as this. Consciousness is a mental structure which responds more or less perfectly to nerve-stimuli. If this response be translated into terms of matter, we must regard it as being in itself a sort of thrill. Indeed psychologists describe the ultimate unit of consciousness as a 'psychical shock' or 'tremor '—a view which seems to me to imply necessarily the materiality of the consciousness in which the shock or tremor takes place. But these units are not themselves objects of consciousness, they are only the elements of which conscious states are composed; and thus, paradoxical as it sounds, every state of consciousness is built up of unconscious or subconscious elements. Accordingly, in the mind-structure of an animal incapable of self-consciousness, a conscious state is just a responsive thrill. Now to every such thrill there must naturally be a recoil, and in such a mental structure as we are now considering, this recoil would either pass off in some of the commoner forms of force,16 or its units, if affecting the mind-structure at all, would never rise above the subconscious level. But in the more sensitive and complex mind-structure of the man, the recoil might, partly at any

16 Professor Lombard has succeeded in measuring the heat given off by the cerebrum during mental operations.