of the ultimate morphological components of organisms, the powers of the various aggregations of such components, i.e. of the various tissues' and the functions of the different special aggregations and arrangements of tissues which constitute organs.'

But as each living creature is a highly complex unity— both a unity of body and also a unity of force, or a synthesis of activities-it seems to me that we require a distinct kind of physiology to be devoted to the investigation of such syntheses of activities as exist in each kind of living creature. I mean to say that just as we have a physiology devoted to the several activities of the several organs, which activities are the functions of those organs, so we need a physiology specially directed to the physiology of the living body considered as one whole, that is, to the power which is the function, so to speak, of that whole, and of which the whole body, in its totality, is the organ.

In a word, we need a physiology of the individual. This science, however, needs a distinct appellation. I think an adequate one is not far to seek.

Such a line of inquiry may be followed up, whatever view be accepted as to the nature of those forces or activities which living creatures exhibit. But if we recognise, as I myself think our reason calls on us to recognise, the existence in each living being of such a principle of individuation' as I have advocated the recognition of, then an inquiry into the total activity of any living being considered as one whole is tantamount to an inquiry into the nature of its principle of individuation. Such an inquiry becomes 'Psychology' in the widest and in the original signification of that term-it is the Psychology of Aristotle.

Mr. Herbert Spencer has already made a great step towards reverting to this original use of the term, for he has made his 'Psychology' conterminous with the animal king

dom, having made it a history of the psychoses of animals. But the activities of plants must not be ignored. A science which should include the impressionability and reactions of a Rhizopod, and exclude the far more striking impressionability and reactions of Venus's Fly-trap, and of other insectivorous plants, the recognised number of which is greatly on the increase, must be a very partial and incomplete science. If Psychology is to be extended (as I think Mr Spencer is most rational in extending it) to the whole animal kingdom, it must be made to include the vegetable kingdom also. Psychology, thus understood, will be conterminous with the whole of Biology, and will embrace one aspect of organic dynamics, while Physiology will embrace the other.1

PHYSIOLOGY will be devoted (as it is now) to the study of the activities of tissues, of organs and of functions, per se, such, e.g., as the function of nutrition, as exhibited in all organism from the lowest plants to man, the functions of respiration, reproduction, irritability, sensation, locomotion, etc., similarly considered, as manifested in the whole series of organic forms in which such powers may show themselves.

PSYCHOLOGY will be devoted (according to its original conception) to the study of the activities of each living creature considered as one whole-to the form, modes, and conditions of nutrition and reproduction as they may coexist

in

any one plant; to these as they may coexist with sensibility and motility in any kind of animal, and finally to the coexistence of all these with rationality as in man, and to the interactions and conditions of action of all these as existing in him, and here the science which corresponds to the most narrow and restricted sense of the word, psychology, i.e. the subjective psychology of introspection, will find its place.

Psychology, in the widest sense of the term, in its oldest, and in what I believe will be its ultimate meaning, must. 1 As before pointed out, see ante, vol. i. p. 429.

necessarily be, as to its details, a science of the future. For just as Physiology requires as a necessary antecedent condition a knowledge of anatomy-since we must know that organs exist before we investigate what they do-so Psychology requires as a necessary antecedent condition an already advanced physiology. It requires it because we must be acquainted with the various functions before we can study their synthesis and interactions.

When, however, this study has advanced, one most important result of that advance will be a knowledge, more or less complete, of the innate powers of organisms, and therefore of their laws of variation. By the acquisition of such knowledge we shall be placed in a position whence we may advance, with some prospect of success, to investigate the problem of the 'Origin of Species'—the biological problem of our century.

This reflection leads me back once more to my startingpoint, the merits of the great French naturalist of the last century, whose views as to variation, and as to animal psychosis, have enabled me to bring before you the questions on which I have presumed to enter. Buffon's claims on our esteem have, I think, been too much forgotten, and I rejoice in this opportunity of paying my debt of gratitude to him by recalling them to recollection. As to the questions which his words have suggested to me and upon which I have thus most imperfectly touched, the considerations I have ventured to offer may or may not commend themselves to your approval; but, at least, they are the result of not a few years of study and reflection, and I am persuaded they have consequences directly or indirectly affecting the whole field of biological inquiry, which belief has alone induced me to make so large a call upon your patience and your indulgent kindness.

VOL. II.

Р

ONE

FORCE, ENERGY, AND WILL.

NE benefit due to the advance of physical science is, as Professor Clerk Maxwell has remarked, the introduction into common speech of words and phrases consistent with true ideas about nature instead of others implying false ideas. But though our scientific progress has produced this amongst so many other beneficent effects, yet, as its advancing stream has left here and there a stagnant pool, so we may not unreasonably expect every now and then to meet even with a temporary verbal backwater. Thus electrical discovery by the term 'electric fluid' has left in the popular mind the illusion that electricity is a fluid substance which flows from one body to another. But a really grave misconception (in some respects a retrograde error) appears to me to be coming daily more diffused with regard to the conceptions 'energy' and 'force.'

1

The term 'force' has, of course, definite and exact meanings (not always quite consistent, however,) assigned to it in 1 Thus Professor Tait, in his Lectures on Some Recent Advances in Physical Science, defines (at page 16) 'force' as any cause which alters or tends to alter a body's natural state of rest or of uniform motion in a straight line.' At page 354 he says: Force is the rate of change of momentum,' and adds that the term 'is obviously to be applied to any pull, push, pressure, tension, attraction or repulsion, etc., whether applied by a stick or a string, a chain or a girder, or by means of an invisible medium such as that whose existence is made certain by the phenomena of light and radiant heat.' At page 358 he adds: Force is the rate at which an agent does work per unit of length.' In Nature, July 5, 1877, he tells us: In all probability there is no such thing as force.' Force is often taken to denote the unknown cause of energy,' 'energy being the power possessed by a body of overcoming a resistance. Force is also defined as 'mass animated by velocity, or directed pressure.'

own.

physics; but it is the more general, not the exact use of the term to which reference is here made. Force' becomes known to us partly through the sense of effort and resistance overcome which attends our muscular activity, and partly through the exercise of will, as perceived in exerting our voluntary mental activity-force of mind being a term of familiar use as well as force of arm. We have, therefore, force in our own being as the active exercise of mental and bodily powers which are possessed by our complex organisms. The sensations of effort and resistance we experience, are the occasions through and by which our intellect comes to perceive that surrounding bodies have powers corresponding to our We do not, however, as some pretend, attribute to surrounding bodies activities such as our own, but only activities having a certain analogy with ours. If we try to pull a man up from the ground against his will, and fail from his being more muscular than we are, and if we try to pull up a stone from the ground and fail from its being too heavy to lift, we do not attribute muscular activity to the stone, or to the earth which by gravity retains it; but we perceive a certain relation of analogy between the pulling activity of the man and the pulling activity of the earth, and this though our own sensations constitute the one material by means of which our intellect has the power of apprehending those two very different perceptions. As it is with gravity, so with the other influences (luminous, calorific, electrical, etc.) which surrounding bodies bring to bear on us; we naturally recognise them as the actively exercised powers and properties of such bodies. The sleeper who wakes to find that the earth's rotation has carried him from beneath a tree's friendly shade into the direct influence of a scorching sun, believes that the heat he experiences is due to the activity of that great body acting upon his own organisation, and also believes that activity to be something radically and essentially different